RADIOCHROMIC FILM DOSIMETRY FOR VERIFICATION OF DOSE DISTRIBUTIONS DELIVERED WITH PROTON-BEAM RADIOSURGERY

In this work we studied the feasibility of radiochromic him for dosime try verification of proton Bragg peak stereotactic radiosurgery with m ultiple beams. High-sensitivity MD-55 radiochromic film was calibrated for proton beam irradiation and the RIT 113 system was employed for h im evaluation. Simulated stereotactic radiosurgery with a special phan tom arrangement for film dosimetry was performed, following the same p rocedure as for a patient undergoing treatment. Five-beam irradiation was developed using a 3D treatment planning system. This plan was then delivered to the phantom in a one-day experiment. Planned and measure d composite dose distributions were compared. Spatial accuracy of dose delivery to a region containing a simulated critical structure was ev aluated for a single portal. Radiochromic film dosimetry validated the prescribed dose delivery within +/-5%, one standard deviation, by com paring calculated doses with measured values. The alignment of apertur es and boluses, as well as the alignment of the phantom with respect t o the isocentre, was confirmed. Spatial accuracy of the method would h ave been able to detect possible misalignments greater than +/-2 mm. W e have demonstrated how radiochromic film dosimetry can be used to mea sure complex dose distributions in an irradiated phantom, thus enablin g us to verify planned dose delivery of proton Bragg peak stereotactic radiosurgery with multiple beams. We assume that the dosimetric agree ment between planned and measured dose distributions for the reported simulations will apply to patient treatments.