SU-E-T-70: A Protocol for Comprehensive Acceptance/Commissioning of Complex 3D QA Devices

Purpose: To develop an acceptance testing and commissioning protocol for a complex pseudo‐3D device (Delta4, Scandidos) before clinical implementation for quality assurance of IMRT/VMAT. Methods: This protocol involves safety, hardware and software functionality, calibration, geometric accuracy, dosimetric accuracy, accuracy of the software interpolation from two 2D diode measurement planes to a 3D dose distribution, end‐to‐end testing, and a comparison to alternative QA methods. Following acceptance testing, 5 commissioning test sets were developed: (1) 4‐field box plans comparing energy‐specific measurements, (2) measurements in multiple device orientations to estimate the accuracy of the software interpolation from 2D diode planes to 3D distribution, (3) detection of known errors, (4) end‐to‐end testing of representative patient plans, and (5) comparison with previous QA devices. Analysis was done based on the gamma index (global 3%, 3mm, 5% threshold) and direct comparison of measured doses. Results: Change in photon energy had no discernible effect. Direct measurements (from the two diode planes) agreed within +/−1% with interpolated measurements (software‐generated 3D distribution). Passing rates were unaffected by device orientation. Plans with known errors failed QA as expected (%voxels passing gamma 99% passing) for prostate, anal cancer, gyn, head‐and‐neck, brain, and stereotactic five‐target brain plans. Increased passing rates were seen compared to prior QA devices (92–98%for a 2D ion chamber array, 0.4–2.9% discrepancies with a 1D ion chamber), perhaps due to the increased number of points evaluated in 3D. Conclusions: A comprehensive ATP and commissioning protocol was developed for a 3D QA device and successfully implemented. It should beapplicable to any clinic. This protocol can be used as a baseline for quality assurance of the QA device.