Neutron Activation Dose Assessment Based on a Human Head Phantom Post-BNCT

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Medicine

Background:

• Boron Neutron Capture Therapy (BNCT) is an advanced radiation therapy for cancer.
• Understanding residual radioactivity in patients post-BNCT is crucial for safety assessments.
• Previous studies identified sodium-24 (24Na), chlorine-38 (38Cl), and potassium-42 (42K) as residual nuclides.

Purpose of the Study:

• To assess residual radioactivity in a human head phantom after BNCT neutron source irradiation.
• To identify the primary contributing nuclides to internal exposure dose post-irradiation.
• To evaluate the effective dose and external dose rate from the activated phantom.

Main Methods:

• Utilized Monte Carlo software for simulating neutron irradiation of a head phantom (ICRP Publication 110).
• Calculated residual radioactivity and internal exposure dose from activated nuclides.
• Analyzed the dose rate at a distance of 60 cm from the activated phantom over time.

Main Results:

• Phosphorus-32 (32P) was identified as the nuclide contributing most to internal exposure dose, in addition to 24Na, 38Cl, and 42K.
• The effective dose from 60 minutes of irradiation activation ranged from 148 to 401 μSv, indicating a low level.
• The dose rate at 60 cm decreased below 1 μSv/h within 5 minutes post-irradiation due to the decay of short-lived nuclides (e.g., 19O, 20F).

Conclusions:

• Phosphorus-32 is a significant contributor to internal dose in patients undergoing BNCT with this neutron source.
• The calculated effective dose and external dose rates post-irradiation are within safe limits.
• Residual radioactivity from BNCT using a 2.8 MeV proton accelerator-based neutron source poses a minimal radiation hazard.