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Using In-Vivo EPID Measurements to Improve Bowel Toxicity Modeling

V Moiseenko*, T Nelson, D Simpson, C Bojechko, University of California San Diego, La Jolla, CA

Presentations

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

Room: AAPM ePoster Library

Purpose: For gastrointestinal treatments, excess dose to the bowel can result in acute toxicities. Current estimates of bowel toxicity is based on pre-treatment dose volume histogram data. However, the actual dose the bowel receives can depend on intrafraction variations such as patient anatomy changes. We propose a method to model bowel toxicities, incorporating in-vivo patient information using transit EPID images.

Methods: For 63 patients treated to the lower thorax, abdomen or pelvis on the Varian Halcyon, chart review was performed to measure incidences of acute gastrointestinal toxicity (diarrhea) for each week of treatment. For each treatment plan, the absolute volume DVH of the bowel was exported and analyzed. For each fraction of treatment in vivo EPID images were collected and compared to the images collected on the first fraction of treatment. For a small subset of patients with and without toxicities, the in-vivo EPID images over the course of treatment were analyzed.

Results: The incidence of toxicity versus the volume of 40 Gy was fitted with a logistic function, which was superior to an average model (p < 0.0001) and agrees with previously published models. For the in-vivo EPID images it was observed that for incidences of toxicities, there were systematic trends during the course of treatment suggesting potential biases during the course of treatment resulting in a change to bowel dose.

Conclusions: Data from treatment planning DVH’s shows that the incidence of bowel toxicities increases with the volume of bowel receiving 40 Gy following a logistic model. Using in-vivo EPID images to monitor patient anatomy changes provides additional per fraction information. A full analysis of the collected EPID images will be performed to assess if it is superior to DVH methods.

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Funding Support, Disclosures, and Conflict of Interest: C. Bojechko receives grant funding from Varian Medical Systems.

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