The Effects of DIBH on Liver Dose during Right-Breast Treatments Introduction

Transcription

1 1 The Effects of DIBH on Liver Dose during Right-Breast Treatments Megan E. Sullivan B.S.R.T.(T)., Patrick A. Melby, B.S. Ashley Hunzeker, M.S., CMD, Nishele Lenards, M.S., CMD Medical Dosimetry Program at the University of Wisconsin - La Crosse, WI Introduction Radiation therapy has been used for breast cancer for over 40 years. The results have shown to be very beneficial in terms of cancer treatment, along with the total survival rate. During these treatments, cancer tissues were irradiated including normal tissue within the treatment field. With increasing technology, techniques have been developed to increase the accuracy of treatments, while reducing the exposure to surrounding areas. A relatively new technique includes the use of a four-dimensional computed tomography (4DCT), using a protocol called deep inspiration breath hold (DIBH). The DIBH technique is one method of treatment using a gated scan. Gated scans consist of taking CT images while the patient is at a specific time of their breathing cycle. This creates a consistent time to conduct a treatment that has far less motion compared to treating without it. Without a method of gating, the chest can fluctuate 0.5 to 0.7cm laterally throughout the treatment. 1 During DIBH treatments, the gate at which the CT scan is acquired is set to when the patient is at full inspiration. Deep inspiration breath hold treatments have other benefits. The lung volume is increased during DIBH procedures. With this increase, the electron density within the lung is decreased, reducing the exposure to the lung while increasing the distance between the treatment fields from organs at risk (OR) within the area. 2 Because the heart is located slightly to the left side of the body, the extra separation that DIBH creates helps reduce unnecessary exposure to the coronary arteries. This is why DIBH are mainly used for left-sided breast cancer treatments. Right-sided DIBH treatments are less common. Other gating techniques such a free breathing (FB) or no gating at all are used for right-sided treatments. The reason for this is that DIBH can be difficult to set-up and execute if the patient has a difficult time holding their breath. Due to the location of the heart, it is of less concern in right-sided breast cancer treatments, but DIBH will relocate other organs, specifically the liver, away from the radiation

2 2 field. One study showed that during normal respiration, the liver and diaphragm moved 0.7 to 2.8cm., 1 and during DIBH the distance is further increased. This motion may significantly reduce additional radiation being deposited into the liver. The purpose of this study is to determine if DIBH would decrease the amount of radiation to the liver for right sided breast cancer patients. Case Description Selection X amount of previously treated patients with breast cancer to the right-breast and regional lymph nodes were selected. All of these patients received radiation therapy with the DIBH technique to minimize lung dose. In CT simulation, patients were scanned with both FB and DIBH scan. s were positioned supine on an in-house, inclined breast board with both arms raised and heads turned towards the unaffected breast. Radio-opaque marker wires were placed by the physician to delineate superior, inferior, medial, and lateral field borders as well as breast tissue and lumpectomy scars. A Philips Brilliance Big Bore CT scanner was used to acquire the FB and DIBH scans with a 3.0 mm slice thickness. The FB scan was acquired first. For the DIBH scans, the patients were gated with Real-time Position Management (RPM) system and were coached with breathing instructions. Before the DIBH scan began, the patients were expected to reproduce a consistent breath hold in order to ensure reproducibility for treatment. The expected time for patients to hold their breath for this scan was about 20 seconds. Upon acquisition of the scans, the CT data sets were transferred to the Eclipse Treatment Planning System (TPS) via Digital Imaging and Communications in Medicine (DICOM) network. Target Delineation Target volumes including the breast tissue, lumpectomy bed, axillary I, II, and III lymph nodes, supraclavicular lymph nodes, and in some cases, intramammary (IM) nodes were contoured by the physician and outlined on both the FB and DIBH scans. The breast tissue was cropped 5 mm away from the surface. Organs at risk were defined by certified medical dosimetrist and included the following: right and left lungs, heart, spinal cord, esophagus, and liver.

