Program Information
An Image Guided Radiotherapy (IGRT) Method to Rapidly Identify Patients with Important Prostate Inter-Fraction Motion
O Piron*, N Varfalvy , L Archambault , CHUQ Pavillon Hotel-Dieu de Quebec, Quebec, QC
Presentations
TU-C1-GePD-JT-5 (Tuesday, August 1, 2017) 9:30 AM - 10:00 AM Room: Joint Imaging-Therapy ePoster Theater
Purpose: In prostate cancer treatment using radiation therapy, motion and volume variations of the prostate and organs at risk (OAR) can cause errors between the planned and the delivered dose distributions and increase the risk of toxicity. A method based on EPID gamma analysis categorization method makes it possible to quickly detect cases requiring more careful supervision and frequent imaging.
Methods: EPID dose images were acquired at every fraction for 58 patients. A gamma analysis was performed relative to the first fraction. Multiple parameters were extracted from the daily gamma map. The evolution of these parameters was characterized to identify categories of risk for inter-fraction motion with a hidden Markov model (HMM). These categories indicated the degree of errors of the daily treatment. A linear regression of the mean category of the first 5 fractions was made to predict the final state of the patient.
Results: Four categories of risk were identified and sorted in increasing level of inter-fraction motion. During treatment, patients either remain in their category or migrated to a higher one. Patients in category 1 at the start of treatment had 100% of chance to remain in category 1 or 2; patients in category 2 had 88% of chance to finish in category 1 or 2; patients in category 3 had 85% of chance to finish in category 3 and patients in category 4 had 100% chance to remain in the same category. Thus, the initial category is a strong indicator of the overall patient behavior.
Conclusion: Analysis of daily EPID images provides a rapid method to identify patients at risk or not of inter-fraction motion and help to set up the monitoring adapted to each category. The next step is to correlate the dose received by the prostate and the OARs with our risk categories.
Funding Support, Disclosures, and Conflict of Interest: This work was funded in part by Varian Medical Systems
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