SU‐E‐T‐191: Transit Dose Based Quality Assurance of Intensity Modulated Radiotherapy with Two Dimensional Array Detector

Abstract

Purpose: The purpose of this work is to evaluate the possibility of the transit dose based verification of the accuracy in dose delivery to the patient with two dimensional array dosimeter. Methods: Five intensity modulated radiotherapy (IMRT) plans were selected from lung cancer patients and irradiated on a homogeneous solid water phantom and an inhomogeneous anthropomorphic phantom. To simulate error in patient positioning, the anthropomorphic phantom was displaced from 5 mm to 10 mm in the superior to inferior (SI), inferior to superior (IS), right to left (RL), and left to right (LR) directions. The transit dose distribution was measured with MAPCHECK2 and was compared to the computed dose map based on gamma index analysis. Results: While the average passing rate based on gamma index with a 3% dose and a 3 mm distance‐to‐dose agreement tolerance limit was 98.6 % for the transit dose with homogeneous phantom, it was reduced to 95.5 % for the transit dose with inhomogeneous anthropomorphic phantom. The transit dose analysis shows that the average passing rate decreases up to 11.5% and 16.6% in gamma index for 5 mm and 10 mm setup error, respectively. Conclusion: Our feasibility study suggests that the transit dose based quality assurance can provide the information about the accuracy of the inhomogeneity correction algorithm and patient positioning during treatment, which can be used to verify the accuracy in actual dose delivery to the patient in treatment room.