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Beyond Catching Big Errors: Implementation and Clinical Use of a Commercial EPID Dosimetry Platform to Quantify Small Daily Clinical Treatment Variations and Trends

S Dieterich

S Dieterich*, D Hernandez , S Benedict , R Fragoso , S Rao , UC Davis Cancer Center, Sacramento, CA


SU-I-GPD-T-258 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: In-house EPID dosimetry systems have been developed in large academic centers, however these technologies are not transferable to smaller clinics. In this study we evaluate a new commercial EPID Dosimetry platform in terms of commissioning requirements, practicality, and capability to detect significant errors during an individual patient’s treatment course.

Methods: Two studies were utilized for this evaluation. (1) A pilot study on canine cadaver heads was performed in Veterinary Radiation Oncology to establish workflow and QA parameters, and the results were used as baseline for this study. (2) Under IRB approval, data from 17 cranial and 20 H&N human patients was collected. For all studies, the EPID-based patient QA (DQA) results were compared to the device-based DQA. All treated fractions were analyzed using backprojection on the simulation image to provide a DVH of delivered dose. In-vivo EPID QA protocols were developed based on planning constraints.

Results: EPID-based DQA was consistent (± 3%) with device-based DQA, saving 15 min per QA device setup. 2D EPID shifts in early data analysis lead to the discovery of a problem in the MV panel electronics. EPID-based DVH calculations for all cranial fractions confirmed that dosimetric effects of intrafraction motion to be are small, i.e. our clinic's PTV margins are appropriate. For H&N patients, OARs or targets failed the QA tolerance in <10% of fractions. The dosimetric impact of a known setup challenge in one H&N patient was quantified. QA pass rate trend changes confirmed plan adaptation timing in another case. Clinical workflow issues were the main cause of missing in-vivo EPID data (29%).

Conclusion: Commercial EPID dosimetry software allows medium-sized clinics to implement in-vivo EPID QA. Cost of the software and physics FTE for commissioning and clinical implementation compare favorably to device-based DQA. Daily in-vivo QA quantifies patient changes for precision clinical decision-making.

Funding Support, Disclosures, and Conflict of Interest: The research was performed using beta testing software provided by Sun Nuclear Inc.

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