Sensitivity of a bone-equivalent polymer gel dosimeter for measuring the dose to bone during radiation therapy.

Treatment planning systems that use the Monte Carlo algorithm can calculate the dose to the medium (Dm) in non-water-equivalent tissues such as bones. However, Dm cannot be verified using actual measurements; therefore, it is necessary to develop tissue-equivalent dosimeters. In this study, we developed a bone-equivalent polymer gel dosimeter (BPGD) that can measure the dose absorbed by the bone and investigated its sensitivity. The BPGDs were prepared by adding 3.0 mol of calcium hydrogen phosphate dihydrate as a component of bone to an improved dose-sensitive polyacrylamide gelatin and tetrakis hydroxymethyl phosphonium chloride (iPAGAT). One day after preparation, the BPGDs were irradiated with a field size of 15 × 15 cm2 using a 10 MV X-ray beam to evaluate the dose sensitivity, dose-rate dependence, and dose-integration dependence. One day after dose exposure, the BPGDs were scanned using a 0.4 T MRI APERTO Eterna (Hitachi, Tokyo, Japan) to obtain R2 values. The difference between the R2 values of 6 Gy and 0 Gy was up to 5 s-1, and the R2 curve plateaued in the high-dose region. Moreover, the BPGD did not depend on the integration of the dose and dose rates. Therefore, the BPGDs that we developed can determine the radiation dose to bones.

Interaction of human MCM2-7 proteins with TIM, TIPIN and Rb.

Interactions of human MCM2-7 proteins with the proteins of TIM, TIPIN, an amino-terminal fragment of Rb, and p27 were examined by co-immuno-precipitation experiment using cell lysates of co-expressed insect cells. TIM and TIPIN, both of which are involved in regulation of DNA replication fork progression, mainly interacted with MCM3-7 proteins. The amino-terminal fragment of Rb, which inhibits DNA replication in Xenopus egg extracts, was able to bind with MCM3 and MCM6 proteins in addition to MCM7 protein. In contrast, p27 was not able to bind any MCM2-7 proteins under the comparable conditions. These results indicate that the proteins, which are known to interact with MCM proteins, bind with MCM2-7 proteins with different affinities and specificities.