3 3 Treatment Planning The prescription was written for 50.4 Gy in 1.8 Gy per fraction to be delivered daily. The planning goals for the target volumes were to achieve at least 95% of the volume to be covered by at least 95% of the prescribed dose. In cases involving the internal mammary (IM) nodes, the goal was to achieve 90% of the volume to be covered with 90% of the prescribed dose. A monoisocentric technique was used for all patients. Three different linear accelerators were available to treat DIBH breast plans including two Varian Truebeams which offered energies of 6, 10, and 15 MV and a Varian 21EX which offered 6 and 23 MV energies. Treatment angles and multi-leaf collimator (MLC) blocks for the supraclavicular fields were created based on obtaining coverage of the nodal chains and the need to block the spinal cord, esophagus, and humeral head. Treatment angles and MLC blocks for tangent fields were created based on the field borders defined in CT simulation and the ability to block normal structures such as heart and liver without compromising coverage of the breast tissue. When helpful, a field in field technique was used to block out unnecessary hot spots. An example of treatment angles and beam energies for two patients can be found in Table 1. The plans used to treat the patients were created on the DIBH scans by certified medical dosimetrists. Plan Comparisons For the actual treatments, plans were generated on the DIBH scans by certified medical dosimetrists. For research purposes, retrospective planning was done on the FB scans and compared against the plans created on the DIBH scans to assess the dose to the liver for each patient. This was accomplished by copying the DIBH plan onto the FB scan. Adjustments were made as necessary in order to generate a plan tailored to the FB scan while simultaneously keeping the plan as similar to the DIBH plan as possible. To evaluate a fair comparison, plans were normalized appropriately in order to obtain the same target coverage and the dose volume histograms (DVH) were evaluated. All planning goals remained consistent for each patient regardless of the structure set.

4 4 Results The liver metric doses compared from the FB plan to the DIBH plan included the following: Volume within the target in cc, mean and maximum dose in Gy, V30, V20, V10, and V5 in cc. The results can be found in Table 2. Discussion The results of the current study demonstrates that DIBH techniques can show a reduction in the amount of radiation received by the liver. The reduction of dose was due to the movement of the liver outside of the treatment fields. To our knowledge, this is one of the first studies that has taken an in-depth look at liver dose using DIBH techniques for multiple patients. A previous study did look at a single case study and calculated the dose received by the liver for both the DIBH and FB. The results were similar. They had found for this single case that DIBH reduce the mean and max dose by 46 and 3.5% respectively. 3 The V10, V20, and V30 were all decreased by over 50% to show an overall benefit to DIBH. The liver scanned in our studies was shown to have moved between and??? to???cm further inferior during DIBH when compared to FB. This helps to keep the liver out of the treatment fields. The volume of liver treated in the FB scans was between 2.3 cc and 85.7 cc whereas the DIBH technique was able to minimize the volume of the liver within the target field to between 0 cc and 12.4 cc. This volume reduction led to a decrease in every other liver metric measured for this study, namely a decrease in the mean dose and integral dose. In cases where the liver was completely removed from the field, the dose going to the liver would only be from scattered irradiation. The suggested dose tolerances for the liver is a mean dose of less than 30Gy which gives a 5% chance of radiation induced liver disease (RILD). 4 One case of RILD has been documented to be caused by a treatment of the right chest wall. 5 It was found during a followup CT scan in which physicians found a straight edge of abnormal attenuation within the liver. The location of this abnormality was in the direct path of the radiation beam from a previous treatment to the right chest wall and the abnormality was determined to be RILD. Radiation induced liver disease may progress to liver fibrosis and liver failure. So although the mean dose of 30 Gy is relatively high compared to the mean doses we

