用于 HDR Ir 近距离放射治疗源的辐射光致发光玻璃剂量计的能量依赖性。

Department of Radiation Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo, 113-8677, Japan.

Department of Radiation Oncology, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi, 980-8574, Japan.

Med Phys. 2019 Feb;46(2):964-972. doi: 10.1002/mp.13319. Epub 2018 Dec 26.

PURPOSE

We determined correction factors for absorbed dose energy dependence and intrinsic energy dependence for measurements of absorbed dose to water around an Ir source using a radiophotoluminescent glass dosimeter (RPLD) calibrated with a 4-MV photon beam.

METHODS

The ratio of the absorbed dose to the water and the average absorbed dose to RPLD for the Ir beam relative to the same ratio in a 4 MV photon beam defines the absorbed dose energy dependence and was determined at distances of 2-10 cm (at intervals of 1 cm) from the Ir source in a water phantom using the egs_chamber user code. The RPLD was calibrated to measure absorbed dose to water, D , in a 4 MV photon beam using an ionization chamber, which was also used to measure absorbed dose to water, D , in a water phantom using the Ir source. The detector response radiophotoluminescence (RPL signal per average absorbed dose in the detector) in the Ir beam relative to that in the 4 MV photon beam (the relative intrinsic efficiency) was determined experimentally. Finally, the beam quality correction factor was obtained as the quotient between the absorbed dose energy dependence and the relative intrinsic efficiency and corrects for the difference between the beam quality Q used at calibration and the beam quality Q used in the measurements.

RESULTS

The relative dose ratio of the average absorbed dose to water relative to RPLD ranged from 0.930 to 0.746, and the beam quality correction factor ranged from 0.999 to 0.794 for distances of 2-10 cm from the Ir source. The relative detector response to an Ir source and a 4-MV photon beam was 0.930, and it did not vary significantly with distance.

CONCLUSIONS

These results demonstrate that corrections for absorbed dose energy dependence and intrinsic energy dependence are required when using an RPLD to measure with sources different from the reference source providing the primary calibration.

目的

我们使用经 4-MV 光子束校准的辐射光致发光玻璃剂量计（RPLD），测定 Ir 源周围水的吸收剂量，确定吸收剂量能量依赖性和固有能量依赖性的校正因子。

方法

在水模体中，从 Ir 源 2-10cm 处（间隔 1cm），使用 egs_chamber 用户代码，测定 Ir 束相对于 4-MV 光子束的水吸收剂量比（Dw）和 RPLD 平均吸收剂量比，确定吸收剂量能量依赖性。RPLD 经校准，可在 4-MV 光子束中测量水吸收剂量 Dw，使用电离室也可在水模体中测量 Ir 源的水吸收剂量 Dw。在 Ir 束中，探测器响应光致发光（RPL 信号与探测器中平均吸收剂量的比值）相对于 4-MV 光子束的比值（相对固有效率）通过实验确定。最后，将吸收剂量能量依赖性与相对固有效率相除，得到束质校正因子，该因子校正了校准和测量时使用的束质 Q 之间的差异。