Prospect of Using The Photoneutron Beam Component from High Energy linacs in BNCT, A Monte Carlo Simulation

One drawback in widely using neutron capture therapy (NCT) is the limited number of appropriate neutron source facilities. At present neutron sources for clinical NCT are mainly research reactors. However most reactors are not in close proximity to hospitals and their use for clinical trials can be difficult. Other suggested sources include dedicated single-purpose reactors, accelerator-based neutron sources and ²⁵²Cf isotopic sources. This study examines the potential of using the photoneutrons produced from medical linacs, which are embedded in hospital environments for radiotherapy, as a source for NCT. Preliminary simulation using MCNPX simulation were conducted to calculate the photoneutron flux of a medical linac head with the aim of maximizing the thermal and epithermal neutron component whilst minimizing the photon contribution from the primary beam. Further simulations were conducted to determine the most feasible conditioning methods. Target desirable minimum neutron beam fluence rate should be 10 ⁹ cm^-2 s^-1 according to IAEA guidelines. Although beams of 5 times 10⁸ cm^-2 s ^-1 are useable, they result in rather long irradiation times as current experience show. In existing facilities the range of dose from epithermal neutrons is from 2.5 to 13 times 10^-13 Gy cm² per neutron. A target value should be 2 times 10^-13 Gy cm² per epithermal neutron. The goal of this work was to produce neutrons that meet these treatment conditions