Evaluation of an Integrated Radiochromic Film in vivo Dosimetry System for Proton Therapy
Abstract
Purpose
In vivo dosimetry is essential for treatment verification and patient safety. Although commercial radiochromic film systems are established for photons, proton therapy adds complexity because film response is energy dependent and clinical beams are typically polyenergetic. The goal of this study was to evaluate the feasibility and performance of an in vivo film-based dosimetry system (Ashland Inc., Wilmington, DE) for proton therapy, with emphasis on energy-dependent calibration strategies and validation under clinically relevant proton beam geometries.
Methods
Calibration curves (0-300 cGy) were acquired using monoenergetic proton beams at clinical energies (70, 110, 160, 200 MeV). The post-irradiation film response was sampled every 5 minutes during the first hour, and then hourly up to 24 hours. Validation measurements of 125 and 175 cGy were performed with the same geometry as the calibration irradiations. An anthropomorphic breast phantom was then used to simulate in vivo clinical irradiation conditions for four representative proton treatment plans. Doses at five points on the phantom were measured using the film dosimeters and compared with expected doses from TPS. The impact of calibration-curve selection on the derived dose was quantified.
Results
Calibration validation yielded ~10% maximum difference and 3.76% median absolute percent difference. Simulated clinical measurements with the anthropomorphic phantom were also accurate, as the median absolute percent difference was 3.97%. Measured doses differed by up to 12% from the TPS dose, depending on which calibration curve was used for readout.
Conclusion
Commercial radiochromic film–based in vivo dosimetry is feasible for proton therapy when energy-dependent calibration strategies are employed. The observed dependence of measured dose on calibration curve energy underscores the need for energy-specific commissioning and appropriate calibration selection to ensure accurate in vivo dose verification. This work opens opportunities for potential application of this system for dose monitoring in proton therapy.