Boron neutron capture therapy for the treatment of cerebral gliomas. I: Theoretical evaluation of the efficacy of various neutron beams

Abstract

The technique of boron neutron capture therapy in the treatment of cerebral gliomas depends upon the selective loading of the tumor with a 10B-enriched compound and subsequent irradiation of the brain with low-energy neutrons. The charged particles produced in the 10B (n,alpha) 7Li reaction have ranges in tissue of less than 10 mum so that the dose distribution closely follows the 10B distribution even to the cellular level. The effectiveness of this therapy procedure is dependent not only on the 10B 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 10B-filtered MITR beam, and (d) produces a maximum useable depth which is strongly dependent upon the tumor-to-blood ratio of 10B concentrations and weakly dependent upon the absolute 10B 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. Futhermore, these optimal characteristics can be approximated by a judiciously D2O moderated and 10B-filtered 252Cf neutron source. This tailored 252Cf source would have at least a 1.5 cm greater maximum useable depth than the MITR therapy beam for realistic 10B concentrations. However, at least one gram of 252Cf would be needed to make this a practical therapy source. If the moderated 252Cf source is not 10B filtered, the resultant neutron beam has characteristics similar to those of the MITR beam with no gamma-ray contamination. For usch a beam, 100 mg of 252Cf would produce a flux of 2.4 X 10(8) neutrons/(cm2 sec), which is an intensity suitable for therapy applications.

Design of Epithermal Neutron Field Generated by 150-MeV Proton Beam Injections for Boron Neutron Capture Therapy

“…The CF values for normal tissue and tumors were fixed at 1.3 and 3.8 1) and the RBE n and RBE were selected as 3.2 and 1.0 1) , respectively. The D B value was calculated by the product of the neutron flux and the kerma coefficient proposed by Zamenhof et al 6) The D n and D were calculated using the neutron kerma coefficient for tissue and the photon mass energy absorption coefficient for tissue 7) . Because the neutron flux of System 2 is twice that of System 1, the therapeutic time for Systems 2 -4 is half that for System 1.…”

Boron Neutron Capture Therapy of Cerebral Gliomas

“…Calculations taking these and additional factors explicitly into account were made by Brownell et al (11) and have been reevaluated by us (76) and by Deutsch and Murray (18) in an attempt to define the radiation dose field more precisely. As a result, criteria for comparing the theoretically expected thera peutic efficacy of various combinations of neutron beam characteristics, tumor: blood boron concentration ratios, and tumor boron concentrations have been devised (76).…”

“…The considerations which apply to the calculation of the tumor dose and normal tissue dose for various tissue distributions of a boron-10 compound in the brain have recently been reviewed (18,76). In this paper we consider two methods for obtaining boron concentration distributions in glioma patients which would be adequate for clinical purposes.…”

Present Status of Boron Neutron Capture Therapy

“…Yet another alternative to create neutrons is by use of neutron-emitting radionuclides such as 2S2Cf (84,90) which has been used in some centres for treatment of cervical carinoma. One possibility for BNCT could be to find a tumour-specific boron compound (e.g.…”