SU‐E‐P‐35: Real‐Time Patient Transit Dose Verification of Volumetric Modulated Arc Radiotherapy by a 2D Ionization Chamber Array

Abstract

Purpose:To explore the real‐time dose verification method in volumetric modulated arc radiotherapy (VMAT) with a 2D array ion chamber array.Methods:The 2D ion chamber array was fixed on the panel of electronic portal imaging device (EPID). Source‐detector distance (SDD)was 140cm. 8mm RW3 solid water was added to the detector panel to achieve maximum readings.The patient plans for esophageal, prostate and liver cancers were selected to deliver on the cylindrical Cheese phantom 5 times in order to validate the reproducibility of doses. Real‐time patient transit dose measurements were performed at each fraction. Dose distributions wereevaluated using gamma index criteria of 3mm DTA and 3% dose difference referred to the firsttime Result.Results:The gamma index pass rate in the Cheese phantom were about 98%; The gamma index pass rate for esophageal, liver and prostate cancer patient were about 92%,94%, and 92%, respectively; Gamma pass rate for all single fraction were more than 90%.Conclusion:The 2D array is capable of monitoring the real time transit doses during VMAT delivery. It is helpful to improve the treatment accuracy.