Determination of the 10B Dose in BNCT Using LiF-TLD

Abstract

The 10B dose in boron neutron capture therapy (BNCT) was usually determined by multiplying the thermal neutron flux by the 10B 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 10B dose by using a single LiF thermoluminescent dosimeter (TLD) is studied.The 10B dose in BNCT derives from the reaction of the thermal neutron with the 10B element. It always dominates the irradiation dose if the 10B concentration is higher than 20 ppm. Since the trends of the 10B absorption cross sections are similar to 6Li in the thermal neutron range, the LiF-TLD can be used for 10B 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-TLDs and to show the suitability of LiF-TLD used for 10B dose determination in BNCT.The preliminary MCNP simulation shows that the TLD response strongly depends on the 6LiF content in the TLD. Comparing the TLD response, the 10B 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 10B dosimeter for BNCT.