UNIVERSITY OF WISCONSIN-LA CROSSE Graduate Studies

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1 UNIVERSITY OF WISCONSIN-LA CROSSE Graduate Studies A SINGLE INSTITUTION S EXPERIENCE IN DEVELOPING A PURPOSEFUL AND EFFICIENT OFF-LINE TECHNIQUE FOR ADAPTIVE RADIOTHERAPY IN A CLINICAL ENVIRONMENT A Research Project Report Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Medical Dosimetry Charles E. Poole, CMD, B.S. College of Science & Health Medical Dosimetry Program November, 2012

2 2 A SINGLE INSTITUTION S EXPERIENCE IN DEVELOPING A PURPOSEFUL AND EFFICIENT OFF-LINE TECHNIQUE FOR ADAPTIVE RADIOTHERAPY IN A CLINICAL ENVIRONMENT By Charles E. Poole, CMD, B.S. We recommend acceptance of this project report in partial fulfillment of the candidate's requirements for the degree of Master of Science in Medical Dosimetry The candidate has met all of the project completion requirements. Nishele Lenards, M.S. Graduate Program Director November 9, 2012 Date

3 3 The Graduate School University of Wisconsin-La Crosse La Crosse, WI Author: Poole, Charles E. Title: A Single Institution s Experience in Developing a Purposeful and Efficient Offline Technique For Adaptive Radiotherapy in a Clinical Environment Graduate Degree/ Major: MS Medical Dosimetry Research Advisor: Nishele Lenards, M.S. Month/Year: November, 2012 Number of Pages: 55 Style Manual Used: AMA, 10th edition Abstract Adaptive Radiotherapy (ART) strategies evolved from advances in Image-Guided Radiation Therapy (IGRT) technologies. The purpose of this study is to develop a purposeful and efficient technique to adapt a patient s radiation therapy (RT) plan utilizing a computed tomography on rails (CTOR) image guidance system and to describe the experiences incorporating this technique into a single institution s clinical environment. Adapting a patients course of RT may be necessary because of tumor growth or regression, biological changes in anatomy or tumor volume and positional or localization changes observed in patients. This study was a retrospective review of 9 patients treated for lung carcinoma comparing CTOR data sets to the initial planning computed tomography (CT) data sets from the 10th, 20th, and 30th fractions of RT. Tumor volumes, dose changes, and coverage from CTOR data sets compared against initial CT data sets were analyzed and a percent deviation was used to report these changes. Adapting the initial RT plan to reflect these changes provided a precise RT plan and avoided potential overdosing or under dosing of target volumes. Adaptive radiotherapy continues to benefit the patient and improves their overall survival as the field of radiation oncology continues to adapt to rapidly changing technology.

4 4 The Graduate School University of Wisconsin - La Crosse La Crosse, WI Acknowledgments I would like to thank Sicong Li, D.Sc., at the University of Nebraska Medical Center, Omaha, Nebraska for his contributions in assisting on this study and helping me to further my education in medical dosimetry.

5 5 Table of Contents...Page Abstract...3 List of Tables...6 List of Figures...7 Chapter I: Introduction...8 Statement of the Problem...10 Purpose of the Study...11 Assumptions of the Study...11 Definition of Terms...11 Limitations of the Study 15 Methodology...16 Chapter II: Literature Review...17 Chapter III: Methodology...32 Sample Selection and Description...32 Instrumentation...33 Data Collection Procedures...34 Data Analysis...36 Limitations...36 Summary...36 Chapter IV: Results...38 Item Analysis Chapter V: Discussion...43 Limitations...43 Conclusions...43 Recommendations...45 References...52

6 6 List of Tables Table 1: Patient Tumor Volumes from TPS and the Percent Change...47

7 7 List of Figures Figure 1: Total Tumor Volume Change Over the Course of RT...48 Figure 2: Tumor Volume Changes by Fractionation Intervals..48 Figure 3: Normal Tissue Percent Change for Patient 1.49 Figure 4: Normal Tissue Percent Change for Patient 4.49 Figure 5: Normal Tissue Percent Change for Patient 5.50 Figure 6: Normal Tissue Percent Change for Patient 7.50 Figure 7: Normal Tissue Percent Change for Patient 9.51 Figure 8: Normal Tissue Percent Change per Patient...51

8 8 Chapter I: Introduction Adaptive radiotherapy is an emerging technique that has been incorporated into many clinical radiotherapy applications. Due to the advances in RT planning and treatment delivery techniques, the field of radiation oncology has advanced as new multimodality imaging techniques have been developed and incorporated into RT treatment delivery. 1 Innovations in CT, magnetic resonance imaging (MRI), and positron emission tomography (PET) have made tumor volumes easier to delineate and nearby critical structures identifiable. 1 The goal of RT is to irradiate the tumor volume while minimizing radiation to the surrounding critical structures. With better tumor volume and critical structure delineation, RT techniques enable dose to be escalated to tumor volumes. 2 The advancements of three-dimensional conformal radiation therapy (3DCRT), intensity modulated radiation therapy (IMRT), and stereotactic body radiotherapy (SBRT) have paved the way for more precise tumor delineation and localization methods. 3 These highly conformal RT techniques deliver high doses of radiation to the tumor volume and enable rapid dose falloff near critical structures. 4 High radiation doses and rapid dose falloff have been the driving force behind developing more accurate imaging for tumor delineation and localization. 4 Eliminating the uncertainties in positioning due to intra- and interfractional motion, respiratory motion, and daily tumor volume changes are needed to prevent a geometric miss and thereby underdosing the tumor volume. 2 Image-guided radiation therapy technologies enable accurate imaging for tumor delineation and localization, reduce the uncertainties in tumor and respiratory motions, reduce daily patient setup errors, and allow for accurate dose escalation to the tumor volume. 1 Imageguided radiation therapy technologies combine the developments and innovations made in multimodality imaging with RT treatment planning and delivery. 1 Several IGRT technologies that have had a significant impact over the last decade include electronic portal imaging devices (EPID), megavoltage (MV) and kilovoltage (KV) cone beam CT (CBCT), and in-treatment room CT scanners. 1 The impact of these technologies facilitates more precise RT planning and delivery to patients by allowing for daily or weekly adaptations of the treatment plan. The various IGRT technologies can be classified into a two-dimensional (2D) planar approach such as EPID or a 3D volumetric approach like KVCBCT. 1 Volumetric 3D IGRT approaches can facilitate online or off-line corrections to treatment plans to account for any adaptations due to motion or reductions of the tumor volume. 5 If IGRT images are evaluated before a RT treatment and these images are compared and corrected against a reference image set, the adaptation is

9 9 considered to be online. 4 The off-line approach to ART is acquiring multiple IGRT image sets during a small number of RT treatments without immediately evaluating the image set against a reference image set, but instead adapting the RT plan after a number of RT treatments. 4 Imageguided radiation therapy techniques allow for daily adaptations of the RT target volumes within a fraction or between fractionations to account for patient positioning or motion and anatomical or tumor volume changes by image registration. 4 Image registration and fusion of the RT planning images and the daily or weekly IGRT images are integral components for ART. Image registration and fusion can be used frequently in treatment planning for tumor localization, treatment delivery, and assessing tumor responses. 6 The registering of multiple sets of images requires finding common geometric coordinates, lines and surfaces, or using an intensity-based grayscale system between the image sets to measure how they registered. 6 The idea behind multiple image registration is to be able to map information from one set of images to another (set of images) by fusing the image sets together. 7 Fusing multiple image sets together helps to delineate tumor volume changes, critical structures, and tumor volume localization. By using the process of image registration and fusion, ART can improve RT to limit tumor volume margins, escalate tumor doses, and reduce patient toxicities during treatment. The ART technique is a process that incorporates IGRT and image registration and fusion to adapt a patient s initial radiation treatment plan by assessing tumor volume changes, tumor motion, and critical structure changes in response to radiation. This adaptation can be either an online approach or off-line approach that utilizes various IGRT technologies. The rationale for ART is to adapt the RT plan to the changes that are observed anatomically either by an online or off-line strategy. While each strategy provides the ability to verify setup accuracy, assess organ and tumor volume changes daily, the two strategies provide different time frames to adapt a RT treatment plan. The online strategy utilizes daily IGRT technologies to perform immediate adaptations to the RT treatment plan, on the same day before the treatment fraction is delivered as a result of anatomical changes. Online ART can provide immediate adjustments to the RT plan by verifying setup accuracy, organ motion, and tumor volume changes. 1 The off-line strategy utilizes IGRT technologies to perform adaptations to the RT treatment plan for future RT treatment fractions, not on the same day as with the online strategy. The online ART strategies can be interpreted as making intra-fractionation changes to a treatment plan, whereas,

10 10 off-line ART strategies imply making inter-fractionation changes to the plan at certain intervals that may occur over the whole course of the treatment. One of the most prevalent disease sites the strategies of ART has made a difference is in the treatment of lung cancer. The most important factor in treating lung cancer is the management of moving tumor volumes and respiratory motion. Geometric uncertainties have a big impact on the accuracy of treatment planning, imaging, and treatment delivery in lung cancers. 8 The uncertainties stem from respiratory motion, both inter-fractional or intra-fractional setup errors, and microscopic disease growth that is unseen. 8 To account for these geometric uncertainties larger margins are constructed and irradiated in lung patients. 8 Typically, generous safety margins are incorporated around the target to allow for tumor coverage and ensuring geometric uncertainties are accounted for. 8 The role ART plays in the treatment of lung cancer has evolved with the advancements of IGRT, IMRT, and four-dimensional (4D) image based motion management. 2 With 4D motion management, respiratory motion of the tumor volume is delineated on multiple CT scans to acquire a motion encompassing internal target volume (ITV) from the patients breathing cycle. 8 The concept of generating an ITV is to capture the gross tumor volume (GTV), clinical target volume (CTV), and internal motion (IM) of the tumor volume in all phases of the respiratory cycle. The IM takes into account any physiological movements and variations in size, shape, and position of the tumor volume. 9 An additional volume called a planning target volume (PTV) is expanded from the ITV and this PTV is a representation of all phases of the patients breathing cycle and it is often used in treatment planning as the volume to be irradiated. This volume ensures that when the radiation beam is turned on, the radiation will hit the tumor volume no matter what phase the patients breathing cycle is in. Adaptive radiotherapy strategies play significant roles in the treatment of lung cancer and the focus of this paper is to develop a method to incorporate an ART strategy at one institution. Statement of the Problem The increasing challenge in RT is keeping up with the dynamic technologies. One of these challenges is creating an efficient method of ART using IGRT technologies. Several studies have been done incorporating IGRT technologies with ART in patients with bladder cancer. 10,11,12 Image-guided radiation therapy technologies are being utilized prior to a patients daily RT treatment for localization and positioning. The CTOR technology enables tumor localization and patient positioning daily or even weekly prior to a patients radiation treatment.

