γ-Ray measurements in boron neutron capture therapy using BeO ceramic thermoluminescence dosimeter

In boron neutron capture therapy (BNCT), neutrons and γ-rays cause different biological effects, and it is necessary to discriminate between them for treatment planning and periodic inspections. Currently, the BeO powder thermoluminescence dosimeter (BeO powder TLD) is used for γ-ray dosimetry in mixed neutron and γ-ray fields due to the small capture cross section for neutrons, but correction is required because of the effects of neutron-induced activation. Besides, sales of BeO powder TLDs have been discontinued because the highly toxic BeO is readily dispersed when the detector is damaged. Therefore, the development of alternative replacement technologies for BeO powder TLDs that are not affected by neutrons is an important issue. In this study, we investigated the measurement of the γ-ray dose during BNCT using a BeO ceramic TLD, whereby the BeO was not released into the air. After 5, 15, 30, and 60 min of irradiation using the Kyoto University Research Reactor, the amount of thermoluminescence (TL) from the BeO ceramic TLD was shown to increase with irradiation time. In addition, the γ-ray dose, which was derived by converting the amount of TL to the dose, showed excellent proportionality to the irradiation time and was found to be comparable to the γ-ray dose measured with a BeO powder TLD. These results demonstrated that the BeO ceramic TLD can selectively measure only the γ-ray dose without influence by neutrons. Thus, our approach represents a new γ-ray dose measurement strategy that does not require correction for the contribution from thermal neutrons.