Design calculations of a 252CF source based thermal neutron irradiation setup for BNCS

Full text: Boron neutron capture therapy (BNCT) is a promising technique for the treatment of malignant disease targeting organs of the human body. In BNCT, thermal neutrons are used to treat superficial tumors. A prime example is Boron Neutron Capture Synovectomy (BNCS), in which thermal neutrons are absorbed in boron compound injected in synovium tissue, located 1.5 to 2.0 cm below the surface of the skin of rheumatoid arthritis patients. Monte Carlo calculations were carried out to design a thermal neutron irradiation set-up using the MCNP code. The set-up consists of a 252Cf source enclosed in a polyethylene moderator. A graphite reflector surrounding the moderator is used to enhance the thermal to fast neutrons intensity ratio from the set-up. The geometry of the set-up is optimised to obtain maximum ratio of thermal to fast neutrons intensity. The optimum length of the moderator was found to be 14 cm, with the neutron source positioned at a distance of 4.9 cm from the moderator-end. Due to encasing of the moderator assembly within graphite collar and a graphite disk cover on the back of the moderator, the thermal to fast neutron intensity ratio has improved by 80 %. Results on optimum geometry of the set-up and the corresponding thermal to fast neutron intensity ratio will be reported. Results of the ultimate dose delivered to synovium tissue, will also be discussed