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Automated Daily EPID Exit Dose Analysis Uncovers Treatment Variations


A Olch

A Olch*, University of Southern California, Los Angeles, CA

Presentations

SU-E-T-139 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall


Purpose:To evaluate a fully automated EPID exit dose system for its ability to detect daily treatment deviations including patient setup, delivery, and anatomy changes.

Methods:PerFRACTION (Sun Nuclear Corporation) software is a system that uses integrated EPID images taken during patient treatment and automatically pulled from the Aria database and analyzed based on user-defined comparisons. This was used to monitor 20 plans consisting of a total of 859 fields for 18 patients, for a total of 251 fractions. Nine VMAT, 5 IMRT, and 6 3D plans were monitored. The Gamma analysis was performed for each field within a plan, comparing the first fraction against each of the other fractions in each treatment course. A 2% dose difference, 1 mm distance-to-agreement, and 10% dose threshold was used. These tight tolerances were chosen to achieve a high sensitivity to treatment variations. The field passed if 93% of the pixels had a Gamma of 1 or less.

Results:Twenty-nine percent of the fields failed. The average plan passing rate was 92.5%.The average 3D plan passing rate was less than for VMAT or IMRT, 84%, vs. an average of 96.2%. When fields failed, an investigation revealed changes in patient anatomy or setup variations, often also leading to variations of transmission through immobilization devices.

Conclusion:PerFRACTION is a fully automated system for determining daily changes in dose transmission through the patient that requires no effort other than for the imager panel to be deployed during treatment. A surprising number of fields failed the analysis and can be attributed to important treatment variations that would otherwise not be appreciated. Further study of inter-fraction treatment variations is possible and warranted.

Funding Support, Disclosures, and Conflict of Interest: Sun Nuclear Corporation provided a license to the software described.


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