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Boron neutron capture therapy for the treatment of cerebral gliomas. I: Theoretical evaluation of the efficacy of various neutron beams
Author(s) -
Zamenhof Robert G.,
Murray Brian W.,
Brownell Gordon L.,
Wellum Glyn R.,
Tolpin Eugene I.
Publication year - 1975
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.594168
Subject(s) - neutron capture , neutron , neutron temperature , materials science , imaging phantom , boron , beam (structure) , neutron radiation , relative biological effectiveness , neutron source , radiochemistry , nuclear medicine , irradiation , nuclear physics , chemistry , physics , optics , medicine
The technique of boron neutron capture therapy in the treatment of cerebral gliomas depends upon the selective loading of the tumor with a 10 B‐enriched compound and subsequent irradiation of the brain with low‐energy neutrons. The charged particles produced in the 10 B ( n ,α) 7 Li reaction have ranges in tissue of less than 10 μm so that the dose distribution closely follows the 10 B distribution even to the cellular level. The effectiveness of this therapy procedure is dependent not only on the 10 B compound but on the spectral characteristics of the neutron source as well. Hence, an optimization of these characteristics will increase the chances of therapeutic success. Transport calculations using a neutral particle transport code have been made to determine the dose–depth distributions within a simple head phantom for five different incident neutron beams. Comparison of these beams to determine their relative therapeutic efficacy was made by the use of a maximum useable depth criterion. In particular, with presently available compounds, the MIT reactor (MITR) therapy beam (a) is not inferior to a pure thermal neutron beam, (b) would be marginally improved if its gamma‐ray contamination were eliminated, (c) is superior to a partially 10 B‐filtered MITR beam, and (d) produces a maximum useable depth which is strongly dependent upon the tumor‐to‐blood ratio of 10 B concentrations and weakly dependent upon the absolute 10 B concentration in tumor. A pure epithermal neutron beam with a mean energy of 37 eV is shown to have close to the optimal characteristics for boron neutron capture therapy. Furthermore, these optimal characteristics can be approximated by a judiciously D 2 O moderated and 10 B‐filtered 252 Cf neutron source. This tailored 252 Cf source would have at least a 1.5 cm greater maximum useable depth than the MITR therapy beam for realistic 10 B concentrations. However, at least one gram of 252 Cf would be needed to make this a practical therapy source. If the moderated 252 Cf source is not 10 B filtered, the resultant neutron beam has characteristics similar to those of the MITR beam with no gamma‐ray contamination. For such a beam, 100 mg of 252 Cf would produce a flux of 2.4×10 8 neutrons/(cm 2 sec), which is an intensity suitable for therapy applications.