We investigated the basic thermoluminescence (TL) characteristics of Cr-doped low-meltingpoint Al 2 O 3 . The concentration of Cr 2 O 3 in this study ranged from 0.01 to 1.0 wt%. Owing to the stabilization of the trapped state caused by Cr doping, we successfully improved the lowmelting-point Al 2 O 3 fading property dramatically. Then, the sensitivity of 0.05 wt% Cr-doped Al 2 O 3 to X-rays was about 4.8 times higher than that of the nondoped Al 2 O 3 , allowing the Al 2 O 3 to maintain its attractive properties to X-rays. Furthermore, the 0.05 wt% Cr-doped Al 2 O 3 had good properties for dosimetry owing to its high TL sensitivity, high reproducibility, high radiation resistivity, and high thermal stability in two dimensions. Finally, we demonstrated two-dimensional (2D) verifications of radiotherapy (RT) plans using Cr-doped Al 2 O 3 ceramic plates. The results had good agreement with RT plans.

In this study, the feasibility of using a thermoluminescent slab dosimeter (TLSD) in postal dosimetry audit for radiotherapy systems is examined. First, changes in material structure are evaluated by measuring changes in TLSD weight and temperature after heating and cooling. Then, a fading correction factor is derived by measuring the relationship between the elapsed time after irradiation and thermoluminescence (TL) intensity. Finally, the uncertainty in the absorbed dosimetry using the TLSD with the TL absorbed dose correction factor is evaluated. It is shown that the TLSD weight and heat flow change after heating. These changes are reversible upon cooling. Therefore, the material structure of the TLSD does not change after heating. The fading effect for the TLSD can be minimized by setting the elapsed time to more than 100 h. Furthermore, measurement accuracy can be improved by correcting the fading. The overall measurement uncertainty or expanded relative standard uncertainty for this measurement method is 1.80%. The TLSD has high material stability and measurement accuracy under a certain condition equivalent to that of conventional postal dosimetry audit conducted using a glass dosimeter. The TLSD can be used as a 2D measurement device for postal dosimetry audit.

Despite their advantages, two-dimensional (2D) thermoluminescence dosimeters (TLDs) have not yet replaced film dosimeters owing to their nonuniformity and low repeatability. A 2D TLD based on Al 2 O 3 :Cr ceramics is a promising new reusable passive dosimeter. 2D Al 2 O 3 :Cr TLDs can be used for geometry check tests and dose distribution verification in robotic radiosurgery using monoenergetic X-ray beams. In this work, the dependence of energy on the field size and water depth of 2D Al 2 O 3 :Cr TLDs for 4, 6, and 10 MV X-ray beams was investigated, because multienergy X-ray beams are used in radiotherapy. Intensity-modulated radiotherapy plan verifications were performed using the TLDs. The TLDs were found to have a large field size dependence for each energy, but their water depth dependence was small at a water depth above 4 cm for each energy. The relative dose distributions were verified with high accuracy using the TLDs.

In the neutron irradiation field in boron neutron capture therapy, neutron rays and γ-rays are mixed, and it is not easy to selectively measure only neutron rays. The currently used gold activation method is expensive and not suitable for measuring the dose distribution with high spatial resolution. Therefore, there is increasing demand for a simple neutron measurement method for periodic inspections and treatment planning in boron neutron capture therapy (BNCT). Cd has a large nuclear reaction cross section solely for thermal neutrons, and converts thermal neutrons to γ-rays by the (n, γ) reaction. Therefore, in this study, we investigated a method for calculating the thermal neutron fluence by installing Cd as a neutron converter on Cr-doped Al 2 O 3 (Al 2 O 3 :Cr), which is a thermoluminescence dosimeter, and measuring the converted γ-ray dose with the Al 2 O 3 :Cr. After a 30 min irradiation experiment using the Kyoto University research reactor, the amount of thermoluminescence (TL) increased 101-fold after installing a Cd converter compared with the case of no Cd converter. In addition, the dependence of the TL response on the irradiation time showed excellent proportionality, suggesting the possibility of selectively measuring only the thermal neutron fluence.

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