5 5 have discover for both FB and DIBH scans, documented cases of RILD have been found in the past. Preexisting liver disease such as hepatitis or poor liver function may have a greater risk of side effects. 3 This could be of greater concern, because liver disease is becoming an increasingly prevalent disease. It is estimated that 1 in 3 adults and 1 in 10 children in America have nonalcoholic fatty liver disease (NAFLD). 6 It has increased significantly based off of the increase in obesity, type II diabetes mellitus, and physical inactivity. The excess fat within the liver may cause hepatitis, which may then form scar tissue within the liver, causing a decrease in liver function. With a greater possibility for future patients to have decreased liver function, it is of best practice to spare this organ from unnecessary radiation during right-breast treatments Another reason to reduce the excess radiation dose to the liver is because patients are being treated at a younger age. The advances in screening have allowed for patients to catch and treat breast cancer early. Since patients are being treated at a younger age, they would have more time to develop a secondary cancer in any areas that received a low dose of radiation. By using DIBH it decreases radiation dose to the liver, decreasing the risk for a secondary cancer within the liver. The functionality of the liver is continuing to decrease with our current behavioral practices. This along with decreasing the risk of secondary cancers to the liver are reasons why it is important to try to spare excess dose from being deposited into the liver from right-sided breast treatments. Conclusion

6 6 References 1. Butler LE, Forster KM, Stevens CW, et al. Dosimetric benefits of respiratory gating: a preliminary study. J Appl Clin Med Phys. 2004;5(1): Bruzzaniti V, Abate A, Pinnarò P, et al. Dosimetric and clinical advantages of deep inspiration breath-hold (DIBH) during radiotherapy of breast cancer. J Exp Clin Cancer Res. 2013;32(1): Rice L, Harris S, Green M, Price P. Deep inspiration breath-hold (DIBH) technique applied in right breast radiotherapy to minimize liver radiation. BJR case reports. 2015;1(2): Emami B, Lyman J, Brown A, et al. Tolerance of normal tissue to therapeutic irradiation. Int J Rad Oncol Biol Phys. 1991;21(1): y 5. Khozouz R, Huq S, Perry M. Radiation-Induced Liver Disease. J Clin Oncol. 2008;26(29): López-Velázquez JA, Silva-Vidal KV, Ponciano-Rodríguez G, et al. The prevalence of nonalcoholic fatty liver disease in the Americas. Ann Hepatol. 2014;13(2): Published January 18, Accessed July 23, 2016

7 7 Figures Figure 1. Image registration of FB and BH scans on patient 1 in the coronal plane with treatment fields displayed.

8 8 Figure 2. Image registration of FB and BH scans on patient 1 in the sagittal plane with treatment fields displayed.

9 9 Figure 3. Beams eye view of medial tangent field on FB scan (left) and BH scan (right) for patient 6. Breast contour is shown in green and liver contour is shown in brown. FB BH Figure 4. Dose volume histogram in absolute dose and absolute volume for patient 6. Breast coverage is shown in green and liver coverage shown in brown.

10 10 FB BH Figure 5. Dose volume histogram in absolute dose and absolute volume for patient 6 showing a zoomed in comparison of the liver dose for each plan.

11 11 Table 1. Field data for patient 6 and patient Energy (MV) Gantry (Degrees) Collimator (Degrees) Tables Fld 1 Fld 2 Fld 3 Fld 4 Fld 5 Fld 6 Fld 7 LAO LAO RPO LAO LAO RPO RPO SCLAV SCLAV SCLAV BREAST BREAST BREAST BREAST Wedge Fld 1 Fld 2 Fld 3 Fld 4 Fld 5 Fld 6 Fld 7 Fld 8 LAO RPO LAO LAO LAO FIF RPO RPO RPO FIF SCLAV SCLAV BREAST BREAST BREAST BREAST BREAST BREAST Energy (MV) Gantry (Degrees) Collimator (Degrees) Wedge EDW10 OUT W30R W30R W30R Table 2. The liver doses comparing FB and DIBH techniques Volume within target field (cc) Mean dose (Gy) FB Max dose (Gy) V30 (cc) V20 (cc) V10 (cc) V5 (cc) DIBH Volume within target field (cc) Mean dose (Gy) Max dose (Gy) V30 (cc) V20 (cc) V10 (cc) V5 (cc)

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