Set-up and calibration of a method to measure 10B concentrationin biological samples by neutron autoradiography

A selective uptake of boron in the tumor is the base of Boron Neutron Capture Therapy, which can destroy the tumor substantially sparing the normal tissue. In order to deliver a lethal dose to the tumor, keeping the dose absorbed by normal tissues below the tolerance level, it is mandatory to know the 10B concen- tration present in each kind of tissue at the moment of irradiation. This work presents the calibration pro- cedure adopted for a boron concentration measurement method based on neutron autoradiography, where biological samples are deposited on sensitive films and irradiated in the thermal column of the TRIGA reactor (University of Pavia). The latent tracks produced in the film by the charged particles com- ing from the neutron capture in 10B are made visible by a proper etching, allowing the measurement of the track density. A calibration procedure with standard samples provides curves of track density as a function of boron concentration, to be used in the measurement of biological samples. In this paper, the bulk etch rate parameter and the calibration curves obtained for both liquid samples and biological tissues with known boron concentration are presented. A bulk etch rate value of (1.64 ± 0.02)microns/h and a linear dependence with etching time were found. The plots representing the track density versus the boron concentration in a range between 5 and 50 lg/g (ppm) are linear, with an angular coefficient of (1.614 ± 0.169)x10^-3 tracks/(lm2 ppm) for liquids and (1.598 ± 0.097)x10^-2 tracks/(lm2 ppm) for tissues.