Room: Track 3
Purpose: To develop a new dosimetry method for rapid reconstruction of out-of-field neutron dose to patients in pencil beam scanning (PBS) proton therapy for large-scale proton patient dosimetry required in epidemiologic studies of late effects.
Methods: The dosimetry method is based on neutron dose voxel kernels (DVKs) generated by TOPAS MC simulations of a proton pencil beam irradiating a water phantom (60 × 60 × 300 cm3). The DVKs were generated with respect to 19 beam energies (from 70 to 250 MeV with the 10-MeV interval) and three range shifter thicknesses (1, 3, and 5 cm). An in-house program was written in C++ to superimpose the DVKs onto a patient CT images according to proton beam information (energy, position, and direction) given in the patient treatment plan. The DVK dosimetry method was tested by calculating organ/tissue-specific neutron doses of 1- and 5-year-old whole-body computational phantoms resulting from intracranial and craniospinal irradiations.
Results: The calculated dose values generally showed a good agreement with those calculated by direct MC simulations with a dedicated PBS MC model. The dose differences from the MC simulations for most organs and tissues were less than 30% and 10% for the intracranial and craniospinal irradiations, respectively. The computation time of the DVK method per one patient case was in a range of 1–30 minutes on a single CPU core of a personal computer, demonstrating the significant improvement in computation efficiency against the full MC simulation that required several days even on 1500 CPU cores of a high-performance computing cluster.
Conclusion: The developed DVK method can rapidly estimate out-of-field neutron dose of PBS patients with accuracy comparable with direct MC simulation. The DVK method as the first application will be used to reconstruct normal tissue doses of large-scale pediatric patients enrolled in the Pediatric Proton/Photon Consortium Registry (PPCR).