Beam collimation and bolusing material optimizations for 10boron neutron capture enhancement of fast neutron (BNCEFN):: Definition of the optimum irradiation technique

Purpose: In boron-10 neutron capture enhancement of fast neutron irradiation (BNCEFN), the dose enhancement is correlated to the B-10 concentration and thermal neutron flux. A new irradiation technique is presented to optimize the thermal neutron flux. Methods and Materials: The coupled FLUKA and MCNP-4A Monte Carlo codes were used to simulate the neutron production and transport for the Nice and Orleans facilities. Results: The new irradiation technique consists of a 20-cm lead blocks additional collimator, placed close to the patient's head, which is embedded in a pure graphite cube, A 24-fold thermal neutron flux increase is calculated between a 5 x 5 cm(2) primary collimated field, with the patient's head in the air, and the same field size irradiated with the optimum irradiation technique. This increase is more important for the p(60)+Be Nice beam than for the p(34)+Be Orleans one. The thermal neutron Bur is 2.1 x 10(10) n(th)/Gy for each facility. Assuming a 100 mu g/g B-10 concentration, a physical dose enhancement of 22% is calculated. Moreover, the thermal neutron flux becomes independent of the field size and the phantom head size, Conclusion: This technique allows conformal irradiation of the tumor bed, while the thermal neutron flux is enhanced, and spreads far around the tumor. (C) 1999 Elsevier Science Inc.