Development of In situ Dosimetry for FLASH Proton Radiotherapy via Organic Scintillating Fibers.

A study on the design, development, and preliminary proof-of-concept testing of a dosimetry device intended for use in FLASH radiotherapy is presented here. The system utilizes organic scintillating fibers in conjunction with a silicon photomultiplier (SiPM) and field-programmable gate array (FPGA) to provide real time measurements of dose and pulse monitoring in situ during radiotherapy treatment delivery. Simulations utilizing GEANT4 aided in discovering a geometrical design of the fibers (i.e., the appropriate diameter) which indicated minimal beam perturbations with the scintillating material in place when compared to measured values of a clinical proton beam with no in-beam material at the Huntsman Cancer Institute (HCI) at the University of Utah. Measurements with a portable X-ray machine provided a strong correlation between the measured charge integration of the system and actual dose provided by the X-ray machine (up to approximately 35 mrem s-1), and these measurements also indicated the possibility of response on a sufficient timescale (on the order of nanoseconds) to trigger a safety interlock at a specified dose threshold with minimal latency and dose error. Preliminary irradiations were performed with the proton beam at HCI which indicated the capability of the dosimetry system to provide individual pulse monitoring, which would be of major benefit to FLASH research as well as traditional treatments methods.