DETERMINATION OF THE ~(10)B DOSE IN BNCT USING LiF-TLD

摘要

The ~(10)B dose in boron neutron capture therapy (BNCT) was usually determined by multiplying the thermal neutron flux by the ~(10)B concentration and the dose conversion factor. In this kind of application, the thermal neutron flux was commonly measured using gold foil activation techniques with and without the cadmium cover, assuming that the neutron spectrum has a Maxwellian distribution in the thermal range. This always generated uncertainties because the thermal neutron energy spectrum has no Maxwellian distribution in the body. The potential to determine the ~(10)B dose by using a single LiF thermoluminescent dosimeter (TLD) is studied.rnThe ~(10)B dose in BNCT derives from the reaction of the thermal neutron with the ~(10)B element. It always dominates the irradiation dose if the ~(10)B concentration is higher than 20 ppm. Since the trends of the ~(10)B absorption cross sections are similar to ~6Li in the thermal neu-rntron range, the LiF-TLD can be used for ~(10)B dose determination in BNCT if the reaction of the thermal neutron with ~6Li dominates the TLD response. The MCNP code is used to simulate the energy deposition in various LiF-TLD s and to show the suitability of LiF-TLD used for ~(10)B dose determination in BNCT.rnThe preliminary MCNP simulation shows that the TLD response strongly depends on the ~6LiF content in the TLD. Comparing the TLD response, the ~(10)B reaction, and the thermal neutron flux, they show the same distribution as a function of depth in a phantom irradiated with the BNCT neutron. On the other hand, not only is there a thermal neutron flux depression due to self-shielding within the TLD chip, but also there is significant perturbation around the TLD if the ~6LiF content in the TLD is high enough. To balance these two factors, TLD-100 was recommended as a ~(10)B dosimeter for BNCT.