SU-FF-T-235: Patient-Specific QA of Intensity-Modulated Arc Therapy with 2D Diode Array: Initial Experience

Abstract

Purpose: New rotational intensity‐modulated radiation therapy(IMRT) or intensity‐modulated arc therapy (IMAT) techniques using single or multiple arcs are attaining widespread adoption in clinic due to their superior delivery efficiency. This study evaluates the use of a 2D diode array for patient‐specific QA for such techniques with the Varian RapidArc™. Method and Materials: A RapidArc plan conforming to the clinical standards was generated for each case using Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA). A verification plan was subsequently created for each of the treatment plans with the water‐equivalent MapPHAN™ QA phantom, with the MapCHECK™ (Sun Nuclear Corporations, Melbourne, FL) embedded at 5 cm depth, measuring the coronal dose plane in integration mode. Twenty‐one cases were selected in this study including 2 brain, 11 head‐and‐neck (HN), 4 prostate, and 4 whole pelvis cases. The measured 2D dose distributions were then compared to that calculated by Eclipse using (i) gamma analysis with the acceptance criteria of 3%/3mm, and (ii) absolute point dose difference. Results: For all cases, the average passing rate for the gamma analysis was 98.2% (range: 95.3% – 100%) and the absolute point dose difference was 2.1% (range: 0%–3.9%). The total time taken for the QA process was approximately 10 – 15 minutes, including setup, plan delivery, and online analysis. Conclusions: Preliminary results have shown that a 2D diode array is an efficient method for RapidArc patient‐specific QA, proving that the MapCHECK/MapPHAN is capable of performing both absolute and relative dose comparisons with a satisfactory accuracy for clinical practices. Research sponsored by Varian Medical Systems.