Enhancement of the Absorbed Dose in a d(14) + Be Fast-Neutron Beam by 10B Neutron-Capture Therapy

Abstract

Boron neutron-capture therapy uses the chemical delivery of specific boron compounds to neoplastic tissue in combination with thermal neutrons to produce an enhanced radiation dose in the tumor. The nuclear fission reaction when 10B is irradiated with slow neutrons releases relatively large amounts of high linear energy transfer radiation through its fission products 7Li and stripped helium nuclei. The short range of these particles (approximately 10 μm) theoretically restricts the radiation dose to tumor cells. Because of the rapid attenuation of thermal neutrons in tissue, this treatment modality needs surgical techniques to expose the tumor directly to the thermal neutron beam (Hatanaka et al. 1991). On the other hand, neutrons of all energies become thermalized by their interaction with the target material. Hence, during fast-neutron therapy, low-energy neutrons are present in tissue. Since 1978 a compact cyclotron has been used at the Essen University Hospital for fast-neutron therapy. The neutrons are produced by bombarding a beryllium target with 14 MeV deuterons. The poor depth dose distribution of this beam (median energy 5.7 MeV) limits the treatment of deep-seated tumors (Rassow 1982). An enhancement of the dose at depth could be obtained by neutron-capture reactions if there is a sufficient flux of thermalized neutrons derived from fast neutrons after slowing down in tissue.