Maximum therapeutic depth in thermal neutron capture therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Medicine

Background:

• Boron Neutron Capture Therapy (BNCT) is a binary treatment modality.
• Effective treatment depth in thermal neutron BNCT is contingent upon beam aperture, heavy water concentration, and boron concentrations.

Purpose of the Study:

• To evaluate the maximum therapeutic depth in the brain for thermal neutron BNCT using BSH (boronophenylalanine) and D,L-BPA (boronophenylalanine).
• To analyze the impact of key parameters like boron concentrations and heavy water on treatment efficacy.

Main Methods:

• Utilized human pharmacokinetic data for BSH and D,L-BPA.
• Employed experimental dose-depth phantom data from the Musashi Institute of Technology reactor.
• Calculated therapeutic depths based on tumor-to-blood boron ratios and normal tissue tolerance dose (15 Gy).

Main Results:

• Average tumor-to-blood boron ratios were 1.4 (0.4) for BSH and 4.3 (1.8) for D,L-BPA in subcutaneous melanoma.
• Maximum therapeutic depth was calculated to be approximately 1.5 cm for both BSH and D,L-BPA in brain treatments.
• A 15% heavy water concentration increased treatment depth by 0.5 cm, but this was counteracted by smaller beam apertures.

Conclusions:

• The maximum therapeutic depth for thermal neutron BNCT in the brain is limited, approximately 1.5 cm for both BSH and D,L-BPA.
• Optimizing boron delivery and beam characteristics is crucial for enhancing BNCT treatment efficacy.
• Further research may explore enhanced uptake in specific neural tracts for improved outcomes.