Phantom Validation and Beam Line Characterization for Boron Neutron Capture Synovectomy Studies at McMaster University

Abstract

Rheumatoid arthritis is characterized by severe inflammation of the synovial tissue in the joint, which causes pain and degradation of the bone. The novel treatment boron neutron capture synovectomy (BNCS) utilizes the 10B(n,a)7Li nuclear reaction to ablate the synovial tissue as an attempt to control these effects. The typical procedure involves intra-articular injection of a boronated compound followed by irradiation of the joint with a thermalized neutron beam. An anthropomorphic knee phantom has been designed and manufactured in a manner to display similar moderating and reactive properties to human soft tissue and bone. The intended use of such a phantom is the determination of RBE values of boron compounds on several human cell types. Beam line characterization has been performed on the 3 MV KN single-ended accelerator at McMaster University using MCNP5. Testing was accomplished for neutron spectra produced by 2.00, 2.15, and 2.25 MeV protons on a thick lithium target. The maximum thermal flux through the interior cavity of the phantom was attained for moderator thicknesses of 3.25, 3.25, and 3.5 cm of high-density polyethylene (HDPE) at 2.00, 2.15, and 2.25 MeV, respectively, via MCNP5 for a phantom position 45° relative to the incident proton beam. Experimentally determined thermal flux maxima occurred using 1.75, 1.75 and 2.0 cm of HDPE for the corresponding energies. Causes for discrepancies were cited as phantom material inconsistencies, as well as possible errors in the analytical compilation of the MCNP5 source cards for the 7Li(p,n)7Be reaction. Experimentally, selecting a proton energy of 2.25 MeV showed little advantageous characteristics over 2.15 MeV. It is concluded that a Monte Carlo based code with charged particle transport capabilities may be desirable for further neutron dosimetry and standardized materials should be used whenever possible for manufacturing a “neutron phantom”.