11 11 The soft tissue delineation and the accurate tumor localization components are benefits of the CTOR technology. However, very few studies have been done incorporating the CTOR technology for the adaptation of lung tumors. Developing an ART strategy utilizing CTOR technology periodically to monitor tumor volume changes in order to adapt the treatment plan potentially benefits the patients long term outcome. This is a single institution s experience in developing a purposeful and efficient off-line technique to incorporate ART in a clinical environment for the treatment of lung cancer. Purpose of the Study The goal of this study is to develop a purposeful and efficient technique to incorporate ART in a clinical setting for the treatment of lung cancer. This study reviews retrospective data on patients with lung cancer who have undergone definitive radiation treatments utilizing IGRT at the University of Nebraska Medical Center (UNMC). The goal of this study is not only to implement a simple off-line ART technique that is practical and efficient to use for adaptation of RT plans, but also to produce a more conformal treatment plan through adaptation during the patient s course of treatment. Assumptions of the Study No assumptions have been made about this study in terms of tumor volume response or the dose threshold at which a tumor response indicates an adaptation to the treatment plan. All patients had CTOR image guidance in conjunction with their RT treatments. The adaptive replanning of the patient s treatment plan was done with the CTOR data set on every 10th fraction throughout the patient s course of RT. The initial RT treatment plan was consistent throughout all of the adaptive re-plans over the course of the patients treatment. The results of this ART strategy were analyzed using measured tumor volumetric data. Definitions of Terms Active Breathing Coordinator (ABC) A respiratory device which monitors and controls a patient s respiratory cycle during RT for tumors that demonstrate IM. Tumors that are located in the chest and breast move with the patient s respiratory cycle. An ABC device can minimize the IM and immobilize these tumors which allows for greater accuracy of the RT delivery. Adaptive Radiotherapy (ART) The adaptation of a RT treatment plan in response to the changes in the tumor volume, shape, and position observed by daily or weekly IGRT

12 fields. 1 Four-Dimensional Computed Tomography (4DCT) Computed tomography scans 12 techniques. 13 A technique utilized when a patient s RT is re-optimized during the course of the treatment. 10 Clinical Target Volume (CTV) The demonstrated tumor and any other microscopic tissue with presumed tumor. 9 The volume which includes the gross visible tumor and an additional margin for possible microscopic disease extension that may not be visible or palpable. 14 This volume is a non-standard and unique expansion of the GTV and represents the true extent and volume of the tumor. 9 In RT treatment planning, the CTV must receive adequate radiation prescription dose in order to destroy the tumor. 9 Computed Tomography (CT) An ionizing radiation technique that uses an x-ray source and computer technologies to produce a radiographic image. 14 The x-ray source moves in an arc around a body part and as the x-ray beams pass through the body part, the radiation is converted into signals that are projected onto a computer screen, which appear as a radiograph. 14 Computed Tomography on Rails (CTOR) - A form of IGRT in which a diagnostic CT scanner moves on a rail system in the treatment room. The CT scanner is opposite of the treatment machine and has a common couch arrangement. 15 Cone-Beam Computed Tomography (CBCT) Volumetric imaging comprised of planar projection images acquired from a CT scan with flat panel detectors rotating around the patient. 1 The single image projections are acquired with each rotation of the gantry which is slightly offset from the prior rotation to generate a 3D reconstruction data set. 14 Conformity Index (CI) A measurement related to the conformity of dose surrounding the target. The volume of the target enclosed by the 95% isodose line measured in cubic centimeters compared to the total volume of the target. The smaller the CI, the higher the conformity. Electronic Portal Imaging Device (EPID) A linear accelerator-mounted electronic diagnostic imaging device that assists in patient setup, positioning, and verification of treatment acquired at the same time as a respiratory signal that are reconstructed into 3D data sets which represent a patients anatomy during different phases of a respiratory cycle. These 3D CT data sets are known as 4DCT images. 9

13 13 Free-Breathing Motion The displacement or motion of a tumor located in the lung during a patient s normal respiratory cycle. A patient s normal breathing motion has an effect on lung tumor coverage and setup error and must be considered when deriving treatment margins. Gross Tumor Volume (GTV) The gross demonstrable, palpable, or visible extent and location of the malignant tumor. 14 It is the volume of known disease which includes the primary tumor and any involved lymph nodes. 2 Image Fusion The process of combining the enhanced capabilities of different imaging modalities with a CT data set. Fusing different image modalities with a CT data set enables anatomy to be defined on those image sets and displayed on the CT data set. 14 Image-Guided Radiation Therapy (IGRT) - An imaging technique that uses computer created images of the tumor acquired prior to the delivery of RT to help direct the radiation beam to the focal point of the tumor. The various techniques utilized for IGRT make RT more accurate. 16 Image Registration The process of geometrically registering multiple diagnostic imaging data sets to a common coordinate system in order to utilize the information from these multiple data sets. 7 Once the different data sets are registered, information can be integrated between them and combined to assist in RT treatment planning. 7 Image registration of multiple data sets helps to identify corresponding points or regions between the multiple imaging studies. 7 Intensity Modulated Radiation Therapy (IMRT) A RT technique that uses nonuniform fluences (beam intensity profiles) to vary the intensity of the beams across the treatment fields to achieve an optimized composite dose distribution to the tumor volume. 9 This RT technique utilizes multiple beams from different beam directions to maximize dose to the tumor volume while minimizing dose to the surrounding tissues and OR. 9 Internal Motion (IM) A margin added to the CTV to include variations in the size, shape, and position of a tumor volume in relation to the internal physiological movements and respiratory motion of the patient. 9 Internal Target Volume (ITV) In treatment planning, the ITV is a volume which consists of the CTV and the IM to account for any respiratory motion or changes in the size, shape, and position of the target during a RT treatment. 2 This volume is used in conjunction with a setup margin for patient setup uncertainty to define a PTV. 9 Kilovoltage Cone Beam Computed Tomography (KVCBCT) An imaging system that utilizes kilovoltage (KV) x-rays generated by an x-ray tube mounted on a retractable arm

14 14 90 to the treatment beam line of a linear accelerator. 9 A flat panel x-ray detector is opposite of the x-ray tube and multiple KV radiographs are acquired as the gantry rotates around the patient. 9 Magnetic Resonance Imaging (MRI) - Computerized images of soft tissues in the body through the use of magnetic resonance of atoms in the body and applied radio waves. It is a noninvasive diagnostic technique. 16 Mean Lung Dose (MLD) Average radiation dose to the total lung volume minus the GTV. 14 In previous studies which have analyzed RT treatment planning to the lung, the MLD has been established as a predictor of risk in radiation pneumonitis of the lung. 14 A patient may experience an increased risk of radiation pneumonitis if the MLD in the treatment plan is between 15Gy to 20Gy. Megavoltage Cone Beam Computed Tomography (MVCBCT) An imaging system that uses the MV energy of the linear accelerator and an EPID mounted on a retractable support. 9 This system uses a flat panel adapted for MV photons and images are acquired by a continuous arc rotation of the gantry of 180 or more. 9 Image reconstruction is completed following the acquisition. 9 Normal Tissue A term that is used to define all tissues encompassed within the body including all organs located within the body. However, normal tissue does not include the portion of the body tissues that are identified as tumor volumes (GTV or CTV). Normal tissue is all the body tissue abutting the tumor volumes. Organs at Risk (OR) - Critical organs inside the body, near or within the radiation fields that have specific radiation dose tolerances. The radiation dose is limited to these organs. Planning Target Volume (PTV) A geometric volume which includes the CTV and all geometric uncertainties. 14 The margin around the CTV to account for patient motion and setup uncertainties. 9 Positron Emission Tomography (PET) - Radioactive glucose is injected into the body and a nuclear medicine scanner is used to make detailed computerized images inside the body where the glucose is used. Cancer cells often use more glucose than normal cells. 16 Respiratory-Correlated Cone Beam Computed Tomography (rccbct) Similar to 4DCT and used to visualize breathing motion and to correct for motion artifacts. 17 The CBCT images are reconstructed at certain fractions during RT treatment which represent the full respiratory cycle. 17 These data sets may be used to access volumetric tumor changes or positional changes. 17

15 tissues. 9 Treatment Planning System (TPS) Computer systems that are utilized for the 15 Stereotactic Body Radiotherapy (SBRT) - A form of RT that delivers high doses of radiation to tumor volumes in few fractions. This type of treatment concentrates a high degree of dose conformality in the target volume and spares normal tissue. 9 The SBRT technique delivers RT with great accuracy with rapid dose falloff sparing surrounding normal tissues. 14 Therapeutic Ratio The ratio of radiation dose that produces damage in tumor cells to the radiation dose that produces damage in normal cells. The dose response difference of tumor cells to normal cells determines the effectiveness of RT. Three-dimensional conformal radiation therapy (3DCRT) Radiation therapy that is based on 3D anatomic information that conforms to the tumor volume and limits dose to normal planning of RT treatment plans. Treatment planning systems have software that allow for 3D data input and processing, dose calculations, and 3D graphics. 9 The TPS allows for the design, calculation, and evaluation of RT plans for patients who undergo treatment. Tumor Control Probability (TCP) A biologic index that can be used in evaluating a treatment plan which assumes that a tumor is destroyed if all tumor cells are killed. 9 The TCP model assumes that tumor cells in a tumor are evenly distributed and have identical radiosensitivities. 9 If the radiation dose to each tumor cell produces a response independently in a partial tumor volume, then the TCP can be inferred for the whole tumor volume. 9 Limitations of the Study The limitations of this study included the possibility of positional and rotational inaccuracies in the image registration based on inter-observer variations. These variations may affect the tumor volume propagation of the original tumor volumes onto the CTOR data sets. Inaccurate image registrations of multiple data sets may introduce errors into the contours that are propagated onto the CTOR data sets from the original CT treatment planning data sets. Another limitation of this study included the inter-observer variations of tumor volumes and tumor volume responses to radiation. The segmentation of tumor volumes and the determination of whether or not a tumor volume responded to RT was completed and reviewed by 2 radiation oncologists (RO) and was subject to interpretation. Additional limitations included tumor volume responses from neo-adjuvant or concurrent chemotherapy agents introduced prior to or during RT treatments, truncated CTOR scans which limited the anatomy that could be analyzed for this study, and also the influence of the patients respiratory motion and its effects on the delineation

16 16 of the tumor volumes. A final limitation included the accuracy in which the marker BBs were placed on the patient s treatment isocenter prior to CTOR scans. The marker BBs corresponded to the patient s treatment isocenter and inaccurate placement of these BBs on the CTOR scan may have introduced inaccuracy in transferring the radiation beams onto the CTOR data sets. Methodology This study included a retrospective review of lung cancer patients treated with definitive RT at the UNMC. Retrospective patient data sets including CTOR images and the initial radiation planning CT data sets were used to develop a purposeful and efficient off-line ART strategy that could be incorporated into treatments for lung cancer. This study examined the biweekly CTOR data sets tumor volumes in comparison to the initial planning CT data set to discern if tumor volume reduction had taken place. Tumor volumes were measured and comparatively evaluated. The rationale was to compare volumetric target changes with the anticipation that tumor volumes and treatment margins could be decreased in order to limit toxicity to surrounding normal tissues. Finally, an analysis of the experience and feasibility of utilizing CTOR in conjunction with ART for lung cancer patients at the UNMC was performed and the results were discussed.

