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A Protocol for Comprehensive Acceptance/Commissioning of Complex 3D QA Devices

J O'Daniel

J O'Daniel*, L Ren, H Yan, F Yin, Duke University Medical Center, Durham, NC

SU-E-T-70 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

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 <19%). End-to-end testing showed robust results (>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 be applicable to any clinic. This protocol can be used as a baseline for quality assurance of the QA device.

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