Towards in vivo monitoring of neutron distributions for quality control of BNCT

In BNCT, local boron concentration, thermal neutron distribution and patient positioning largely determine this dose. In vivo measurements of these factors would considerably improve quality control and safety. Hydrogen gamma-rays emitted by the patient during therapy can serve as a measure of the thermal neutron distribution over the irradiated volume. They can be measured with spatial resolution by means of a scanning gamma-ray telescope. Measurements were compared with calculations with the treatment planning program (rtt_MC) and with MCNP. Measurements on several phantoms gave excellent agreement with calculations of the thermal neutron distribution. For patients, however, differences up to 20%2were observed. The patient measurements were reproducible between irradiation fractions.