17 17 Chapter II: Literature Review The advanced RT imaging and emerging technologies in IGRT have enabled techniques for ART strategies for lung cancer treatments. Advanced image guided systems like CTOR have the ability to visualize the tumor and OR in 3D. 5 This 3D volumetric IGRT system may be used to incorporate ART strategies into the treatment of lung carcinoma. A CTOR system enables the introduction of ART by optimizing treatment fields from inter-fractional changes in position and shape of the target. 18 This IGRT system is comprised of a CT scanner and a linear accelerator positioned at opposite ends of each other in a treatment vault and they both share the same patient couch. 10 When the couch is rotated 180 from the linear accelerator to the CT scanner, the linac isocenter on the couch matches the origin of the coordinate system on the CT scanner. 19 These coordinates are aligned through image registration between the treatment planning CT data set and the daily CT data set. The data sets are registered daily by the radiation therapist to localize the isocenter as well as the treatment target volume. By sharing the same patient couch, the x-axis, y-axis, and z-axis are identical between machines and these coordinates can be used to position the patient isocenter and target region accurately for RT treatments. This visualization not only facilitates tumor delineation and localization, but also assists in the observation of biological changes occurring in tumor volumes and OR during the course of RT, and provides information to adapt a patient s treatment plan daily or periodically. Adaptations can be intrafractional which are considered online approaches or inter-fractional which are considered offline approaches. An online approach makes adjustments to patient position or treatment parameters using data obtained during the current treatment session. 1 Whereas, an off-line approach makes adjustments from an accumulation of information obtained from previous treatment sessions. 1 These 2 ART approaches can be used independently or in conjunction with each other and can provide many benefits to patients with lung cancer. The benefit of using IGRT combined with strategies of ART for lung cancer patients is an effective approach to reducing tumor volumes and treatment fields to limit dose to OR. These online and off-line ART strategies utilizing IGRT technologies not only allow for decreased tumor volumes and doses to OR, but also minimize the patient s exposure to long term toxicities. Adaptive Radiotherapy Strategies Adaptive radiotherapy strategies facilitate many components. Some of these components include precise RT planning and treatment delivery to patients, thereby reducing OR exposures, the ability to reduce OR exposures, which enables dose escalation, and improve local control and

18 18 overall survival. 8 Adaptive radiotherapy strategies can be categorized into off-line techniques or online techniques that both utilize IGRT and image registration as the basis for adaptations to a RT treatment plan. In addition, ART strategies can be paired with respiratory motion techniques to continue to accurately delineate target volumes as it pertains to motion in lung tumors. The inability to track the changes in volume and location in lung tumors can potentially cause a geometric miss. Geometric misses in lung tumors can be attributed to the lack of increased local tumor control irrespective of tumor doses and lung function. Foroudi et al 10 evaluated 2 ART strategies compared to a conventional treatment protocol for invasive bladder cancer. The study examined benefits of an off-line ART strategy for bladder cancer using CBCT to determine treatment accuracy and also examined the possible benefits of an online adaptive process for treating bladder cancer. The off-line ART strategy of this study utilized the first 5 daily CBCT scans, as well as, a CBCT scan on a weekly basis on 5 patients with invasive bladder cancer. The first 5 daily CBCT scans were transferred to the TPS, registered according to the isocenter, and the volumes were all contoured by the same RO. An adaptive CTV was created from an average of the 5 CBCT CTVs from the first week. This adaptive CTV was used to create a single adaptive plan for treatment starting on fraction number 8 and extended throughout the course of RT. Conversely, the study proposed a theoretical online ART strategy to investigate using the planning CT and the first 5 daily CBCT scans to create small, medium, and large bladder volumes which correlated to small, medium, and large adaptive bladder treatment plans of the day. The small plan was determined by the smallest CTVs of all the scans and the large plan was defined by the summation of the largest CTVs from the scans. A medium plan was determined from a volume created half way between the smallest CTVs and the largest CTVs on the axial slices from all the scans. The basis for this strategy was to use daily IGRT imaging to determine the size of the bladder and select a similar plan based on bladder size prior to treatment. This approach aims to improve target volume coverage while minimizing dose to normal healthy tissue using daily imaging. The coverage was calculated based on the percentage of the CTV that was covered by 95% of the prescription dose. The results of this study comparing the off-line ART strategy to the conventional treatment was an improvement of CTV coverage from 60.1% for conventional radiotherapy to 94.7% for off-line ART. The off-line strategy also demonstrated a higher CI compared to the conventional treatment regimen. In reference to normal tissue irradiation, the study demonstrated a reduction in both ART strategies. More normal tissue was irradiated outside of the CTV using the

19 19 conventional treatment regimen than the adaptive plans and the rectal D50 was considerably lower for each adaptive plan compared to conventional treatment planning. 10 The proposed theoretical online ART strategy which utilized small, medium, and large adaptive bladder volumes, needed further research. The percentage of the CTV that was covered by 95% of the prescription dose for the small, medium, and large adaptive plans was 34.9%, 67.4%, and 90.7% respectively. Online adaptive techniques need more research to reduce systematic errors, random day to day variations, and more education for personnel to delineate soft tissue organs on IGRT images. 10 Another study by Foroudi et al 11 further investigated the advantages and disadvantages of daily online adaptive IGRT compared to conventional RT in 27 patients with invasive bladder cancer. In this study, the online ART strategy as previously described was examined further and a comparison of CTV dose coverage, as well as, the volume of normal tissue irradiated between an online adaptive treatment technique and a conventional technique was done. The adaptive online approach incorporated small, medium, and large bladder volumes with 0.5 cm PTV expansions from the CTVs. Each volume was contoured from the planning CT and the first 5 daily CBCT scans. To determine inter-observer variability in the CTV, the first 7 CBCT scans were contoured and determined that the variability in CTV was less than 5%. For daily treatment beginning on the eighth fraction, the patient was positioned at the isocenter and a CBCT scan was performed. By imaging the bladder volume each day with IGRT, a plan based on the size of the bladder (small, medium, or large) could be chosen for treatment. The results of this study indicated the online ART approach was feasible and the V95 CTV coverage for the ART technique was similar to the conventional technique. The results indicated that for the adaptive treatment component, the small, medium, large, and conventional plans were used in 9.8%, 49.2%, 39.5%, and 1.5% of the cases respectively. 11 The adaptive strategy resulted in 2.7% of the cases having a CTV V95 <99% compared to 4.8% conventionally. In addition, the use of an adaptive technique significantly reduced the volume of normal tissue being irradiated. 11 The normal tissue mean volume receiving a radiation dose of 45Gy or more was 29% less with the adaptive approach compared to the conventional approach. 11 The researchers in this study concluded that the V95 coverage with the ART strategy was comparable to the conventional RT. However, ART strategy significantly reduced the volume of normal tissue being irradiated. 11 Vestergaard et al 12 compared 3 different ART strategies for 10 patients with bladder cancer. The RT treatments incorporated CBCT imaging and plan selection from a library

20 20 consisting of 3 IMRT plans corresponding to small, medium, and large tumor volumes. This study compared integral dose and the normal tissue sparing of different ART strategies. Each of these methods was compared to a standard non-adaptive plan. Each of the 3 ART methods derived different treatment margins that corresponded to small, medium, and large tumor volumes. Adaptive radiotherapy method A utilized population-based treatment margins calculated from a previous study that used an algorithm to determine treatment margins based on CTV coverage in six orthogonal directions. Using this data, the researchers obtained margins needed in all six directions to cover 50%, 70%, and 90% of the population. 12 This corresponded to small, medium, and large plan selection for this method. 12 Adaptive radiotherapy method B utilized the first 5 CBCT scans and did not delineate a target. In method B, the adaptive plan selection was determined by manually comparing the bladder size to a CTV that was delineated by a RO one week prior to RT treatment. A small plan selection was defined as the CTV plus a 0.5 cm expansion. A medium plan selection was defined from overlaying the CTV on the first 5 CBCT scans and adjusting the CTV to each of the 5 CBCT scans. A large plan selection was defined as the CTV plus a 2 cm expansion. The small, medium, or large plans were selected by overlaying the previously contoured CTV with expansions on the first 5 CBCT scans in the TPS to determine which plan matched closest. The ART method C utilized the CBCT scans from the first 4 treatments to delineate a target CTV on the treatment planning CT and determine which plan to select. In each these methods, 3 corresponding PTVs were derived with a 3 mm expansion to account for intra-fractional changes of the bladder. The results of this study determined that differences of these 3 ART methodologies were small compared to each other. However, the ART methodology differences compared to a non-adaptive plan methodology was significant. Treatment volumes reduced from 30% - 40% with ART methodologies and all 3 ART methods had considerable reductions in volumes of normal tissue being irradiated. These large reductions may enable significant dose escalation and keep morbidity levels tolerable. 12 Benefits of Adaptive Radiotherapy Fox et al 20 conducted a study of 22 patients that incorporated multiple CT scans during the course of RT to assess the possibility of reducing treatment volumes in patients with nonsmall cell lung cancer (NSCLC). An initial planning CT scan and 2 additional diagnostic CT scans were performed at 30Gy and 50Gy to assess GTV changes. Respiratory-correlated 4DCT scans were used to evaluate the respiratory effects in 17 of 22 patients. The GTV was delineated on the CT treatment planning scan, as well as the repeated respiratory-correlated 4DCT scans.

21 21 The 4DCT images were registered with the treatment planning CT on the TPS for evaluation of GTV changes. The findings reported a mean GTV reduction of 25% when the patient reached a dosage of 30Gy and a mean reduction of 43% at 50Gy. They found no significant difference in tumor reduction from the location of the GTV in the mediastinum or in the lung parenchyma. Also, the use of chemotherapy did not impact the tumor volume reductions. The reported data suggested greater tumor volume changes occurred at the front part of a course of RT treatment and these changes could not be used as a prediction model for the remainder of the RT course. From this data, they inferred that an adaptive planning strategy could be utilized to escalate dose to the tumor volumes and minimize dose to normal tissues. 20 Siker et al 21 performed a study that assessed the tumor volume changes in 32 NSCLC patients using megavoltage CT scans. An initial planning CT was performed and multiple megavoltage CT scans were done weekly. Seven patients were excluded in this study due to extensive atelectasis which presented a challenge defining tumor borders on the megavoltage CT scans. The remaining 25 patients had a different number of megavoltage CT scans; however, all patients had at least an initial megavoltage CT scan at the beginning, middle, and end of the RT course. A GTV was contoured on each megavoltage CT scan and was assessed for volume reduction. They reported by the end of treatment none of the patients had a complete response, however 3 patients (12%) had a partial response, 5 patients (20%) had a marginal response, and the remaining 17 patients (68%) had stable disease in terms of tumor volume changes. Ten patients (40%) demonstrated greater than 25% tumor regression and none of the patients treated palliatively demonstrated any tumor regression. They concluded that the clinical significance of this tumor volume regression was questionable. The researchers concluded that megavoltage CT offers a viable way to measure gross tumor volume regression and enables accurate assessment of lung tumor volume changes. 21 However, clinically significant tumor regression is still questionable because there is no way to document subclinical disease response which would have a direct impact on treatment field reductions during radiotherapy. 21 Guckenberger et al 22 conducted a study of 13 patients to evaluate the potential of ART for advanced stage NSCLC. The aim of this study was to analyze tumor regression as radiation dose is accumulated and to quantify the potential of ART. An initial 3DCRT treatment plan was generated for each patient, which incorporated an initial 4DCT scan to assist in the contouring of the tumor volumes and OR. The study incorporated weekly diagnostic CT images to analyze tumor regression and used the CT images from the second and fourth weeks of treatment to

