SU‐E‐T‐139: Automated Daily EPID Exit Dose Analysis Uncovers Treatment Variations

Abstract

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.Sun Nuclear Corporation provided a license to the software described.