Neutron dosimetry in boron neutron capture therapy using aqueous solutions of lithium acetate

This paper presents the development of a dosimetry method, based on liquid scintillation (LS) counting of the tritium that is produced in aqueous solutions of lithium acetate, for the determination of the boron and nitrogen absorbed doses in-phantom in BNCT. The dosimeter is passive, integrating, approximately tissue equivalent, and insensitive to gamma rays and the elastic scattering of fast neutrons. The dosimetry method exhibits a response which is proportional to the boron and nitrogen absorbed doses and which can be calibrated to NIST standard solutions of water spiked with tritium. For 0.2 g of lithium acetate dissolved in a milliliter of water, the measured sensitivity is (1.73±0.04)×10−9 cpm per unit of thermal neutron fluence (in neutrons/cm2). For the LS analyzer that was used, the background signal was 12.84±0.02 cpm, yielding a thermal neutron fluence threshold for this detection method of approximately 7×109 neutrons/cm2.