Development Of Real-Time Monitoring System For Proton Pencil Beam Spot Position Using Fiber-Optic Cerenkov Radiation Sensor Array

PBS, recently developed, scans a tumor with very precise beam of protons that’s accurate within millimeters, sparing the healthy surrounding tissues. However, it is able to harmful rather than conventional radiotherapy if the beam is not accurately irradiated as planned. It is very important to measure spot profiles of the proton pencil beam for the accurate delivery of dose to the target volume with a good conformity We have developed a fine segmented detector array to monitor PBS. A prototype beam monitor using Array of Fiber Optic Cerenkov Radiation Sensor (AFCRS) has been developed for real-time display of the pencil beam status during the PBS mode operation. The x-y monitoring system with 128 channel readout is mounted to the snout for the in-situ real time monitoring. Spot profiles of various energies are measured. Two dimensional Gaussian fit is used to analyze the beam width and the spot center. The ability of this system to evaluate Lynx system (Scintillator-based sensor with CCD camera) and EBT3 for PBS was compared. The measured Gaussian widths using AFCRS changes from 13 to 5 mm for the beam energies from 100 to 226 MeV. The spot size of PBS using the AFCRS is well matched with the data acquired by a Lynx system and EBT 3 film. The dosimetric performance of the newly developed system based on AFCRS was comparable to that of the Lynx system and EBT3 film. Not only measuring the spot profile but also monitoring dose map by accumulating each spot measurement will be available.