Specification of the physical and biologically effective absorbed dose in radiation therapies utilizing the boron neutron capture reaction

Abstract

This thesis addresses issues concerning the dosimetry of BNCT, offering a method to more accurately obtain the absorbed dose and a framework for predicting its biological effectiveness. A dual miniature tissue‐equivalent proportional counter (TEPC) technique is introduced as a tool for microdosimetry of BNCT. These paired A‐150 and TEPCs with 12.3 mm3 collecting volumes allow measurements in high flux fields and provide excellent spatial resolution. Single event charged particle spectra measured using these TEPCs allow accurate dose component separation in mixed fields as well as an assessment of the radiation quality. Measurements in epithermal neutron beams used for the current clinical trials for BNCT at the Brookhaven National Laboratory and the Massachusetts Institute of Technology are provided. These data represent an intercomparison of the radiation quality and beam characteristics of these two BNCT facilities using a single phantom and measurement technique. Photon and neutron absorbed doses measured using TEPC microdosimetry agree with results from conventional methods. However, TEPC measured BNC doses conflict with those calculated from foil activation measurements. This thesis also investigates the potential enhancement of fast neutron therapy using the BNC reaction. Methods for modification of a fast neutron therapy beam to increase the BNC enhancement are reviewed. Results of these feasibility studies are encouraging, indicating the possibility of therapeutic gains greater than 30% over conventional fast neutron therapy at depths required to treat brain lesions. An ionization chamber‐based system designed for BNC dosimetry of the modified fast neutron beam is also introduced. The advantages of this ionization chamber technique and TEPC microdosimetry technique over conventional methods are reviewed, elucidating the utility of these dosimetry systems for neutron capture therapy.