Measurements of Lineal Energy Spectra for Neutron Capture Therapy Using a Boron Doped Let Chamber

Abstract

Preclinical studies for boron neutron capture therapy (BNCT) using epithermal neutrons are ongoing at several laboratories. The absorbed dose in tumor cells depends on the boron concentration, thermal neutron flux at depth, size of the cell, plus fast neutron and gamma contamination in the epithermal beam. Monte Carlo computer simulations can estimate the various dose components, but dosimetry and treatment planning for BNCT present unique difficulties. Dosimetry is complicated by the admixture of thermal, epithermal, and fast neutrons, plus gamma rays; and the array of secondary high linear energy transfer (LET) particles produced within the patient from neutron interactions. Absorbed dose and radiation quality will be difficult to determine, and microdosimetry may be a viable technique for determining these quantities. Only one set of microdosimetric data for BNCT has previously been reportedl. Spectra were measured in air for an epithermal beam, using a tissue equivalent (TE) proportional counter to assess the effects of beam filter designs. We report here the first set of in phantom microdosimetric measurements using paired TE and TE+boron chambers on an epithermal beam. Such measurements permit assessment of the dose enhancement factor, and lineal energy distributions of the boron capture reaction.