SU‐E‐T‐766: Verification of Volumetric Modulated Arc Therapy Plans with Independent Three Dimensional Dose Computation Algorithm

Purpose: To verify the volumetric modulated arc therapy (Rapidarc) plans using a independent three dimensional dose computation algorithm using COMPASS system. Methods: Rapidarc is a treatment technique which produces conformal dose distribution by delivering the dose in a rotational fashion while simultaneously changing MLC position, dose rate as well as gantry speed. COMPASS dosimetry system uses the Collapsed Cone Convolution(CCC) algorithm as a dose calculation engine which requires machine model information and beam modeling to display the 3D dose distribution on a patient CT data. Treatment plans (10 patients) generated for Rapidarc on Eclipse (version 8.9) Treatment Planning System (TPS) using Analytical Anisotropic Algorithm (AAA) were exported as DICOM file to COMPASS for recalculation using CCC algorithm. Pilot studies were performed for 2DRT, 3DCRT and IMRT plans prior to VMAT plan verification. The doses and dose‐volume histograms computed using CCC were compared with TPS calculated plans. Plans were analyzed in terms of Conformity Index (CI) for PTV, maximum and mean doses for OARs and difference in three dimensional gamma. Results: The average 3D mean gamma for 1mm(DTA) and 1%(DD) criteria for 2DRT and 3DCRT was 0.11 ±0.002 . Maximum and minimum deviation of PTV Volume receiving 95% of the prescribed dose(V95%) for IMRT and Rapidarc were found to be 1.01%, 0.79% and 1.24%, 0.86% respectively. Average deviation of maximum and mean doses of OAR's for IMRT and Rapidarc were 0.91±0.002 %, 0.55±0.008 % and 0.25±0.005 %, 1.05±0.009 % respectively. Conclusions: This study illustrates that the compass three dimensional dosimetry system can be used as an accurate and effective tool to clinically validate the Rapidarc plans independently.