Mizuno Hideyuki, Fukumura Akifumi, Fukahori Mai, Sakata Suoh, Yamashita Wataru, Takase Nobuhiro, Yajima Kaori, Katayose Tetsurou, Abe-Sakama Kyoko, Kusano Yohsuke, Shimbo Munefumi, Kanai Tatsuaki
National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba-shi 263-8555, Japan.
Association for Nuclear Technology in Medicine, 7-16, Nihonbashikodenmacho, Chuou-ku, Tokyo 103-0001, Japan.
Med Phys. 2014 Nov;41(11):112104. doi: 10.1118/1.4898596.
The purpose of this study was to obtain a set of correction factors of the radiophotoluminescent glass dosimeter (RGD) output for field size changes and wedge insertions.
Several linear accelerators were used for irradiation of the RGDs. The field sizes were changed from 5 × 5 cm to 25 × 25 cm for 4, 6, 10, and 15 MV x-ray beams. The wedge angles were 15°, 30°, 45°, and 60°. In addition to physical wedge irradiation, nonphysical (dynamic/virtual) wedge irradiations were performed.
The obtained data were fitted with a single line for each energy, and correction factors were determined. Compared with ionization chamber outputs, the RGD outputs gradually increased with increasing field size, because of the higher RGD response to scattered low-energy photons. The output increase was about 1% per 10 cm increase in field size, with a slight difference dependent on the beam energy. For both physical and nonphysical wedged beam irradiation, there were no systematic trends in the RGD outputs, such as monotonic increase or decrease depending on the wedge angle change if the authors consider the uncertainty, which is approximately 0.6% for each set of measured points. Therefore, no correction factor was needed for all inserted wedges. Based on this work, postal dose audits using RGDs for the nonreference condition were initiated in 2010. The postal dose audit results between 2010 and 2012 were analyzed. The mean difference between the measured and stated doses was within 0.5% for all fields with field sizes between 5 × 5 cm and 25 × 25 cm and with wedge angles from 15° to 60°. The standard deviations (SDs) of the difference distribution were within the estimated uncertainty (1SD) except for the 25 × 25 cm field size data, which were not reliable because of poor statistics (n = 16).
A set of RGD output correction factors was determined for field size changes and wedge insertions. The results obtained from recent postal dose audits were analyzed, and the mean differences between the measured and stated doses were within 0.5% for every field size and wedge angle. The SDs of the distribution were within the estimated uncertainty, except for one condition that was not reliable because of poor statistics.
本研究的目的是获取一套针对射野大小变化和楔形板插入的放射性光致发光玻璃剂量计（RGD）输出的校正因子。
使用多台直线加速器对RGD进行照射。对于4、6、10和15 MV的X射线束，射野大小从5×5 cm变为2×5 cm。楔形角为15°、30°、45°和60°。除了物理楔形板照射外，还进行了非物理（动态/虚拟）楔形板照射。
对每个能量下获得的数据用一条直线进行拟合，并确定校正因子。与电离室输出相比，由于RGD对散射低能光子的响应较高，RGD输出随射野大小增加而逐渐增加。射野大小每增加10 cm，输出增加约1%，且因束流能量略有差异。对于物理和非物理楔形束照射，如果考虑不确定性（每组测量点约为0.6%），RGD输出没有系统趋势，如不随楔形角变化单调增加或减少。因此，对于所有插入的楔形板不需要校正因子。基于这项工作，2010年开始使用RGD进行非参考条件下的邮政剂量核查。分析了2010年至2012年的邮政剂量核查结果。对于射野大小在5×5 cm至25×25 cm之间且楔形角在15°至60°之间的所有射野，测量剂量与标称剂量之间的平均差异在0.5%以内。差异分布的标准差在估计的不确定性（1SD）范围内，但25×25 cm射野大小的数据除外，由于统计量较差（n = 16），该数据不可靠。
确定了一套针对射野大小变化和楔形板插入的RGD输出校正因子。分析了近期邮政剂量核查的结果，对于每个射野大小和楔形角，测量剂量与标称剂量之间的平均差异在0.5%以内。分布的标准差在估计的不确定性范围内，但有一个因统计量较差而不可靠的情况除外。
