International Journal of Cancer Therapy and Oncology www.ijcto.org Corresponding author: Birendra Kumar Rout; Department of Radiation Physics, Indo-American Cancer Institute and Research Center, Hyderabad, India. Cite this article as: Rout BK, Shekar MC, Kumar A, Muralidhar KR. Dosimetric Study of RapidArc plans and conventional intensity modulated radiotherapy for prostate cancer involving seminal vesicles and pelvis lymph nodes. Int J Cancer Ther Oncol 2016; 4(1):418. DOI: 10.14319/ijcto.41.8 © Rout et al. ISSN 2330-4049 Dosimetric study of RapidArc plans and conventional intensity modulated radiotherapy for prostate cancer involving seminal vesicles and pelvis lymph nodes Birendra Kumar Rout 1,2 , Mukka Chandra Shekar 2 , Alok Kumar 3 , Kanaparthy Raja Muralidhar 4 1 Department of Radiation Physics, Indo-American Cancer Institute and Research Center, Hyderabad, India 2 Department of Physics, Jawaharlal Nehru Technological University, Hyderabad, India 3 Department of Radiation Physics, Mahavir Cancer Sansthan, Patna, India 4 Department of Radiation Physics, American Oncology Institute, Hyderabad, India Received September 23, 2015; Revised January 12, 2016; Accepted January 17, 2016; Published Online January 24, 2016 Original Article Abstract Purpose: The main purpose of this study is to (1) identify the continual diversity between conventional fixed field intensity modulation radiotherapy (IMRT) and RapidArc (RA) for high-risk prostate cancer; and (2) determine potential benefits and drawbacks of using for this type of treatment. Methods: A cohort of 20 prostate cases including prostate, seminal vesicles and pelvic lymph nodes was selected for this study. The primary planning target volume (PTVP) and boost planning target volume (PTVB) were contoured. The total prescription dose was 75.6 Gy (45 Gy to PTVP and an additional 21.6 Gy to PTVB). Two plans were generated for each PTV: multiple 7-fields for IMRT and two arcs for RA. Results: A Sigma index (IMRT: 2.75 ± 0.581; RA: 2.8 ± 0.738) for PTVP and (IMRT: 2.0 ± 0.484; RA: 2.1 ± 0.464) for PTVB indicated similar dose homogeneity inside the PTV. Conformity index (IMRT: 0.96 ± 0.047; RA: 0.95 ± 0.059) for PTVP and (IMRT: 0.97 ± 0.015; RA: 0.96 ± 0.014) for PTVB was comparable for both the techniques. IMRT offered lower mean dose to organ at risks (OARs) compared to RA plans. Normal tissue integral dose in IMRT plan resulted 0.87% lower than RA plans. All the plans displayed significant increase (2.50 times for PTVP and 1.72 for PTBB) in the average number of necessary monitor units (MUs) with IMRT beam. Treatment delivery time of RA was 2 ‒ 6 minutes shorter than IMRT treatment. Conclusion: For PTV including pelvic lymph nodes, seminal vesicles and prostate, IMRT offered a greater degree of OARs sparing. For PTV including seminal vesicles and prostate, RA with two arcs provided comparable plan with IMRT. RA also improved the treatment efficiency due to smaller number of MUs required. Keywords: IMRT, RapidArc, Sigma-Index, Conformity Index, Normal Tissue Integral Dose 1. Introduction Cancer is the major cause of leading deaths in the 21 st century in world with 14.1 million cases and 8.2 million deaths in 2012. 1 Among them, prostate cancer stands as important due to risk of secondary malignancies associated with intensity modulation radiation therapy (IMRT) with conventional 3-dimentional conformal radiotherapy (3D-CRT). 2 Among the different technologies adopted to cure the prostate cancer, external radiotherapy is recognized as one of the important treatment options. 3-4 The technology aims to destroy cancer cells by minimal damaging (due to risk of secondary malignancies) to the surrounding normal tissues. It creates the best possible balance between maximizing dose to prostate cancer cells and minimization of side effects. IMRT technology for prostate tumor/cancer allows less toxicity in comparison to 3D-CRT. 5 The development of IMRT technique has enabled the delivery of highly conformal