22 22 simulate ART for weeks 3 and 5. The treatment plans were adapted to the GTV shrinkage once in week 3 or once in week 5 (single plan adaptations) and twice in weeks 3 and 5 (double plan adaptations) throughout the course of RT. 22 This study reported a continuous tumor regression by 1.2% per day which resulted in a remaining GTV of 49% after 6 weeks of treatment. The data for a single plan adaptation in week 3 and in week 5 reported a MLD reduction of 5.0% and 5.6% respectively. A double plan adaptation performed with CT data and weekly CT images in weeks 3 and 5 combined resulted in a MLD reduction of 7.9%. Plan adaptation to tumor volume shrinkage once or twice during the RT course significantly reduced the MLD which enabled dose escalation to the tumor volumes. 22 Another study by Guckenberger et al 13 which incorporated data from a previous study by Guckenberger et al, 22 evaluated whether or not dose coverage compromised microscopic disease from adapting the radiotherapy treatment plans in response to a shrinking GTV in 13 patients with NSCLC. The concern was that areas of microscopic disease might become under dosed if radiation fields are adapted to GTV reduction and the microscopic disease exhibits no response and remains stationary in the lung tissue. 13 In this retrospective study of 13 patients, the influence of ART planning on dose distributions was simulated for 2 scenarios concerning microscopic disease. 13 Tumor control probability calculations were utilized to evaluate the clinical potential of ART considering doses to the GTVs and microscopic disease. 13 One scenario was the reduction of microscopic disease at the same rate as the GTV reduction, and the second scenario was that the microscopic disease exhibited no response while the GTV reduced. In the first scenario of the microscopic disease reducing at the same rate as the GTV, ART did not influence radiation doses to the GTV or the GTV-PTV region compared with planning without ART. 22 In the second scenario where the microscopic disease exhibited no response while the GTV demonstrated reductions, the volume of microscopic disease that received 50Gy was greater than 95% in 12 of 13 patients for the GTV and greater than 90% in 10 of 13 patients for the GTV-PTV region. These results demonstrate that when adapting a RT treatment plan based on GTV reductions, the dose coverage of the microscopic disease receiving 50Gy is not compromised in either scenario by ART. Adapting the radiation field sizes once or twice in response to GTV reductions during a course of radiotherapy for NSCLC does not compromise dose coverage or TCP of microscopic disease. 13 Adaptive radiotherapy has the potential to increase TCP by greater than 40% compared to radiotherapy planning without ART. 13

23 23 Kupelian et al 23 reported on the rate of tumor regression of NSCLC in 10 patients treated with helical tomotherapy using the Hi-Art system (TomoTherapy Inc. Madison, WI) by evaluating serial megavoltage CT images. The patients in this study had multiple megavoltage CT scans performed over the course of treatment; however, all patients had a scan at the start of RT and at the end of treatment. A GTV was delineated on each megavoltage CT scan to assist in calculating and evaluating tumor regression. The tumor volume response to treatment was demonstrated by the megavoltage CT images from the TPS and quantified over time. 23 The megavoltage CT images evaluated the effects of anatomic variations on the dosimetry of the delivered radiation. 23 To determine the radiation dose distribution, the treatment plan parameters were used and the planned fluence patterns were recalculated on the megavoltage CT images. 23 By utilizing the megavoltage CT images, the radiation dose distribution was adapted to reflect the shrinking tumor volumes. 23 The results of this study documented tumor regression in all 10 patients and the decrease in volume was seen throughout the entire course of RT, not just at the beginning of treatment or the end of treatment. It was reported that individual tumor regression rates ranged from 0.6% to 2.3% per day and the average decrease in volume for all 10 patients was 1.2% per day. 23 Similar to the study conducted by Kupelian et al, 23 Woodford et al 24 also used daily imaging from a megavoltage CT on a helical tomotherapy machine prior to each patient s RT treatment to report the GTV changes and GTV variations in 17 patients treated for NSCLC. To evaluate changes and variations of the GTV, the contours were retrospectively delineated on the daily megavoltage CT scan for each patient. The decrease in size of the GTV reported over 30 fractions of treatment ranged from 12% to 87% and averaged 38% overall. The results determined that no significant correlation was observed between the rate of GTV change and a specified treatment time. 24 In addition, no correlation was observed between the rate of overall GTV decrease and the histological characteristics and staging of the tumor. 24 This study also investigated the potential benefits of ART re-planning with different GTV regression characteristics. By evaluating the 17 patients, 3 general patterns of tumor volume changes were observed. In the 17 patients sampled, 5 patients experienced a small tumor volume change followed by a sharp decrease in tumor volume, 8 patients experienced a gradual tumor volume decrease, and 4 patients experienced variable volume changes with no clear trend in volume reduction. 24 The time frame of when tumor volumes change during the course of radiotherapy can be a strong indicator of whether or not to adapt the treatment plan. Plans adapted near the

24 24 end of RT treatment will be affected very little because the improved plan will be treated over fewer fractions when compared to treatment plans that are adapted earlier. 24 The rate and extent of GTV reduction is variable and patient specific which determines the timing and potential impact of plan adaptation. 24 The study concluded that adaptive planning can improve cumulative doses to OR, the therapeutic ratio, and the clinical results after the GTV decreases approximately 30% or more and if the decrease occurs within fractions of treatment. 24 Spoelstra et al 25 designed a prospective study to investigate the dosimetric consequences of tumor volume changes over time and used 4DCT scans to evaluate the possibility of plan adaptation in lung cancer patients. The study followed 24 patients who all received a course of chemotherapy in conjunction with RT. Each patient underwent 2 4DCT scans, one for the initial RT planning and the second was completed after the patient received a dose of 30Gy and approximately 3 weeks of chemotherapy. The new PTV generated after a dose of 30Gy of chemo-radiation was compared with an initial PTV that was created from select 4DCT phases. The results of this prospective study stated that 15 patients had an average PTV reduction of 8% after 30Gy. However, the PTV increased in 6 patients, with one patient s PTV increasing dramatically. In addition, the study also reported no change in the mean 95% isodose coverage among all patients. The study also reported total lung volumes after 30Gy both increased and decreased and the V 5, V 20, and MLD did not significantly change after 30Gy. Finally, the study reported that one patient needed re-planning due to disease progression during the course of RT. The PTV actually increased 39% in size which could have resulted in a dosimetric target miss. It was concluded that ART and 4DCT scanning have a limited role in lung cancer patients undergoing conventional radiotherapy. 25 The conclusions of this study are contrary to a previous study conducted by Fox et al 20 which reported significant GTV reductions of 30% by a dose of 30Gy. Fox et al 20 concluded that NSCLC patients would benefit from an ART approach which could escalate dose to the tumor volumes and minimize dose to OR. Barker et al 26 conducted a study that employed CTOR imaging to assess the anatomical changes in patients receiving RT for head and neck cancer. This study followed 15 patients with head and neck cancer that employed a CTOR system to scan patients 3 times per week. Each patient averaged CTOR scans throughout their course of RT. A GTV and normal tissues such as the parotid glands, spinal canal, and mandible were contoured on each CTOR scan by one RO to limit inter-observer variations in contouring. Linear regression analysis was used to calculate the rate of volume change over time for the GTV and parotid glands. To analyze the

25 25 positioning throughout RT, the C2 vertebral body was contoured on every CT scan using the Philips Pinnacle3 TPS and the center of mass of this structure was calculated on every CT scan. The C2 center of mass enabled a single point to be used as a common reference for all evaluations of positional change among the GTVs and normal tissues over time. The researchers of this study calculated the change in the center of mass of the parotid glands relative to a single external volume CT slice at the bone reference of C2 in the medial and lateral directions. The results of this study demonstrated that the GTV decreased at a median rate of 1.8% per day in comparison with the initial GTV and the center of this volume decreased asymmetrically. At the end of RT, the GTV reduced roughly 70% from the initial GTV. The study also stated the parotid glands decreased, as a result of patient weight loss from RT, with a median volume decrease of 0.19 cm 3 per day or 0.6% per day. The total median parotid volume decrease was 28.1% compared to the initial volumes. An interesting observation was pointed out in this study: patient weight loss and the decrease in volume of the parotid glands actually shift the center of these glands medially into the high dose region being treated in the patient. In addition, the investigators inferred that ART may be needed after a certain amount of weight loss experienced by the patient due to significant tumor volume reductions and the medial displacement of the parotid glands. This study concluded that ART may be needed to account for the measureable anatomic changes that occurred in the targets and critical structures after 4 weeks or RT. 26 Ahn et al 27 reported the results of a study on an ART protocol to assess the anatomic changes and positional variability during IMRT for head and neck cancer. In the study, 23 patients had an initial planning CT scan followed by repeat CT scans on the 11th, 22nd, and 33rd fraction of RT. These repeat CT scans were assessed for anatomical and positional changes to determine if these changes warranted an adaptation to the patients RT course. All patients were re-scanned on fraction number 11, number 22, and number 33 with radiopaque fiducial markers placed at the treatment isocenter. All GTVs and PTVs, as well as the OR were reconstructed on each re-scanned CT data set. The OR were adjusted by a RO to account for the patient s anatomical or positioning changes compared to the initial planning CT scan. The GTV and PTV were adjusted only if tumor volume shrinkage was evident at the primary site of the tumor. The original treatment fields for each patient were fused onto each re-scan CT data set according to the isocenter and bony anatomy. The radiation doses were re-calculated and a dose volume histogram (DVH) was generated for the re-contoured structures. Patients were re-planned if the constraints to the OR were not met or if the prescription dose coverage to the target volumes

26 26 were inadequate. The results of this study observed 15 of 23 patients (65%) benefitted from adaptive planning due to increased dose sparing to the OR and an improved dose distribution to the target volumes. The study concluded that no single anatomical change and positional variability change, such as weight loss, fraction number, or skin separations, can reliably predict the need for ART. The researchers concluded that it is important to use IGRT to monitor anatomy and positional variability during the patient s course of RT to decide to re-plan. 27 Renaud et al 28 conducted a study that employed megavoltage CT scans to determine the ART benefits in mesothelioma patients who received RT treatment with helical tomotherapy. By utilizing the Tomotherapy Planned Adaptive software, the variations of GTV, PTV 1 and 2, and OR contours on daily megavoltage CT scans could be evaluated. Two strategies for adapting the radiotherapy plan were investigated. The first strategy focused on reducing dose and improving sparing to OR and the second strategy concentrated on dose escalation to the GTV while maintaining normal tissue sparing. In addition, IMRT and 3DCRT plans were generated and used for comparison to the helical tomotherapy plan. In the first strategy, GTV reduction was observed after 22 fractions and the PTV margins were reduced by 4 mm which decreased the MLD by 19.4%. 28 The results from the dose escalation strategy reported the prescribed doses were increased from 50.0Gy to 58.7Gy in PTV 1 and from 60.0Gy to 70.5Gy in PTV The study also compared the IMRT plan and the 3DCRT plan results with the helical tomotherapy plan and reported that the IMRT plan spared normal tissues better than the helical tomotherapy plan but, lacked adequate tumor volume coverage. For the IMRT plan, the D 30 of the heart was reduced by 40% and the V 20 of the total lung volume was reduced by approximately 10%. However, the D 99 and D 95 of both PTV s were lower than the helical tomotherapy plan. The 3DCRT plan and the helical tomotherapy plan were both comparable in target coverage and normal tissue sparing. The D 30 of the heart was reduced by approximately 45% and the total lung volume V 20 was lowered by 5% in the 3DCRT plan. However, the spinal cord dose was a limiting factor in the 3DCRT plan and it was too high to be clinically acceptable. The conclusions from this study re-affirm that dose escalation and normal tissue sparing can be achieved by ART. 28 As previously stated, IGRT technologies have advanced and enabled the use of ART strategies in many types of cancer patients. The use of IGRT technologies can be beneficial for lung cancer patients in assessing tumor volume changes, tumor volume reductions, and anatomical or positional changes during the patient s course of RT. These technologies enable

