Development of a Daily-Treatment Beam-Monitoring System Based Gafchromic EBT3 Film for Pencil-Beam Scanning Proton Therapy

This study describes the development of a simple method to assess inter-fractional deviations of delivered proton beams in treatment rooms. To monitor the treatment beam, we measured the field-by-field beam fluences by attaching the EBT3 film to the snout, followed by a simple constancy check based on comparisons between the reference beam fluences (acquired during the pre-treatment quality assurance process) and the test beam fluences (acquired during treatment). The feasibility of the proposed treatment beam-monitoring system was confirmed by evaluating 12 treatment fields for each of six patients (brain, liver, prostate, lung, cranial and spinal area, and head and neck). The constancy of the treatment beams was verified by using a gamma index analysis to compare three measurements per field with the reference beam fluence. On the basis of the 3%/3 mm criterion, the average gamma-index passing rates for all measurements were over 99.6%. These results suggest that the constancy of fractional proton beams delivered to patients in treatment rooms can be verified with EBT3 film-based proton-beam monitoring system that can be easily attached to the treatment nozzle and is cost effective.