Phantom materials for boron neutron capture therapy

The aim of this work was to establish which reference phantom material is m ost suited for dosimetry under reference conditions of neutron beams for bo ron neutron capture therapy (BNCT). For this purpose, phantoms of dimension s 15 x 15 x 15 cm(3) and 30 x 30 x 30 cm3 composed of water, tissue-equival ent (TE) liquid, polyethylene (PE), polymethyl methacrylate (PMMA) and wate r containing 10 mu g g(-1) and 30 mu g g(-1) B-10 were irradiated using the Petten BNCT beam. Activation foils and a diode detector were used for the determination of the thermal neutron fluence rate. The gamma-ray dose rate and the fast neutron dose rate were determined using paired ionization cham bers. In water, PMMA and TE liquid the absolute dose and fluence values agreed wi thin 3% at a reference depth of 2 cm, with the exception of the gamma-ray d ose rate in PMMA, which was 12% lower than in water. Due to a higher hydrog en concentration in PE compared with wafer, the dose and fluence: values in PE differed more than 30% from those in water. Only minor differences were observed between the percentage depth dose curves for the various dose com ponents in water, PMMA and TE liquid. The addition of 10 mu g g(-1) and 30 mu g g(-1) B-10 to water resulted in a decrease in the absolute thermal neu tron fluence at 2 cm depth of about 2% and 8%, respectively, and a decrease d penetration of thermal neutrons at depth for the 30 mu g g(-1) B-10 conce ntration. For reference dosimetry of an epithermal neutron beam for BNCT, both water and TE liquid are suitable phantom materials. For practical reasons, water is therefore proposed as reference phantom material. For measurements requi ring a solid phantom, PMMA is proposed.