Mixed field dosimetry of epithermal neutron beams for boron neutron capture therapy at the MITR‐II research reactor

Abstract

During the past several years, there has been growing interest in Boron Neutron Capture Therapy (BNCT) using epithermal neutron beams. The dosimetry of these beams is challenging. The incident beam is comprised mostly of epithermal neutrons, but there is some contamination from photons and fast neutrons. Within the patient, the neutron spectrum changes rapidly as the incident epithermal neutrons scatter and thermalize, and a photon field is generated from neutron capture in hydrogen. In this paper, a method to determine the doses from thermal and fast neutrons, photons, and the B-10(n, alpha)Li-7 reaction is presented. The photon and fast neutron doses are measured with ionization chambers, in realistic phantoms, using the dual chamber technique. The thermal neutron flux is measured with gold foils using the cadmium difference technique, the thermal neutron and B-10 doses are determined by the kerma factor method. Representative results are presented for a unilateral irradiation of the head. Sources of error in the method as applied to BNCT dosimetry, and the uncertainties in the calculated doses are discussed.

MAGIC polymer gel for dosimetric verification in boron neutron capture therapy

“…Current dosimeters include activation foils and wires, paired ionization chambers, and thermoluminescent dosimeters, all of which make mapping a 3D dose distribution laborious. ( 13 – 18 ) The properties of dosimetry gels make these substances suitable for determining 3D dose distributions in large and complex geometries. This approach is advantageous for BNCT: first, for beam dosimetry (experimentally verifying dose distribution in standard phantoms in three dimensions), and second, for verification of treatment planning in complex geometries such as the head and neck.…”

Accelerator‐based boron neutron capture therapy

“…The corresponding figures at E,=2.7 MeV are reported as 6 mb/steradian and 5 mb/steradian, respectively [12]. Another estimation is that the no contribution drops from 65% at E,=2.5 MeV, to 30% at 5 MeV, and 5% at 18 MeV [15]. At much higher energies (above 15 MeV), the low energy continuum dominates the spectrum [18] [19].…”

“…Since that time, many other measurements have been made at proton energies from threshold to 4.0 MeV. Table II-C-2 contains a list of these studies, as compiled by Byrd [15]. It is important to note that many of these measurements were undertaken to investigate the properties of a particular nuclear energy level.…”

“…Neutron spectra in head phantom resulting from the reaction 9 Be(d.n) E = 2.6 MeV and used in the calibration [15]. This initial step provides the exposure calibration constant in units of R/C.…”

“…For elderly patients (age > 60), the median survival drops to 6 months [14]. Despite advances in treatment techniques, the prognosis of these patients is not improving [15], and as a result, treatment is generally palliative and not curative [13] [1].…”