Secondary Neutron Doses to Pediatric Patients During Intracranial Proton Therapy: Monte Carlo Simulation of Neutron Energy Spectrum and Organ Doses

Apr 19, 2026

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Monte Carlo simulations using PHITS evaluated secondary neutron energy spectra and resulting organ doses during intracranial proton therapy in a hybrid phantom of a 5-year-old boy. Secondary neutron doses decreased with increasing distance from the treatment field. The neutron spectrum showed three energy peaks at about 10−7, 1, and 100 MeV. A block collimator and patient collimator significantly affected organ doses, with secondary neutrons from the patient collimator markedly higher than from the first scatter, indicating the need for proactive protection in beam-line design.

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Apr 19, 2026