An audit of radiation dose of 4D CT in a radiotherapy department

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1 An audit of radiation dose of 4D CT in a radiotherapy department Poster No.: R-0097 Congress: Type: Authors: Keywords: DOI: 2014 CSM Scientific Exhibit T. Hubbard, J. Callahan, J. Cramb, R. Budd, T. Kron; EAST MELBOURNE/AU Radioprotection / Radiation dose, CT, PET-CT, Audit and standards, Physics, Radiotherapy techniques /ranzcr2014/R-0097 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply RANZCR/AIR/ACPSEM's endorsement, sponsorship or recommendation of the third party, information, product or service. RANZCR/AIR/ ACPSEM is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold RANZCR/AIR/ACPSEM harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies,.ppt slideshows,.doc documents and any other multimedia files are not available in the pdf version of presentations. Page 1 of 9

2 Aim Time resolved 4D CT is used at Peter MacCallum Cancer Centre since July 2007 for radiotherapy treatment planning using a Philips Brilliance Wide Bore CT scanner. It was the aim of this study to review the dose delivered to patients in these procedures and compare it to conventional CTs acquired for treatment planning. Methods and materials 4DCT has been used at Peter MacCallum Cancer Centre since July 2007 for radiotherapy treatment planning using a Philips Brilliance Wide Bore CT scanner (16 slice, helical 4DCT acquisition). All scans are performed at 140kVp and reconstructed in 10 datasets for different phases of the breathing cycle. Dose records were analysed retrospectively for 387 patients who underwent 4DCT procedures between 2007 and Table 1 gives a breakdown of treatment scenarios. CTDIs were evaluated as volume CTDI (CTDIvol) calculated as 2/3 of peripheral dose and 1/3 of the central dose in a standard Perspex phantom. The CTDI values given by the scanner were verified using two in-house built cylindrical Perspex phantoms of 32 and 16cm diameter and a Farmer type ionisation chamber with a Air KERMA calibration factor traceable to the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Dose Length Product (DLP) was calculated from CTDI and scan length. The CTDIs recorded in 4DCT scans were compared with two control groups: 1. A cohort of 25 lung cancer patients who had a 3D CT scan on the same CT scanner during the time period of the study. These could occur if the patient had a previous positron emission tomography (PET) scan which provided sufficient information on tumour motion to inform treatment planning. 2. A cohort of patients having 4DCT scans as part of their time resolved 4D positron emission tomography (PET) scan (GE Discovery 690, 64 slice, 120kV, fixed 10mA). These patients have a 4DCT scan as part of the PET/CT acquisition for attenuation correction and anatomic correlation. Images for this section: Page 2 of 9

3 Table 1: Table 1: Summary of 4D CTs. Some patients can have more than one 4D CT with the total number of patients being 387. Page 3 of 9

4 Results A total of 444 4D CT scans were acquired with the majority of them (342) being for lung cancer radiotherapy. CTDI Vol as recorded over this period was fairly constant at approximately 20 mgy for adults. An overview of the data is shown in figure 1. The CTDI for 4DCT for radiotherapy treatment planning of lung cancers of /- 9.3mGy (n = 168, mean +/- 1SD) is about 50% higher than CTDIs for conventional CT scans that were acquired in the same period with a CTDIVol 12 +/- 4mGy (sample of n = 25). The three paediatric patients scanned in this period with 4D CT had an average CTDI of /- 2 mgy being about 40% lower than the corresponding adult scans. Not surprisingly, CTDI and DLP increased with increasing field of view as shown in figure 2; however, no significant difference between DLPs for different indications (breast, kidney, liver and lung) could be found. Breathing parameters such as breathing rate (range 7 to 29 breaths per minute) did not affect dose as can be seen in figure 3; nor did the shape of the breathing pattern with helical 4D-CT. Similarly, the use of different surrogate markers for breathing motion (Philips bellows or Varian RPM infrared marker) did not make a difference in dose values (data not shown). The data was also compared to 4D CT scans acquired for 4D PET. The CTDIvol in these scans that are used for attenuation correction and anatomic correlation was 6.4 +/- 2.2 mgy (n=25). Images for this section: Page 4 of 9

5 Fig. 3: Figure 3: Variation of CTDIvol with breathing period of all lung cancer patients (n=295). Shown is the regression line for all data (r2 = 0.004). Page 5 of 9

6 Fig. 1: Figure 1: CTDIvol and DLP for 4DCT applications at Peter MacCallum Cancer Centre between 2007 and In order to use the same scale DLP was divided by 50cm before plotting. A scan length of 50cm would yield the same numerical value for CTDI and DLP in the figure. Page 6 of 9

7 Fig. 2: Figure 2: Volume CTDI as a function of the field of view for 4DCTs in the present study. The study set of 4DCT for radiotherapy is compared with 25 3DCTs for lung cancer in the same period and a set of 4DCTs acquired for PET imaging in 25 lung cancer patients. Page 7 of 9

8 Conclusion 4D CT scans can be acquired for radiotherapy treatment planning with a dose less than twice that required for conventional CT scanning. It is also feasible to acquire a low dose 4D-CT scan for use in attenuation correction of 4D-PET images that is approximately half that of a conventional CT scan component within regions affected by shielding from the primary collimator, particularly for smaller fields. Personal information References 1. Keall P: Locating and targeting moving tumors with radiation beams. Front Radiat Ther Oncol 43:118-31, Rietzel E, Rosenthal SJ, Gierga DP, et al: Moving targets: detection and tracking of internal organ motion for treatment planning and patient set-up. Radiother Oncol 73 Suppl 2:S68-72, Keall PJ, Mageras GS, Balter JM, et al: The management of respiratory motion in radiation oncology report of AAPM Task Group 76. Med Phys 33: , Bedi C, Kron T, Willis D, et al: Comparison of radiotherapy treatment plans for left-sided breast cancer patients based on three- and four-dimensional computed tomography imaging. Clin Oncol (R Coll Radiol) 23:601-7, Siva S, Chesson B, Aarons Y, et al: Implementation of a lung radiosurgery program: technical considerations and quality assurance in an Australian institution. J Med Imaging Radiat Oncol 56:354-61, Callahan J, Binns D, Dunn L, et al: Motion effects on SUV and lesion volume in 3D and 4D PET scanning. Australas Phys Eng Sci Med 34:489-95, Clements N, Kron T, Franich R, et al: The effect of irregular breathing patterns on internal target volumes in four-dimensional CT and cone-beam CT images in the context of stereotactic lung radiotherapy. Med Phys 40:021904, Callahan J, Kron T, Schneider-Kolsky M, et al: Validation of a 4D-PET maximum intensity projection for delineation of an internal target volume. Int J Radiat Oncol Biol Phys 86:749-54, 2013 Page 8 of 9

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