SU‐E‐T‐179: Quality Assurance of Enhanced Dynamic Wedge Profiles Using I''mRT MatriXX

Purpose: To evaluate the performance of the I'mRT MatriXX for periodical quality assurance (QA) of enhanced dynamic wedge (EDW) profile. To verify the treatment planning system (TPS) EDW models. Methods: The ionization chamber based MatriXX (IBA, Schwarzenbruck, Germany) was used to measure the EDW profiles of the Varian 21EX Linac with various wedge angles (15, 30, 45, and 60 degrees) and field sizes. The source to detector distance was 100 cm and 4 or 5 cm of buildup was used for 6 or 18 MV respectively. Planar dose fluences were generated by TPS (Philips Pinnacle version 9.0), then we compared the calculated TPS data to the data measured with MatriXX using the OmniPro‐I'mRT software. Profiles were then extracted and exported to a spreadsheet for point‐to‐point comparisons between the TPS calculated and the measurements. We also measured selected profiles using a 0.6 cc ionization chamber in solid slab phantom. Results: Point‐to‐point differences between planned and measured EDW profiles for wedge angles of 15°, 30°, 45°, and 60° in both Y1‐in and Y2‐out directions were analyzed for field sizes of 5×5, 10×10 and 20×20 cm̂2 on three Varian Linacs. For 10×10 cm̂2 field, all four wedge angles the point‐to‐point differences within 80% of the field width were less than 2% for both 6 MV and 18 MV beams. Agreements were not as good for smaller field sizes. Comparisons with a 0.6 cc chamber were only done for the 60° wedge 6 MV beam with field of 20×20 cm̂2, the point‐to‐point comparison both Y1‐in and Y2‐out wedge orientations shows that the ion chamber's results agreed with the MatriXX within 1% in 80% field width. Conclusions: This study demonstrates that MatriXX is a reliable tool and is an efficient approach for both TPS commissioning and periodical QA for EDWs.