27 27 ART strategies to be incorporated into a patient s RT regimen to account for these changes in order to deliver precise RT and minimize dose to normal tissues. Adaptive radiotherapy improves the accuracy of RT considerably and with improved accuracy, dose escalation to the tumor volume is achievable without compromising on limiting the dose to the OR. 2 Effects of Respiratory Motion in RT of NSCLC Mechalakos et al 29 conducted a study to assess the effects of free-breathing motion on GTV and PTV treatment margins in patients undergoing RT for NSCLC. This study evaluated 12 patients who incorporated free-breathing motion obtained from an independent analysis of fluoroscopic studies of the diaphragm in 7 patients. The study examined the effect of simulated breathing motion and setup uncertainties incorporated onto an original treatment plan. The component of breathing motion was incorporated in the treatment plans slice by slice. 29 The intrafractional breathing motion was incorporated by averaging the dose calculation over all displacements of the respiratory cycle. 29 In this study, the GTV volumes had a margin of 1-2 cm added to generate a PTV margin in the original plan. Additional components were modeled into the original treatment plan to model breathing motion and setup uncertainty. A setup error component, a breathing motion component, and an intrafractional breathing component all added additional margins onto the original treatment plan. The results of this study indicated that GTV with volumes of 60 cm 3 or more show a stronger sensitivity to breathing especially if the tumor shape is irregular. The effects of normal breathing on PTV margins are small with a 4% or less chance of a 10% or greater decrease in dose to the GTV. 29 The conclusions from this study indicated special consideration should be observed in patients with irregular tumors treated with the free-breathing technique and efforts such as respiratory gating should be considered to reduce breathing motion for patients with large respiration-induced motion. 29 van Sörnsen de Koste et al 30 conducted a study to characterize the 3D movement of lung tumors from multiple spiral CT scans in patients with stage I NSCLC. The multiple CT planning scans were comprised of 3 rapid scans and 3 slow scans. A total of 29 data sets were analyzed. All CT scans were co-registered with the GTVs contoured on each of the CT data sets which automatically propagated onto the initial treatment planning CT scan. A CTV was generated by adding a 5 mm margin on the GTV contour to account for microscopic tumor extension. An optimal CTV which encompassed all 6 CTVs for each patient was generated and was representative of the tumor position during respiration. This study reported that the location of the tumor within the different lobes of the lung did not correlate with mobility in x, y, and z

28 28 directions. The study also concluded that slow CT scans capture most of the tumor mobility during respiration for peripheral lung tumors. 30 Britton et al 31 reported on the changes in size, shape, and motion of the GTV and ITV utilizing 4DCT during radiotherapy in 8 patients with NSCLC. In the study, patient simulation was done with a 4DCT scan initially and then a 4DCT scan was completed every week until the RT course was complete. In each 4DCT data set, contours of GTVs, CTVs, and ITVs were delineated. The primary tumor volume was considered the GTV, the CTV was an expansion of the GTV by 8 mm to account for microscopic disease, and the ITV was created to encompass the CTVs. The center of the GTVs and ITVs served as the reference for motion analysis. The data from this study reported that tumor volume reduction on the 4DCT scans varied from 20% to 71% at the end of inspiration and 15% to 70% at the end of expiration. 31 Tumor mobility increased in the superior-inferior direction and the anterior-posterior direction. 31 Tumor motion was significantly greater in the superior-inferior direction compared to all other directions. The conclusions drawn from this study indicated that repeat 4DCT scans may be warranted to quantitatively assess tumor changes and respiratory tumor motion during radiotherapy treatment. Burnett et al 32 assessed the most effective way to manage lung tumor motion in patients undergoing radiotherapy treatment for lung carcinoma. This study utilized a formula that combined tumor motion measurements and setup errors in 7 patients to determine adequate PTV margins for treatment using data from previous studies. This study compared individualized PTV margins to those PTV margins obtained through motion management. The percent volume of the lung receiving 20Gy or V20 was analyzed. The study concluded that any form of motion management used to derive PTV margins is more beneficial than using a standardized PTV margin. 32 The benefits of gating compared to ungated PTV margins demonstrated a modest advantage unless the tumor is highly mobile. 32 Li et al 33 conducted a study to compare the positional and volumetric differences of PTVs based on axial 3DCT and 4DCT scans for NSCLC tumors. 33 This study consisted of 28 patients diagnosed with NSCLC. Each patient underwent an axial 3DCT scan followed by a 4DCT freebreathing scan. During the 4DCT scan, images were reconstructed in 10 respiratory phases and GTV was delineated on each of the 10 respiratory phases. The extent of the GTV center was measured in each of the 10 respiratory phases and a 3-dimensional vector was calculated. This PTV vector was defined by the GTVs contoured on the 3D image set using the individual tumor motion measured on the 4DCT scan. 33 Whereas, a PTV 4D was generated from the motion of the

29 29 CTVs on all phases of the respiratory cycle on the 4DCT scan. In addition, this study categorized these 28 patients into 2 separate groups. Group A, which consisted of patients whose lesions were in the upper lobe of the lung and Group B, which represented patients whose lesions were in the middle or lower lobes of the lung. The differences in target position, volume, and coverage between PTV vector and PTV 4D were evaluated for tumors in different lobes. 33 The results of this study indicated that the average motion for tumors in Group A was 2.8 mm and Group B was 7 mm. The motion of cranial-caudal direction is larger in Group B than for Group A. The conclusions drawn from this study indicated that 3DCT based PTVs, which represent tumor motion, encompass large normal tissue volumes, especially in Group B, and should not be used in treatment planning. 33 Brock et al 34 compared lung dosimetry parameters between a free-breathing treatment plan and an ABC treatment plan and also evaluated the feasibility and reproducibility of an ABC in patient undergoing radiotherapy for NSCLC. This study reported 18 patients underwent a freebreathing CT scan and were instructed to breathe normally. In addition, a nose clip and an ABC mouthpiece with an air flow measurement device was attached to the patients and 3 CT scans for each patient were acquired. In each CT scan the patient was instructed to breath hold at 70% lung inspiration capacity measured by the ABC device. The visible tumor and lymph nodes made up the GTV which was delineated on both the ABC and free-breathing scans. The PTV was generated by expanding the GTV by 1.0 cm axially and 1.5 cm in the superior-inferior direction. In addition, OR were contoured on each scan and included the spinal cord, normal lung minus GTV, heart, and esophagus. This study evaluated lung volumes, the percentage of lung volume treated at 20Gy (V 20 ), and MLD between each plan. The results of this study reported that all but one patient was able to complete radiotherapy using ABC daily. The average reduction in GTV was 25% from planning to the end of treatment. The ABC plan reduced the V 20 by 13%, V 13 by 12% and the MLD by 13% when compared to the free-breathing plan. Furthermore, the conclusions from this study indicated that ABC is well tolerated by patients and using ABC reduces the dose-volume parameters in lung toxicity which may allow for dose escalation. 34 Panakis et al 35 further evaluated ABC and its effect on physical lung parameters. The findings reported that the MLD was reduced by 25%, the V 20 was reduced by 21%, and the V 13 was reduced by 18% compared to free-breathing plan in their study sample. These findings support the study done by Brock et al 34 that ABC is tolerable for NSCLC patients, PTV margin reduction can spare normal lung, and dose escalation may be achieved. 35

30 30 The ability to evaluate, quantify, and manage respiratory motion in the treatment of NSCLC is an integral part of the ART process. Image-guided radiation therapy technologies evaluate the changes in sizes of tumor volumes, the positions of tumor volumes, and tumor volume respiratory motions throughout the course of radiotherapy. These are all key components of the adaptive planning process. The respiratory motion management of lung tumors can facilitate better patient outcomes in RT treatments. All of the previously stated respiratory motion techniques continue to benefit patients with NSCLC and will advance ART strategies in the treatment of lung cancer. Trends in ART of NSCLC Lim et al 17 analyzed rccbct in 60 patients to evaluate the tumor size, shape, and location during radiotherapy for NSCLC. Each patient underwent a KVCBCT that was used for patient positioning prior to treatment. The CBCT was reconstructed off-line using the position of the diaphragm into 10 data sets which produced a serial rccbct data set which was then registered with a 4DCT scan. In addition, the KVCBCT images collected off-line at fraction 1, 5, 10, 15, 20, 25, and 30 were reconstructed into a serial rccbct data set. The primary tumor volume was contoured on each fraction of the rccbct data set. The registration of the serial rccbct with the planning 4DCT data set represented the respiratory phase which could be evaluated for volumetric and positional tumor changes. More than 30% tumor regression was reported in 40% of the patients through mid-treatment and 67% by the completion of treatment. 17 This study also indicated greater tumor regression rates earlier in the radiotherapy treatment course. The study concluded that through the use of rccbct significant tumor regression was observed and that patients would benefit from ART. Bosmans et al 36 conducted a study investigating the changes in tumor volume, tumor motion, and breathing frequency during the first 2 weeks of an accelerated course of radiotherapy for NSCLC. The study evaluated 23 patients that were simulated for radiotherapy using a CT-PET simulator. The GTV was delineated from CT-PET data before treatment began. The CTV was defined as the GTV plus a 5 mm margin which represented microscopic disease and the PTV was defined as the CTV plus a 1 cm margin which represented internal respiratory motion and setup error. In addition, all patients also underwent a respiration-correlated CT scan that was reconstructed in 10 phases from 0% to 100%. This respiration-correlated CT scan represented the tumor motion in the respiratory phase. The tumor volume changes that this study reported during RT treatment were mostly moderate volume changes under 30%. Only 3 of 23

