[Study on the Effectiveness of QA/QC Methods for Non-physical Wedges by Comparing EPID and 2D Array Detector Beam Profiles].

Abstract

Purpose: Beam profiles of enhanced dynamic wedge (EDW), a non-physical wedge, were obtained using EPID and 2D array detector, and the effectiveness of the QA/QC method for EDW using EPID was investigated.

Methods: Using a radiotherapy unit (Clinac iX; Varian Medical Systems, Palo Alto, CA, USA), the EDW beam profile was measured 10 times with an EPID (aS1000; Varian Medical Systems) and a 2D array detector (Profiler2; Sun Nuclear, Melbourne, FL, USA) to evaluate the reproducibility of the set-up and the EDW beam profiles. The beam profiles of the physical wedge were also obtained with EPID and Profiler2 as a comparison for the EDW beam profiles. In addition, EDW irradiation logs were obtained to analyze output fluctuations during EDW irradiation.

Results: Comparing the EPID and Profiler2 reproducibility of beam profiles, the EPID showed better setup position reproducibility, but the Profiler2 showed better EDW reproducibility of beam profiles. The coefficient of variation for the physical wedge reproducibility of beam profiles was equal or smaller for EPID, and for the EDW irradiation log, the variation was more significant for larger EDW angles.

Conclusion: The effectiveness of the QA/QC method for EDW by EPID is high because EPID is considered to capture the EDW variation in detail and the installation accuracy is also excellent.