Scatter and energy dependence of thermoluminescent dosimeter to determine half-value layer in digital mammography: Monte Carlo results

The aim of this study was to investigate the responses of thermoluminescent dosimeters (TLDs) within a TLD accommodation device, which was designed for half-value layer (HVL) determinations, using a Monte Carlo method. In a previous study, HVL measurements using TLDs exhibited extremely poor accuracies, about 50% uncertainty. A compact device that accommodated 15 TLD chips and 4 different thicknesses of aluminum sheets in a small holder was designed to determine HVLs for mammographic exposure conditions. The scatter and energy dependence correction factors must be taken into account when using this device. In this study, the scatter correction factor was separated into two components: scatter from an acrylic holder and scatter from covering aluminum sheets. The absolute energy dependence correction factor of TLDs was also evaluated. Scatter from the acrylic holder ranged from 2.5% to 2.9% and was independent of column positions. The influence of scatter and energy dependence increased with aluminum sheet thickness due to beam qualities. The designed TLD accommodation device was useful for determining HVLs in a single exposure when the scatter correction factors for the device and energy dependence correction factors for TLDs were taken into consideration.