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Determination of IMRT Factor for VMAT Treatment Technique

Amanjot Kaur1,2*, P. N. Pawaskar2 , G. Sahani3 , (1) Mahatma Phule Charitable Trust Hospital, Navi Mumbai, India, (2) D. Y. Patil Education Society (Deemed to be University), Kolhapur, India, (3) Atomic Energy Regulatory Board, Mumbai, India


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To find out IMRT Factor [C1] for Volumetric Modulated Arc Therapy (VMAT) treatment technique to estimate contribution of VMAT treatment technique in leakage workload of an advanced medical linear accelerator vault.

Methods: For the given prescribed doses, VMAT and conventional treatment plans of various cases such as head and neck, esophagus, cervix, brain etc. were created using Varian’s Eclipse Treatment Planning System (TPS) with 6 MV x-ray photon beam energy. The total monitor units obtained for VMAT and conventional treatment plans for each case were used to find out IMRT factor using formula, as defined in NCRP report no. 151, i.e. IMRT Factor [C1] = MU[IMRT] / MU[CONV].

Results: The IMRT factors for VMAT treatment technique calculated using treatment plans for variety of treatment sites are found to be varying in range 1.2 – 3.2. The average IMRT factor for VMAT is found to be 2.

Conclusion: As IMRT factor for VMAT treatment dose delivery technique is found to be 2, therefore, radiation shielding requirement of secondary barrier will be higher as compared to conventional treatment technique. Based on the already published data in the literature on IMRT factor, its value for IMRT treatment technique is reported to be between 2 to 10 or even more in certain cases. Hence, it can be concluded that leakage workload for secondary barrier of a radiotherapy bunker designed for IMRT cases is higher and hence safer for VMAT treatment technique. Further, if the radiotherapy centre is planning to install medical linear accelerator with expected majority of cases to be treated with VMAT treatment technique and especially treatment cases with newly introduced Halcyon machine, then radiation shielding requirement for secondary barrier can be further optimized accordingly for given shielding design goal using above reported IMRT factor for VMAT treatment technique in this study.


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