31 31 patients experienced a tumor volume decrease that was greater than 30% and 4 of 23 patients experienced a tumor volume increase greater than 30%. In addition, tumor motion and breathing frequency were reported to have no significant effect during radiotherapy. The study concluded that repeated CT-PET imaging is necessary during radiotherapy due to the large variability of changes in tumor volumes and respiratory correlated imaging during radiotherapy may not be necessary because changes in tumor motion are small. 36 The use of repeat imaging during the course of RT is necessary to assess the tumor volumes and adapt the patient s RT treatment plan. Weiss et al 37 conducted a study which analyzed tumor volume and tumor motion during respiration and also the respiratory relationship in volume and position of normal tissues utilizing 4DCT scans of 14 patients with lung carcinoma. Each patient underwent a respiration-correlated 4DCT scan where the respiratory cycle was recorded in 10 phases with T0 representing maximum inspiration, T5 representing the middle or 50% inspiration, and T9 representing maximum expiration of the respiratory cycle. The GTV and the spinal cord, esophagus, heart, lungs, trachea, and the diaphragm on the side of the tumor were contoured in all phases of the respiratory cycle. The structures were evaluated for volume changes relative to the respiratory cycle. The results of this study indicated that during the respiratory cycle, contoured volumes varied as much as 62.5% for GTV, 25.5% for lungs, and 12.6% for hearts. Also, during respiration the central positions of the normal tissues varied significantly from the central positions of the GTVs in individual patients. This study concluded that the central distance between the GTV and the center of the normal tissues during respiration may affect the discussion regarding which phase of the respiratory cycle allows for optimal normal tissue sparing. 37 This study also concluded that many uncertainties remain in interpreting the data 4DCT scans provide including tumor volume changes, positional variations of OR, as well as the position of the OR in reference to the tumor volumes. The use of autosegmentation tools and deformable image registration software will result in higher efficiency and use of 4DCT by reducing the contouring work and improving contour accuracy which will facilitate the use of ART in the treatment of NSCLC patients. 37

32 32 Chapter III: Methodology Advances in IGRT have propelled ART strategies to the forefront as a means of providing patients with the most accurate RT plans for many types of cancers. Adaptations in a patient s RT plan may be needed as result of tumor growth or regression, biological changes in anatomy or tumor volumes, and positional or localization changes observed during the course of RT. Various IGRT techniques and adaptive strategies may account for these changes, enable dose escalation, improve local control, as well as, overall survival for patients. 8 The purpose of this study was to present a single institution s experience in developing a purposeful and efficient off-line technique to incorporate ART in a clinical environment for the treatment of lung cancer. This chapter examines the sample selection and description of patients for this study, the instrumentation that was used, a description of how data was collected and analyzed, and a discussion of study limitations. Sample Selection and Description A purposive sampling technique was used to select patients for this study. The sample included 9 patients that have undergone RT for lung carcinoma at the UNMC. For this study, a retrospective review was conducted on 9 patients that were treated with external beam RT to the thoracic region and underwent a daily CTOR scan for localization prior to RT during the time frame of November 2009 to March of The sample selection was based on patients who were diagnosed with non-small cell lung carcinoma in various disease stages. Five patients received a prescription dose of at least 60Gy or greater and 4 patients received a preoperative prescription dose of 45Gy. Patient 1 A 45 year old female diagnosed with NSCLC of the left upper lobe of the lung and mediastinum, T3, N2, M0, stage IIIA. The patient had a significant smoking history of 1/2 pack to 1 pack a day for 30 years. The patient was referred to the radiation oncology department and the recommendation from the RO was for the patient to receive a definitive course or RT prescribed to 44Gy at 2Gy per fraction for 22 fractions with concurrent chemotherapy. Patient 2 An 81 year old female diagnosed with NSCLC of the right lung invading the hilum, chest wall and ribs, T3, N2, M0, stage IIIA. The patient had a significant smoking history of a pack a day for 70 years. The recommendation from the RO was a definitive course of RT prescribed to 70Gy at 2Gy per fraction for 35 fractions with concurrent chemotherapy. Patient 3 A 79 year old female diagnosed with NSCLC of the right upper lobe of the lung with pretracheal lymph node involvement, T2, N0, M0, stage IB. The patient denied any smoking

33 33 history however; her spouse had a 20 year smoking history. The recommendation from the RO was a definitive course of RT prescribed to 70Gy at 2Gy per fraction for 35 fractions. Patient 4 A 55 year old female diagnosed with NSCLC of the right lower lobe of the lung with mediastinal involvement, stage IIIB. The patient had a significant smoking history of 1½ packs per day for 27 years and stated she quit at age 42. The recommendation from the RO was a definitive course of RT prescribed to 60Gy at 2Gy per fraction for 30 fractions with concurrent chemotherapy. Patient 5 A 65 year old female diagnosed with NSCLC of the right lower lobe of the lung with mediastinal involvement, stage IIIA. The patient had a significant smoking history for the last 45 years and just recently quit. The recommendation from the RO was a definitive course of RT prescribed to 61.2Gy at 1.8Gy per fraction for 34 fractions with concurrent chemotherapy. Patient 6 An 80 year old male diagnosed with NSCLC of the left upper lung with mediastinal involvement, T1, N2, M0, stage IIIA. The patient had a smoking history dating back to his early twenties of 1 ½ packs per day for 30 years, but states he quit smoking approximately 25 years ago. The recommendation from the RO was a preoperative course of RT prescribed to 45Gy at 1.8Gy per fraction for 25 fractions with concurrent chemotherapy followed by surgery. Patient 7 A 63 year old male diagnosed with NSCLC of the left upper lobe of the lung with mediastinal involvement, T3-T4, N0, M0, stage IIIB. The patient had a smoking history of 1 pack per day for 20 years and quit smoking 27 years ago. The recommendation from the RO was a preoperative course of RT prescribed to 45Gy at 1.8Gy per fraction for 25 fractions with concurrent chemotherapy followed by surgery. Patient 8 A 57 year old male diagnosed with NSCLC of the left lung with mediastinal involvement, stage IIIA. The patient had a smoking history of 2 packs per day for 30 years and quit smoking 10 years ago. The recommendation from the RO was a preoperative course of RT prescribed to 45Gy at 1.8Gy per fraction for 25 fractions with concurrent chemotherapy followed by surgery. Patient 9 A 55 year old female diagnosed with NSCLC of the right lung with mediastinal involvement, stage IIIA. The patient had a smoking history of 1½ packs per day for 18 years and quit smoking 3 years ago. The recommendation from the RO was a preoperative course of RT prescribed to 45Gy at 1.8Gy per fraction for 25 fractions with concurrent chemotherapy followed by surgery. Instrumentation

34 34 This off-line ART technique utilized the Philips Pinnacle3 v.9.0 TPS and involved rigid image registration of the treatment planning CT data set to the CTOR data sets obtained from a Siemens Somatom Sensation Open CT scanner. This study was a retrospective review of 9 patient case studies who received RT for non-small cell lung carcinoma. Additional research included incorporating IGRT technologies with ART strategies of lung cancer patients. For each patient, an off-line ART re-planning technique was demonstrated using CTOR data sets and the original planning CT data sets. Observations and measurements of the changes in tumor volumes using this adaptive technique were compared in the TPS. The dose calculations by the TPS for volume and dose comparisons used in this study were achieved using the Adaptive Convolve Algorithm. Data Collection Data collected in this study consisted of tumor volume comparisons and measurements from the initial RT treatment data set and treatment plan to a CTOR data set on every 10th fraction of RT. The data collection began by assigning the 10th, 20th, and 30th (if applicable) CTOR data set as the primary data set in the TPS. Each of the 9 patients in this retrospective study had undergone a RT treatment planning CT scan in which the tumor volumes (GTVs and CTVs) and OR had been delineated by a RO and a RT treatment plan had been completed. The radiation doses for each of these 9 patients ranged from 45Gy to at least 60Gy and a DVH for each contoured structure was generated for the initial RT treatment plan. An image registration and fusion of a secondary CTOR data set to the initial treatment planning CT data set was performed on the TPS. Once this registration and fusion were validated for accuracy, tumor volumes from the initial treatment planning CT data sets were propagated onto the CTOR data sets. These tumor volumes were propagated onto the CTOR data sets for every 10th fraction. The initial propagated tumor volumes on the CTOR data sets were adapted to any tumor volume changes, tumor volume reductions, or anatomical changes and measured in reference to the initial tumor volumes. During the transfer process of the tumor volumes on the CTOR scans, there was minimal distortion of the tumor volumes that occurred between initial treatment planning and the CTOR data sets. The volumes of the transferred GTVs and CTVs on the CTOR data sets could be enlarged or reduced due to the translation between the two data sets. The GTVs demonstrated visible disease and the CTVs were non-uniform expansions from the adapted GTVs based on the discretionary expertise of the RO. The CTVs were modified based on the reduction of microscopic disease. The measurement of tumor volume changes due to RT

35 35 treatment (expansions or reductions) and any dosage changes to the tumor volumes were analyzed. The first comparison (comparison I) analyzed tumor volume changes between the CTOR data sets and the initial RT treatment data sets to determine a 5% or greater change in each of the 9 patients. Tumor volumes were computed from statistics in the regions of interest location in the TPS. These volumes were recorded in cm 3 for the initial RT treatment data sets and adapted tumor volumes in the CTOR data sets. Each CTOR tumor volume was compared and analyzed to the initial RT tumor volume to determine if a 5% or greater change had taken place. For comparison II, DVHs were used to analyze the relationship between normal tissues and the adjacent CTVs in the 10th, 20th, and 30th (if applicable) and the last fraction to determine the percent change in the normal tissues compared with the normal tissues and CTVs from the initial RT treatment plans. For patients 1, 4, 5, 7, and 9 that demonstrated a 5% or greater tumor volume change as demonstrated in comparison I, the initial RT treatment fields and beam parameters were re-constructed onto each CTOR data set using a hotscript in the TPS. The initial RT treatment plan isocenter was manually placed on each CTOR data set within the propagated tumor volumes and verified for accuracy visually with an orthogonal pair of DRR s of the patient s anatomy by a medical dosimetrist. The initial RT treatment beams were computed by the TPS on each CTOR data set and the monitor units were set for each beam. Normal tissue was contoured on each CTOR data set and each adapted tumor volume on the CTOR was removed from the normal tissue. The normal tissue was adjacent to the adapted tumor volume in each CTOR data set. A DVH was generated to analyze the percent change in the normal tissue on the 10th, 20th, and 30th (if applicable) and the last fraction in relation to the initial RT treatment plan normal tissue. On each DVH the radiation prescription dose from each fractionation interval was specified in the max dose location on the DVH for 100%, 95%, 90%, and 80%. The normal tissue percentage in relation to prescription dose was generated from the DVH and recorded. This data represented the percentage of normal tissue excluding the tumor volume at specified radiation doses for specific fractionation intervals. In comparison III, 3DCRT and IMRT techniques were evaluated which incorporated data that was collected in comparison II to determine which patient demonstrated the most significant normal tissue changes at 100% prescription dose. Patients 1, 7, and 9 each had 3DCRT reconstructed treatment plans while patient 4 and patient 5 each had re-constructed IMRT treatment plans. Data from each of these patients was recorded and analyzed.

