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In-Vivo Diode Dosimetry Proton Therapy Range Verification Validation Study for Pediatric CSI

A Toltz

A Toltz1*, M Hoesl2 , J Schuemann2 , J Seuntjens1 , H Lu2 , H Paganetti2 , (1) McGill University, Montreal, Quebec, (2) Massachusetts General Hospital, Boston, MA


SU-E-T-524 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: With the aim of reducing acute esophageal radiation toxicity in pediatric patients receiving craniospinal irradiation (CSI), we investigated the implementation of an in-vivo, adaptive proton therapy range verification methodology. Simulation experiments and in-phantom measurements were conducted to validate the range verification technique for this clinical application.

Methods: A silicon diode array system has been developed and experimentally tested in phantom for passively scattered proton beam range verification for a prostate treatment case by correlating properties of the detector signal to the water equivalent path length (WEPL). We propose to extend the methodology to verify range distal to the vertebral body for pediatric CSI cases by placing this small volume dosimeter in the esophagus of the anesthetized patient immediately prior to treatment. A set of calibration measurements was performed to establish a time signal to WEPL fit for a “scout” beam in a solid water phantom. Measurements are compared against Monte Carlo simulation in GEANT4 using the Tool for Particle Simulation (TOPAS).

Results: Measurements with the diode array in a spread out Bragg peak of 14 cm modulation width and 15 cm range (177 MeV passively scattered beam) in solid water were successfully validated against proton fluence rate simulations in TOPAS. The resulting calibration curve allows for a sensitivity analysis of detector system response with dose rate in simulation and with individual diode position through simulation on patient CT data.

Conclusion: Feasibility has been shown for the application of this range verification methodology to pediatric CSI. An in-vivo measurement to determine the WEPL to the inner surface of the esophagus will allow for personalized adjustment of the treatment plan to ensure sparing of the esophagus while confirming target coverage.

Funding Support, Disclosures, and Conflict of Interest: A Toltz acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290).

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