Microdosimetric Analysis of Absorbed Dose in Boron Neutron Capture Therapy

Abstract

The biological effectiveness of absorbed dose in BNCT depends on relative contributions from the gamma, neutron and the thermal neutron capture dose components, and on the resulting spectrum of secondary charged particles. This spectrum is a variable, likely to change within the patient, with subcellular boron location, and between different beams. In the present work, a dual proportional counter microdosimetric technique to measure and analyse the absorbed dose and its single event spectrum is described. Single event spectra of the gamma, neutron and 10B dose components have been separately calculated from experimental measurements. Spectra for a 6 µm diameter volume (simulating a cell nucleus), with a uniform distribution of 10B and with 10B localised external to it have been calculated. For the same macroscopic 10B dose, the dose to the nucleus with the 10B localised outside the nucleus is reduced to half of that when it is uniformly distributed. The reduced dose is of a lower average lineal energy compared to the uniform dose; its relative effectiveness depends on the radiosensitivity of the irradiated tissue, being larger for sensitive tissues and smaller for radioresistant tissues.