36 36 Data Analysis The retrospective patient reviews compared data sets obtained from a CTOR system to the initial planning CT data sets used in the patients RT plan on the 10th, 20th, and 30th treatment fraction. As stated above, the tumor volumes were analyzed by comparing the treatment planning CT data set volumes to the CTOR data set volumes and measuring the changes of the target volumes. These measurements were reported as percentage deviations compared to the original RT treatment plan. In addition, dose changes and tumor dose coverage on the target volumes were assessed. An adaptation of the initial RT plan due to these changes in tumor volume, shape and position was done. The intent was to measure the target volumetric changes in anticipation that the target volume and treatment margins would significantly change and adapt the patients RT to these changes. Overall, these reductions should benefit the patients RT treatment by allowing for tumor dose escalation, limiting the toxicities from RT, and hopefully gaining a better long term outcome. Limitations The limitations of this study included the possibility of positional and rotational inaccuracies in the image registration based on inter-observer variations. These variations may affect the tumor volume propagation of the original tumor volumes onto the CTOR data sets. Inaccurate image registrations of multiple data sets may introduce errors into the contours that are propagated onto the CTOR data sets from the original CT treatment planning data sets. Another limitation of this study included the inter-observer variations of tumor volumes and tumor volume responses to radiation. The segmentation of tumor volumes and the determination of whether or not a tumor volume responded to RT was completed and reviewed by 2 ROs and may be subject to interpretation. Additional limitations included tumor volume responses from neo-adjuvant or concurrent chemotherapy agents introduced prior to or during RT treatments, truncated CTOR scans which limit the anatomy that could be analyzed for this study, and also the influence of the patients respiratory motion and its effects on the delineation of the tumor volumes. A final limitation included the accuracy in which the marker BBs were placed on the patient s treatment isocenter prior to CTOR scans. The marker BBs corresponded to the patient s treatment isocenter and inaccurate placement of these BBs on the CTOR scan may have introduced inaccuracy in transferring the radiation beams onto the CTOR data sets. Summary

37 37 This retrospective study presented a single institution s experience with an off-line ART technique using a CTOR system. The retrospective study compared data sets obtained from a CTOR system to the initial CT data sets used in the patient s RT plan on the 10th, 20th, and 30th (if applicable) treatment fraction. These data sets were analyzed to assess tumor volume changes and develop an off-line ART technique. Comparison I utilized a criteria of 5% or greater tumor volume change to evaluate 9 patients for off-line ART. Comparison II used the patients that demonstrated a significant change in tumor volumes from comparison I to analyze the percent change in normal tissues and adjacent CTVs in the 10th, 20th, and 30th (if applicable) and the last fraction to the normal tissues and CTVs in the initial RT treatment plans. Comparison III evaluated the 3DCRT and IMRT techniques of the patients that underwent a significant tumor volume change from comparison I to determine which patient and what type of RT treatment technique reported the most significant normal tissue changes. The data collected from each of these 3 comparisons in this study was used to conclude if this off-line ART technique is purposeful, practical, and efficient in order to benefit lung cancer patients at UNMC.

38 38 Chapter IV: Results The goal of this study was to develop a purposeful and efficient technique to incorporate ART in a clinical setting for the treatment of lung cancer. The purpose of this study was not only to implement a simple off-line ART technique that is practical and efficient to use for adaptation of RT plans, but also to produce a more conformal treatment plan through adaptation during the patient s course of treatment. In this study, the initial planning CT data sets for 9 patients treated for lung carcinoma were compared to CTOR data sets from the 10th and 20th fraction of RT for possible tumor volume changes. Three of 9 patients compared the CTOR data sets from the 30th fraction of RT to their initial planning CT data sets for possible tumor volume changes. Tumor volumes from the initial treatment planning CT data sets, which included a GTV and/or a CTV, were compared to the CTOR data sets on the 10th, 20th, and 30th treatment fractions to evaluate volumetric changes. The results of this study demonstrate the significance of precise image registration when combining different data sets, the accuracy of contour propagation between different data sets, and the impact inter-observer variations have on contouring tumor volumes between different data sets. Item Analysis The results of this study were divided into 3 comparisons which demonstrated tumor volume changes between CTOR data sets and the initial planning CT data sets. A tumor volume change of 5% or greater in any of the CTOR data sets indicated a definitive change in the tumor volumes among patients throughout their course of RT. For comparison I, 9 patient tumor volumes were analyzed on the 10th, 20th, and 30th (if applicable) fractionation intervals for a 5% or greater overall change which indicated a significant response in the GTVs and/or CTVs to RT. For comparison II, the patients that demonstrated tumor volume changes were analyzed individually to assess the amount of tumor volume response in relation to normal tissue on the 10th, 20th, and last fraction of RT. For this comparison, the adapted CTVs and the amount of normal tissue covered by 100%, 95%, 90%, and 80% of the prescription dose were compared on the 10th, 20th, and last fraction of RT to the original CTVs and normal tissues at the beginning of the patient s RT. In comparison III, the techniques of IMRT and 3DCRT and the tumor volume changes associated with each were analyzed to determine if significant tumor volume change was prevalent in one or both techniques. For this comparison, the original GTVs and CTVs from the patient s initial treatment planning data set were exported and propagated onto the 10th, 20th, and 30th (if applicable)

39 39 CTOR data sets in the TPS. The GTVs and CTVs were reviewed by one of 2 ROs to assess tumor volume responses in each of the fractionation intervals. If a response in the tumor volumes were indicated, the RO adjusted the original GTV and CTV on the CTOR data sets. The actual size of each tumor volume was computed in the TPS and reported as cm 3 for the original GTVs and CTVs plus any subsequent changes made to each of these volumes in the fractionation intervals. The tumor volume changes that were completed in the 10th, 20th, and 30th (if applicable) fractions were computed and reported in cm 3 and compared against the original GTV and CTV values. The percent change between the original GTV and CTV values and the corresponding values in the fractionation intervals were reviewed and analyzed for 9 patients. The results for the overall GTV and CTV changes for the 9 patients from the initial RT fractionation to the 20th or 30th fractionation were analyzed and reported (Table 1). From the sample population, 6 patients had both a GTV and CTV defined by a RO as regions of interest, while 3 patients had only a single GTV or CTV as a region of interest defined by a RO. The average percent change and standard deviation was computed in the sample population for patients with GTVs and in patients with CTVs and patients with both GTVs and CTVs. The average percent change in the GTV for 7 out of 9 patients recorded from the initial fraction through the 20th fraction resulted in a tumor volume reduction of 19.7%. The average percent change in the CTV for 8 out of 9 patients from the initial fraction through the 20th fraction resulted in a tumor volume reduction of 12.8%. The results for the GTV and CTV changes in the overall treatment of RT in the sample population are shown in Figure 1. This comparison revealed that 56% or 5 of 9 patients demonstrated significant tumor volume changes in either the GTVs or CTVs of 5% or greater during a course of RT. The data collected in comparison I was further analyzed to include the percentage of change in the GTVs and CTVs in the 10th fraction, 20th fraction, and the 30th fraction (if applicable) for the 5 patients that underwent significant tumor volume changes. The percentage of GTV change over 20 fractions was evaluated for patients 1, 5, 7, and 9, while patient 4 was evaluated over 30 fractions. Patient 9 demonstrated the highest percentage of GTV reduction of 30.7% by the 10th fraction and a 28.9 % reduction from the 10th fraction to the 20th fraction. Patient 9 exhibited the most GTV reduction from the initial fraction to the 20th fraction compared to the other 4 patients. Patient 1 had the lowest percentage of change in the GTV by the 10th fraction and had a slight increase in tumor volume from the 10th to the 20th fraction. From the initial fraction to the 20th fraction, patient 1 reported an increase in the GTV of 0.64%

40 40 which demonstrated very slight GTV growth and no tumor volume reduction compared to the other 4 patients. The RT plan for patient 4 represented the GTV reduction after a completed RT treatment plan. This patient s GTV reduction by the 30th fraction was 36.8% which resulted in the second highest overall GTV reduction throughout the course of treatment. Analysis of the percentage of CTV change on the 10th and 20th fractions was also evaluated on the patients 1, 5, 7, and 9, while patient 4 was evaluated over 30 fractions. Patient 9 exhibited the greatest percentage of change by the 10th fraction with a 22.4% reduction in the CTV. However, patient 1 had the greatest percentage of change from the 10th to the 20th fraction and from the initial fraction to the 20th fraction with a CTV reduction of 30.8% and 30.7% respectively. In contrast, patient 1 also had the lowest percentage of change in the CTV by the 10th fraction which demonstrated a slight increase in the CTV. In addition to the GTV analysis, patient 4 had a CTV reduction of 15.1% from the initial fraction to the 30th fraction. The results of the tumor volume changes by fractionation intervals for these 5 patients can be seen in Figure 2. Comparison II utilized DVHs to analyze the percent change in the initial normal tissues and initial CTVs in patients 1, 4, 5, 7, and 9 RT treatment plans. These volumes were compared to the adjusted normal tissues and adjusted CTVs at the 10th, 20th, and 30th (if applicable), and the last fraction. The analysis for comparison II evaluated the percent changes from the prescription doses generated from the DVHs for the normal tissues adjacent to the CTVs for each patient from the original RT plan throughout the fractionation intervals. The basis for this comparison utilizing normal tissues is the relationship of the normal tissues adjacent to the CTVs. Theoretically, if the adjusted CTVs demonstrate a reduction in volume then the normal tissue volumes and doses at specific fractionation intervals should increase. However, if the normal tissue volumes and doses at specific fractionation intervals decrease compared to the original values, then the adjusted CTVs may not demonstrate a reduction in volume. The data for comparison II utilized radiation beams from each patient s initial RT plan and transferred those beams onto the 10th, 20th, and 30th (if applicable) CTOR scans. The beam isocenters were verified on each CTOR scan from marker BBs placed at the treatment isocenter on each patient. The monitor units for each radiation beam were set manually in accordance to the original RT plan. Each CTOR scan on the 10th, 20th, and 30th (if applicable) fraction had the radiation beams and monitor units from the patient s original RT treatment plan. Doses were computed on each CTOR scan and compared to the original treatment plans. The normal tissue was contoured

41 41 on each CTOR scan and DVHs were generated to calculate the percent change in normal tissues between all plans at specified prescription doses. Analyzing certain doses to normal tissues to evaluate and compare the adjusted CTVs on the fractionation intervals and the last fraction to the original treatment plans represented tumor volume response. Comparison II analyzed the relationship between normal tissues and the adjusted CTVs in the 10th, 20th, 30th (if applicable) and the last fraction to determine the percent change in the normal tissues compared to the normal tissues and CTVs from the initial RT treatment plan. Patient 5 demonstrated the greatest percent change in the normal tissues at 100%, 95%, 90%, and 80% of the prescription dose at each fractionation interval. Both patients 5 and 9 exhibited positive normal tissue percent changes in each fractionation interval which demonstrated a reduction in the CTVs and an increase in prescription dose to the normal tissues. Patient 4 had a 27.4% normal tissue increase on the 30th fraction at 100% of the prescription dose but, on the 10th and 20th fraction reported a -5.1% and a -2.2% normal tissue decrease respectively. Conversely, patient 7 had the greatest normal tissue decrease of -9.9% on the 10th fraction but, on the 20th and 25th fraction exhibited a 1.5% and 1.7% normal tissue increase respectively. Patient 1 had a normal tissue increase at 100% of the prescription dose on the 10th, 20th, and 25th fraction with the highest percent change 8.3% on the 25 th fraction. However, on the 10th, 20th, and 25th fraction a normal tissue decrease was reported at the 95%, 90%, and 80% prescription dose levels. The results for this comparison can be seen in Figures 3, 4, 5, 6, and 7. Comparison III evaluated the 3DCRT and IMRT techniques comparing the tumor volume changes in each. The data in comparison III incorporated the percent change in normal tissues from comparison II to determine which patient demonstrated the most significant normal tissue changes at 100% prescription dose on the 10th, 20th and last fractionation. When comparing patients 1, 4, 5, 7, and 9, patients 4 and 5 had IMRT treatment plans and patients 1, 7, and 9 had 3DCRT treatment plans. Patient 5 exhibited the greatest normal tissue increase at 100% of the prescription dose in all fractionation intervals. Patient 4 demonstrated the second greatest normal tissue increase of 27.4% in the 30th fractionation. Patients 4 and 5 demonstrated the greatest normal tissue increase on the last fractions of their individual adapted RT plans which corresponds to a reduction of the CTVs. Patients 1, 7, and 9 exhibited a modest normal tissue increase on the 20th and last fraction of each adapted plan. The greatest CTV reduction was demonstrated in patient 9 with a normal tissue increase of 18.1% in the 20th and last fraction of the adapted plan. The results for this comparison can be seen in Figure 8.

