Measurement of augmentation of 252Cf implant by 10B and 157Gd neutron capture.

252Cf has been used as a brachytherapy source since the early 1970s. The dominant mechanism of interactions of 252Cf neutrons with tissue is elastic scattering. The scattered neutrons lose part of their energy, which is released as kinetic energy of the recoiling nuclei. By multiple scattering, neutrons lose their energy and eventually become thermalized (in energetic equilibrium with tissue atoms with an average energy of 0.025 eV) and do not play any role in radiotherapy. These thermal neutrons may interact with hydrogen nuclei or with nitrogen, but the cell killing effects by these reaction products are negligibly small compared to the elastic scattering by fast neutrons or by photons emitted by californium. Nonetheless, these thermal neutrons are still potentially usable for neutron capture therapy and can be used to enhance californium brachytherapy effects. Neutron capture therapy is a two-part therapy relying on the selective loading of tumor cells with compounds containing 10B or 157Gd and subsequent irradiation with thermal neutrons. To calculate neutron capture doses one has to know thermal neutron flux. This paper presents results of an experimental study of thermal neutron flux and calculations of boron neutron capture and gadolinium neutron capture doses in the vicinity of 252Cf sources.