Determination and optimization of radition quality of calibration system for mammography dosimeters in IAEA/WHO secondary standard dosimetry laboratory
10.3760/cma.j.issn.0254-5098.2021.10.009
- VernacularTitle:次级标准剂量学实验室乳腺低能X射线剂量仪校准系统线质测定与优化研究
- Author:
Xipeng ZHAO
1
;
Baorong YUE
;
Hui XU
Author Information
1. 中国疾病预防控制中心辐射防护与核安全医学所 辐射防护与核应急中国疾病预防控制中心重点实验室，北京 100088
- Keywords:
Calibration system for mammography dosimeters;
Tube voltage;
HVL 1;
Aluminum sheet thickness
- From:
Chinese Journal of Radiological Medicine and Protection
2021;41(10):772-777
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To determine and optimize the radiation quality of the calibration system for mammography dosimeters in IAEA/WHO Secondary Standard Dosimetry Laboratory and to study the requirements for accuracy of thickness of the aluminum sheets used in the measurement, with a view to ensure the accuracy of the radiation quality.Methods:For the measurements of tube voltage and RQR-M radiation quality, a standard kV meter was used to determine the actual tube voltage value of the system under continuous exposure for 30 s by setting tube voltage of 25, 28, 30 and 35 kV, respectively, and aluminum sheet method was used to determine the first half value layer (HVL 1). The kV values were adjusted to make the reading of the standard kV meter as close as possible to its nominal value, so as to obtain the set kV value, actual tube voltage and HVL 1 per 1 kV within the nominal 25-35 kV range. For effects of different thickness of aluminum sheets on the result of HVL 1 measurement, a comparison was made between HVL 1 measured by aluminum sheet with thickness of 0.318 mm and 0.369 mm and HVL 1 measured under 18 different groups of aluminum sheet using a selected 30 kV tube voltage. Results:After the set kV values were adjusted, the actual tube voltage deviations from the nominal values under 25, 28, 30 and 35 kV were reduced from 0.55, 0.34, 0.33, 0.30 to 0.04, 0.02, -0.04, -0.01, and the HVL 1 deviations were reduced from 0.011, 0.007, 0.010, 0.012 to 0.000, 0.003, 0.003, 0.010, respectively. When the thickness differences between the two types of aluminum sheet and the reference HVL 1 were both within 0.1 mm, the deviations of the measured HVL 1 were all less than 0.01 mm Al, and the result was relatively accurate. However, when the differences exceeded that of 0.1 mm, most of the deviations of the measured HVL 1 were between 0.01 and 0.02 mm Al, and the measured result was not accurate. Conclusions:Although the RQR-M radiation quality of the calibration system was deviated, it is still within the range specified under the IEC 61267-2005. The radiation quality was closer to the standard values after fine-tuning the system tube voltage. In order to measure the HVL 1 more accurately, the thickness differences between the used aluminum sheet and nominal HVL 1 should not be greater than 0.1 mm Al.
