Performance comparison of 7Li(p,n) and 3H(p,n) reaction-based BNCT setups

Full text: Boron Neutron Capture Therapy (BNCT) is a therapeutic modality for cancer treatment. Epithermal neutrons are used in BNCT to treat deep-seated tumours in organs of the human body. Li(p,n) and H(p,n) reactions, are ideally suited for their application in producing epithermal neutrons for BNCT treatment of brain and head cancer treatment. In this study, Monte Carlo simulations were carried out to compare the performance of accelerator based BNCT set-ups utilizing Li(p,n) and H(p,n) reaction to produce epithermal neutrons for the treatment of brain tumours. The set-up consists of a polyethylene moderator, enclosing a neutron target, to produce epithermal thermal neutrons and a double truncated collimator to collimate the neutron beam to a region of interest in the brain. The ratio of epithermal to (fast + thermal) neutron intensities from the set-up, depends upon the moderator length and position of the source inside the moderator. Monte Carlo calculations were carried out to optimise the dimensions of the set-up to produce a maximum ratio of epithermal to fast neutron intensity at the location of the brain sample. For the 7Li(p,n) reaction based set-up, a value of 1.80 has been observed for epithermal to (fast+thermal) neutrons intensity ratio a for an optimum moderator-length of 8 cm, with the source positioned at a distance of 1 cm from the moderator end. Although neutrons from H(p,n) reaction have three times higher energies than those from the 7Li(p,n) reaction, yet the optimum values of the geometry parameter and the ultimate epithermal to (fast+thermal) neutrons intensity ratio from the 3H(p,n) reaction based set-up are similar to those for the Li(p,n) reaction based set-up. Results of these studies will be discussed along with the ultimate neutron dose delivered to brain tumour tissue for both set-ups