A new monitoring system for the thermal neutron fluence rate and gamma dose rate in boron neutron capture therapy

A new monitoring system for the thermal neutron fluence rate and gamma dose rate is described for boron neutron capture therapy (BNCT). A small pn junction Si diode was used as a new detector which was mechanically stronger and had better stability than a surface barrier detector. The pulse height of signals due to thermal neutrons was sufficiently high and was separated from signals due to gamma rays. The radiation damage to the detectors which results in a reduction of the pulse height was found to be quite small. By using the detectors, the thermal neutron fluence rate and gamma dose rate, not only in the head but also in the body, were measured simultaneously during therapy, and the new system has been efficiently used for BNCT of brain tumours. (author)