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Assessing the Effect of Multiple Delivery Parameters in Patient-Specific QA for Poor Pass-Rates Using A Diode Array and Treatment Plans From Two Different Planning Systems

J Bogue*, E Parsai, University of Toledo Medical Center, Toledo, OH


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To evaluate patient-specific quality assurance procedures performed on a cylindrical diode array for common delivery parameters that produce poor pass-rates with two different treatment planning systems.

Methods: 26 total patient-specific quality assurance results were evaluated at 2%/2mm gamma analysis with a 10% threshold. Two different treatment planning systems were compared using 13 patients from each treatment planning system. Quality assurance results were evaluated against the following: average and maximum gantry speed; maximum, average, and average non-zero jaw speed; maximum, average, and average non-zero dose rate ramping between control points; maximum, minimum, and average dose rate; maximum, minimum, and average field size; and duty cycle (monitor units divided by prescribed dose). All plans were planned and delivered as volumetric modulated arc therapy with a variety of plan types, used to evaluate a wide range of field sizes. Energies used were 6 MV, 6 FFF, 10 MV, or 10 FFF. If couch kicks were present in the plan, they were overridden to zero for the quality assurance plan and delivery to avoid irradiating the cylindrical diode array’s electronics.

Results: All evaluation parameters were plotted against the pass-rate to determine any immediate relationship between the delivery parameter and pass-rate. No immediate relationship was discernable between gantry speed, duty cycle, dose rate, or jaw speed parameters and pass-rate for both planning systems. For field size, there is an obvious trend for both planning systems of poorer results at smaller and larger field sizes, with better pass rates near 100cm2. Small changes in dose rate also seemed to produce poorer pass-rates without a clear trend.

Conclusion: Multiple delivery parameters were evaluated to trend against quality assurance results to identify common failure modes. In this brief study, field size and small changes to dose rate displayed an observable impact on patient specific quality assurance results.


Intensity Modulation, Quality Assurance


TH- External Beam- Photons: Quality Assurance - IMRT/VMAT

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