42 42 The results from these comparisons demonstrated that over one half of the patients sampled had significant tumor volume responses in either the GTVs, CTVs or both volumes within the 10th to 20th fraction of RT. In addition, patients have shown tumor volume responses in the GTVs and CTVs as early as the 10th fraction of RT. However, the data suggested that tumor volume responses in both the GTVs and CTVs in any fractionation interval are random and unpredictable. The data presented no identifiable trends in tumor volume responses in the 10th and 20th fractionation intervals which indicated the need for adaptation of the original treatment plan. The data also suggested that the percent change in normal tissues corresponding with adjusted CTVs at certain fractionation intervals are unpredictable and in some instances demonstrated no CTV reductions when attempting to adapt the original RT plan. Measuring the percent change in normal tissues at prescription doses corresponding to the fractionation intervals did not indicate identifiable trends for adapting the original treatment plan prior to the 20th fraction. Finally, the data suggested that the IMRT technique offered a greater percent change in normal tissues corresponding with greater CTV reductions in fractionation intervals greater than 20.

43 43 Chapter V: Discussion The purpose of this research was to develop a purposeful and efficient off-line technique to incorporate ART in a clinical environment for the treatment of lung cancer. This study provided important considerations when developing, evaluating, and incorporating an ART technique into a clinical environment for lung cancer. Analysis of the adjusted tumor volumes on the CTOR scans on the 10th, 20th, and 30th (if applicable) fractions demonstrated that significant tumor volume changes were occurring by the 10th and 20th fractionation intervals. The results of this study indicated that greater percent changes to the normal tissues from the prescription doses at certain fractionation intervals corresponds to decreasing tumor volumes and increasing tumor volume responses to RT. The data from the study suggested that both tumor volume reductions and increasing doses to normal tissues are random and adapting the patient s original tumor volumes from the initial RT plan on the CTOR scans at the 10th and 20th fractionation may be unpredictable. Limitations The limitations of this study include the possibility of positional and rotational inaccuracies in the image registration based on inter-observer variations. These variations may affect the tumor volume propagation of the original tumor volumes onto the CTOR data sets. Inaccurate image registrations of multiple data sets may introduce errors into the contours that are propagated onto the CTOR data sets from the original CT treatment planning data sets. Another limitation of this study includes the inter-observer variations of tumor volumes and tumor volume responses to radiation. The segmentation of tumor volumes and the determination of whether or not a tumor volume responded to RT was completed and reviewed by 2 RO s and may be subject to interpretation. Additional limitations include tumor volume responses from neo-adjuvant or concurrent chemotherapy agents introduced prior to or during RT treatments. Other limitations of this study include truncated CTOR scans which limit the anatomy that could be analyzed for this study and also the influence of the patients respiratory motion and its effects on the delineation of the tumor volumes is beyond the scope of this research study. A final limitation includes the accuracy in which the marker BB s are placed on the patient s treatment isocenter prior to CTOR scans. The marker BB s correspond to the patient s treatment isocenter and inaccurate placement of these BB s on the CTOR scan may introduce inaccuracy in transferring the radiation beams onto the CTOR data sets. Conclusions

44 44 The research and analysis of this study was conducted to develop a purposeful and efficient off-line technique to incorporate ART in a clinical environment for the treatment of lung cancer. The analysis of the data in this study corresponded to the previous research conducted that incorporated multiple CT scans during the course of RT to assess the possibility of reducing treatment volumes. Previous research concluded that greater tumor volume changes occurred at the front part of a course of RT when a patient reached a dose of 30Gy and that these changes could not be used as a prediction model for the remainder of the RT treatment. The significance of tumor volume regression throughout the course of RT remains questionable. The results of the comparison I study indicated that over one half of the patients sampled exhibited a significant tumor volume response of 5% or greater between the 10th and 20th fraction. In addition, average percent change for patients with a GTV between the 10th and 20th fraction demonstrated a 10.5% reduction in volume. Patient 4 had an average GTV reduction of 24.5 % between the 20th and 30th fraction. Patients with a CTV between the 10th and 20th fraction reported an average percent change of 7.9% between the 10th and 20th fraction. Comparison II analyzed the relationship between normal tissues and the adjusted CTVs in the 10th, 20th, 30th (if applicable) and the last fraction to determine the percent change in the normal tissues compared to the initial treatment plan normal tissues and CTVs. The data in this comparison was used to indicate potential treatment plan adaptation if a significant increase in normal tissue was indicated. A significant increase in normal tissue on the CTOR scans would correspond to a significant reduction in the CTV. Patient 5 demonstrated the greatest percent change in the normal tissues at 100%, 95%, 90%, and 80% of the prescription dose at each fractionation interval. Patient 5 and Patient 9 both exhibited positive normal tissue percent changes in each fractionation interval which demonstrated a reduction in the CTVs and an increase in prescription dose to the normal tissues. The results in the comparison were unpredictable with an unexpected number of patients having normal tissue volumes less than the original normal tissue values from the initial plan. The results actually demonstrated a decrease in normal tissue volumes on the CTOR scans at different fractionation intervals. Patient 4 had a 27.4% normal tissue increase on the 30th fraction at 100% of the prescription dose but, on the 10th and 20th fraction reported a -5.1% and a -2.2% normal tissue decrease respectively. In addition, patient 7 had the greatest normal tissue decrease of -9.9% on the 10th fraction but, on the 20th and 25th fraction exhibited a 1.5% and 1.7% normal tissue increase respectively. The

45 45 conclusion regarding this ART technique is that is unpredictable and may not be an accurate technique to adapt RT treatment plans in patients with lung cancer. Comparison III analyzed the 3DCRT and IMRT techniques comparing the tumor volume changes in each technique by incorporating the data from comparison II. The data demonstrated that the IMRT technique offers a greater percent change in normal tissues corresponding with greater CTV reductions in fractionation intervals greater than 20 when compared to the 3DCRT technique. Patient 5, an IMRT patient, exhibited the greatest normal tissue increase at 100% of the prescription dose in all fractionation intervals. Patient 4, also an IMRT patient, demonstrated the second greatest normal tissue increase of 27.4% in the 30th fractionation. Patients 4 and 5 demonstrated the greatest normal tissue increase on the last fractions of their individual adapted RT plans. The results in this comparison were also unpredictable since the data from comparison II exhibited normal tissue decreases from the initial values. However, in the overall comparison of 3DCRT versus IMRT techniques, the patients with IMRT techniques experienced greater CTV reduction at higher fractionations. The conclusions from this study have demonstrated that developing a purposeful and efficient off-line technique to incorporate ART in a clinical environment for the treatment of lung cancer needs further investigation. Inaccurate image registration of multiple data sets may introduce errors and effect the original tumor volume propagation onto the CTOR data sets. Other factors may introduce errors into the ART process that may contribute to the overall unpredictability of the tumor volume response that was demonstrated in this ART technique. Without further investigation and a reduction in the uncertainties in this ART technique, this technique is inefficient and does not yield adequate or consistent results in tumor volume reduction to further explore implementing this technique in a clinical environment. Recommendations The results from this study demonstrated that tumor volume responses are largely random and too unpredictable to incorporate this ART technique into a clinical environment for the treatment of lung cancer. It is important to note that a patient s response to RT provides the biggest uncertainty and finding a technique to predict tumor volume reductions are still being researched extensively. The limitations of this study introduced a significant amount of uncertainty and procedural error into this technique, making it unsuitable for use as an ART technique. Further investigation into technologies, such as deformable image registration systems, should be done to address image registration and image segmentation uncertainties and

46 46 errors. Despite the overall results of the study, a number of aspects from this study have been introduced into the clinic workflow and have made significant differences in how a patient s RT treatments are planned and followed in our clinic. The UNMC has incorporated this ART technique using CTOR data sets in patients several times during their course of RT treatments. This ART technique offers continual assessment of tumor volume response at specific intervals during RT which allows the physician to adjust the margins on the tumor volumes. The process of utilizing the CTOR data sets to continually adapt RT treatment plans provides the ability to modify the treatment plans to the most current parameters while the tumor volumes are shrinking. With this ART technique, the medical dosimetrists are able to efficiently transfer contours and radiation beams to the CTOR data sets for the physician to review. At that time, the RO is able to determine quickly if they are able to modify the current treatment plan. Sometimes there is no change and the RO will continue with the initial RT plan. If there is a significant change, the RO can very easily modify contours and beams to adapt the patient s RT treatment plan to the most current status. As the tumor volumes reduce in size, the RO has the ability to take the prescription to higher therapeutic doses, as well as reducing the toxicity to the normal tissues. This ART technique that is utilized at UNMC also allows for continual accurate composite treatment plans. It is especially important in thoracic tumors to have accurate composite doses to both the spinal cord and normal lung tissue. If this technique is not efficient, accurate, and effective, it becomes a technique that will not be well utilized in a busy academic clinic. The process has been stream-lined quite effectively and utilized regularly for the benefit of the patients and local control of their disease.

47 47 Tables Table 1: Patient Tumor Volumes from TPS and the Percent Change

48 48 Figures Figure 1: Total Tumor Volume Change Over the Course of RT Percent Change Total Tumor Volume Change Over the Course of RT GTV CTV Patients Figure 2: Tumor Volume Changes by Fractionation Intervals Tumor Volume Changes by Fractionation Intervals First fx-10fx 10fx-20fx 20fx-30fx 30 Percent Change GTV CTV GTV CTV GTV CTV GTV CTV GTV CTV Patients

49 49 Figure 3: Normal Tissue Percent Change for Patient 1 Normal Tissue Percent Change for Patient 1 22 fx (44Gy) 20 fx (40Gy) 10 fx (20Gy) % -8.00% -6.00% -4.00% -2.00% 0.00% 2.00% 4.00% 6.00% 8.00% 10.00% 10 fx (20Gy) 20 fx (40Gy) 22 fx (44Gy) 80% -4.67% -8.32% -8.35% 90% -6.31% -4.84% -4.84% 95% -2.76% -2.75% -2.81% 100% 1.14% 8.17% 8.26% Figure 4: Normal Tissue Percent Change for Patient 4 Normal Tissue Percent Change for Patient 4 30 fx (60Gy) 20 fx (40Gy) 10 fx (20Gy) % % -5.00% 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 10 fx (20Gy) 20 fx (40Gy) 30 fx (60Gy) 80% -1.61% % 11.08% 90% -1.83% -9.35% 15.04% 95% -3.54% -7.81% 17.84% 100% -5.09% -2.17% 27.44%

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