Phantom materials for boron neutron capture therapy

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Nuclear Medicine

Background:

• Accurate dosimetry is crucial for Boron Neutron Capture Therapy (BNCT) treatment planning and delivery.
• Reference phantom materials are essential for standardizing neutron beam dosimetry under reference conditions.
• Previous studies have not definitively established the optimal phantom material for BNCT dosimetry.

Purpose of the Study:

• To determine the most suitable reference phantom material for dosimetry of neutron beams used in BNCT.
• To compare the dosimetric properties of water, tissue-equivalent liquid, polyethylene, and PMMA.
• To evaluate the impact of boron concentration on neutron fluence and dose distribution.

Main Methods:

• Irradiation of 15x15x15 cm³ and 30x30x30 cm³ phantoms made of water, TE liquid, PE, PMMA, and boron-doped water (10 and 30 µg/g).
• Measurement of thermal neutron fluence rate using activation foils and a diode detector.
• Determination of gamma-ray and fast neutron dose rates using paired ionization chambers.

Main Results:

• Water, PMMA, and TE liquid showed agreement within 3% for absolute dose and fluence at 2 cm depth, except for PMMA's lower gamma-ray dose (12% less than water).
• Polyethylene (PE) showed >30% difference in dose and fluence compared to water due to higher hydrogen concentration.
• Boron doping in water (10 and 30 µg/g) decreased thermal neutron fluence at 2 cm by 2% and 8%, respectively, and reduced penetration at depth for 30 µg/g.

Conclusions:

• Both water and tissue-equivalent liquid are suitable reference phantom materials for epithermal neutron beam dosimetry in BNCT.
• Water is recommended as the primary reference phantom material for practical reasons.
• PMMA is proposed as a suitable solid phantom material, with the caveat that its lower gamma-ray dose must be considered.