A neutronic study of an accelerator-based neutron irradiation facility for the treatment of superficial melanoma by boron neutron capture therapy

Previously, a neutronic study of an accelerator-based epithermal neutron irradiation facility (AENIF) for boron neutron capture therapy (BNCT) was performed using three-dimensional Monte Carlo transport calculations. The major components of the AENIF are a radio-frequency quadrupole proton accelerator, a 7Li target, and a moderator assembly. Neutrons are generated by bombarding the bombarding the 7Li target with 2.5-MeV protons. The neutrons emerging from the 7Li target are too energetic to be used for BNCT and are moderated as they traverse the moderator assembly to the patient. The design of a moderator assembly for an AENIF for the treatment of glioblastoma is reviewed, and this design is compared with the design of a moderator assembly for an accelerator thermal neutron irradiation facility (ATNIF) for the treatment of superficial melanoma. The ATNIF moderator assembly consists of a 50-cm-high x 30-cm-diam cylinder of D2O, surrounded on its top and sides by a 40-cm-thick graphite reflector. This moderator assembly creates, at the surface of a large phantom at its irradiation port, a boron absorbed dose rate of (3.2 ± 0.2) cGy/(min·mA), for a tumor 10B concentration of 24 μg of 10B per gram of tissue. For a single-session dose equivalent of 40 Sv to the tumor, the treatment times is 13 min for a 30-mA proton beam. With different moderator assemblies, a 30-mA, 2.5-MeV proton accelerator can be used to treat both superficial and deep lesions from melanomas and gliomas