Portal Dosimetry for Pre-treatment Verification of Imrt/Vmat Plan: A Comparison with 2D Array Detector for Quality Assurance

Abstract

Purpose: The present study is to investigate the measured and calculated doses for different malignant tumours utilizing various gamma criteria and QA for confirmation of IMRT/VMAT with portal dosimetry and 2D array. Methods: Different malignant tumors are treated by IMRT/VMAT techniques on Varian IX linear accelerator with 6 MV photon beams. Treatment planning system (TPS) is used to plan Patient’s charts. Gamma Index (GI) variation is compared to the procedure of pre-treatment verification in IMRT/VMAT plans. Results: The gamma criteria (DD/ DTA) of IMRT for (3%/3 mm), mean ± SD are γ≤ 1%=99.41% ± 0.67%, γmax=2.11 ± 0.56 and γavg=0.23 ± 0.03 by EPID, and γ% ≤ 1=98.55% ± 0.79%, γmax=1.65 ± 0.45 and γavg=0.27 ± 0.04 by using 2D array. For VMAT mean ± SD are γ% ≤ 1= 99.42% ± 0.67%, γmax=2.11 ± 0.56 and γavg= 0.19 ± 0.05 using portal dosimetry, and γ% ≤ 1=99.36% ± 0.53%, γmax=1.65 ± 0.45 and γavg=0.22 ± 0.05 using 2D array. Conclusions: Specific QA of IMRT/VMAT patient using (portal dosimetry or 2D array) to verify IMRT/VMAT fields. 3%/3 mm is the most appropriate of gamma criteria (DD/DTA) for IMRT/VMAT plans quality assurance. The control chart is an effective tool to detect uncontrolled variation.