Numerical optimisation of the fission-converter and the filter/moderator arrangement for the Boron Neutron Capture Therapy (BNCT)

Boron Neutron Capture Therapy (BNCT) [4, 5] is a form of a radiation therapy used for treatment of some kinds of cancer (mainly glioblastoma multiforme) which, due to their character, are hard to be extracted with surgical methods. The BNCT method involves the delivery of a capture compound − the B isotope is usually used – which preferentially concentrates in the cancer tissue, followed by the irradiation of the patient with epithermal neutrons. The incident neutrons are moderated in patient’s body to thermal energies and cause the B(n,α)Li reaction. The reaction products, i.e. Li and α particles, deposit their energies on the reaction spot – typically within ~10 μm of the reaction origin. When concentration of the B isotope in the cancer tissue is considerably larger than in the healthy tissue, a proportionally higher radiation dose is delivered to the tumour and makes the method effective. During the therapy, an adequate number of epithermal neutrons incident patient’s skin in a suitable time should be provided. One estimates [4] that the time of irradiation does not exceed 10÷15 min when the epithermal neutron flux is at least 10 n/cm⋅s at the therapy position. Currently, clinical trials of the BNCT method utilise nuclear reactors as the neutron source. The MARIA reactor is to be used for the planned Polish BNCT facility. Because intensity of neutron flux at the outlet of the reactor duct does not meet the therapy requirements (mainly thermal energies) it is essential to use a neutron converter, which contains a fissionable material. Fast neutrons from the U fission will be slowed down using a filter/moderator set-up. Photon and fast neutron doses should be suitably reduced with some filters not to exceed 10% epithermal neutron dose. Numerical optimisation of the fission-converter and the filter/moderator arrangement for the Boron Neutron Capture Therapy (BNCT) Grzegorz Tracz, Ludwik Dąbkowski, Dominik Dworak, Krzysztof Pytel, Urszula Woźnicka