VMAT plans for treatment prostate cancer: Dosimetric verifications and comparison with 3D-CRT and IMRT

VMAT plans for treatment prostate cancer: Dosimetric verifications and comparison with 3D-CRT and IMRT Poster No.: C-0520 Congress: ECR 2011 Type: Scientific Exhibit Authors: Y. Kawasaki, S. Tadokoro, Y. Nemoto, J. Shirai, S. Nakano, 1 1 1 2 1 2 1 1 1 2 N. Eguchi, S. Izumi, T. Nose ; Ibaraki/JP, Tokyo/JP Keywords: Oncology, Physics in radiology, Pelvis, CT, Radiation therapy / Oncology, Dosimetry, Physics, Biological effects DOI: 10.1594/ecr2011/C-0520 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 ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR 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 ECR 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 and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 22

Purpose Volumetric modulated arc therapy (VMAT) is a completely dynamic technique using one or more gantry arcs. Treating with many arcs may ensure high dose conformity and normal tissue sparing, and also reduce the number of MU and delivery times than other established modulating techniques. However, because of the novel and dynamic operating system of the Linac, VMAT plans require accurate dosimetric verifications. As a first step, we compared 3D-CRT and step-and-shoot IMRT plans with VMAT plans for prostate cancer with respect to DVH indexes for target and OARs, total MU, and total delivery times. As a second step, VMAT plans were verified using two independent dosimetric systems. Images for this section: Page 2 of 22

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Methods and Materials 3D-CRT, step-and-shoot IMRT plans, single-arc and two-arcs VMAT plans (Pinnacle3 Ver.9 PHILIPS) for 15 prostate cancer patients were created for an ELEKTA Synergy linear accelerator with 1cm leaf MLC (Table 1). A total of 15 3D-CRT plans, 15 step-and-shoot IMRT plans, 15 single arc, VMAT plans (VMAT 1), and 15 double arc, VMAT plans (VMAT 2). Dose prescription was 72 Gy in 36 fractions. Uniform OAR dose constraints were used for 3D-CRT and IMRT and VMAT plans. All plans were then evaluated in terms of numbers of MUs, treatment delivery times, D95 of the PTV, rectum V60 Gy, bladder V60 Gy, femoral max dose. Absolute point doses were using a water-filled cylindrical phantom at isocenter position. Calculated and measured 2D dose distributions were compared using gafchromic EBT2 films in a dedicated solid water phantom and gamma index analysis. All plans were also delivered to the ArcCheck phantom and the data measured by the 2 diode arrays compared with the planned 3D dose distributions by means of ArcCHECK dedicated software. Images for this section: Page 4 of 22

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Results Mean MUs and treatment times for 3D-CRT (329.9MU, 215.9 s), VMT1 (354.9MU, 121.3 s) and VMAT2 (399.4MU, 226.7 s) were significantly lower (p<0.05) than that for IMRT values (480.3MU, 432.5 s) (Table 2). Mean D95 values for 3D-CRT, IMRT, VMAT1 and VMAT2 were 70.1Gy, 72.1 Gy, 72.0 Gy and 72.0 Gy (Fig. 1-3). Mean values for rectum V60 Gy were 29.3% (3D-CRT), 18.8% (IMRT), 18.7% (VMAT1), and 18.7% (VMAT2). Mean values for bladder V60 Gy were 3.9% (3D-CRT), 4.6% (IMRT), 4.8% (VMAT1), and 4.8% (VMAT2). Mean values for femoral max doses were 53.9 Gy (3D-CRT), 41.0 Gy (IMRT), 39.6 Gy (VMAT1), and 39.7Gy (VMAT2). Point dose values measured using ion chamber at the isocenter for all plans were all within 3% of the corresponding calculated values (Table 3). Comparison between calculated and measured planar dose distributions yielded an average pass rate using gamma index (3mm, 3%) of 92.5% (3D-CRT), 90.6% (IMRT), 91.7% (VMAT1), and 91.5% (VMAT2) for EBT2 (Table 4). As for the evaluation by ArcCHECK, similar results to that obtained with gafchromic EBT2 films were observed, but with significantly higher pass rate of the gamma index (p<0.05) (Fig. 3,4). Images for this section: Page 7 of 22

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Conclusion Our results for plan comparison displayed VMAT can significantly reduce MUs and treatment times compared to step and shoot IMRT while keeping the same level of DVH indexes for target and OARs. Both dosimetric verifications using gafchromic EBT2 films and ArcCHECK showed VMAT plans were reproducible enough to be used in daily practice. We were convinced that it was safe, effective technology. Images for this section: Fig. 1 Page 16 of 22

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References [References] 1) Men C, Romeijn HE, Jia X, Jiang SB. "Ultrafast treatment plan optimization for volumetric modulated arc therapy (VMAT)", Med Phys. 2010 Nov;37(11):5787-91. 2) Dobler B, Weidner K, Koelbl O. "Application of volumetric modulated arc therapy (VMAT) in a dual-vendor environment", Radiat Oncol. 2010 Oct 25;5:95. 3) Hardcastle N, Tomé WA, Foo K, Miller A, Carolan M, Metcalfe P. "Comparison of prostate imrt and vmat biologically optimised treatment plans", Med Dosim. 2010 Aug 26. 4) Bedford JL. "Treatment planning for volumetric modulated arc therapy",med Phys. 2009 Nov;36(11):5128-38. 5) Haga A, Nakagawa K, Shiraishi K, Itoh S, Terahara A, Yamashita H, Ohtomo K, Saegusa S, Imae T, Yoda K, Pellegrini R. "Quality assurance of volumetric modulated arc therapy using Elekta Synergy", Acta Oncol. 2009;48(8):1193-7. 6) Zhang P, Happersett L, Hunt M, Jackson A, Zelefsky M, Mageras G. "Volumetric modulated arc therapy: planning and evaluation for prostate cancer cases", Int J Radiat Oncol Biol Phys. 2010 Apr;76(5):1456-62. Epub 2009 Jun 18. 7) Bedford JL, Warrington AP. "Commissioning of volumetric modulated arc therapy (VMAT)", Int J Radiat Oncol Biol Phys. 2009 Feb 1;73(2):537-45. 8) Palma D, Vollans E, James K, Nakano S, Moiseenko V, Shaffer R, McKenzie M, Morris J, Otto K. "Volumetric modulated arc therapy for delivery of prostate radiotherapy: comparison with intensity-modulated radiotherapy and three-dimensional conformal radiotherapy", Int J Radiat Oncol Biol Phys. 2008 Nov 15;72(4):996-1001. Epub 2008 May 1. Images for this section: Page 18 of 22

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Personal Information Y. Kawasaki Department of Medical Physics for Radiotherapy, Hitachi, Ltd, Hitachinaka General Hospital 20-1, Ishikawa-cyo, Hitachinaka-shi, Ibaraki, 312-0057,Japan mail to : yoshiyuki.kawasaki.ma@hitachi.com S. Tadokoro, Y. Nemoto, J. Shirai, S. Nakano Department of Radiological Technology, Hitachi, Ltd, Hitachinaka General Hospital H. Imura, T. Suzuki Department of Radiological Technology, Hitachi, Ltd, Hitachi General Hospital N. Eguchi Department of Radiology, Hitachi, Ltd, Hitachinaka General Hospital S. Izumi Department of Radiation Oncology, Tokyo Women's Medical University T. Nose Department of Radiation Oncology, Nippon Medical School Tamanagayama Hospital Images for this section: Page 20 of 22

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