Comparative analysis of induced radioactivity in treatment room using FLUKA Monte Carlo simulation

The Monte Carlo code, FLUKA, was used to compute the induced radioactivity in treatment room for proton therapy, carbon ion therapy, and boron neutron capture therapy. For modeling activity buildup, a periodic irradiation activity buildup approach was employed. Results show that air activation levels from all three therapies are extremely low. In patients, proton/carbon ion therapy mainly generates short-lived isotopes like ^15O, with dose rates at 1 m distance from patient dropping below 0. 1 \, ^-1 within 30 minutes. Boron neutron capture therapy, however, produces longer-lived isotopes (^24N, ^38Cl), leading to elevated dose rates for several hours and requiring post-treatment control measures. Notably, concrete activation diverges significantly: for proton/carbon ion therapy, the induced activity remains low (10^7 \, Bq), posing minimal risks to radiation exposure or waste disposal. Boron neutron capture therapy, by contrast, increases concrete activation by two orders of magnitude. After one week of operation, 24Na buildup causes the dose rate at the treatment room center to reach 39. 5 \, ^-1 (after 5 minute cooling) -15 times the conventional limit (2. 5 \, ^-1). After 30 years of operation and one month of shutdown, the activity of ^55Fe exceeds the exemption limit by a factor of 42. 1. This study provides key guidance for radiation shielding design, waste management, and clinical protocol optimization for advanced radiotherapy facilities.