Tanaka Kenichi, Endo Satoru, Tateoka Kunihiko, Asanuma Osamu, Hori Masakazu, Takagi Masaru, Bengua Gerard, Kamo Ken-Ichi, Sato Kaori, Takeda Hiromitsu, Hareyama Masato, Sakata Koh-Ichi, Takada Jun
Department of Medicine, Graduate School of Sapporo Medical University, South 1, West 16, Chuo-ward, Sapporo Hokkaido 060-8543, Japan
Quantum Energy Applications, Graduate School of Engineering, Hiroshima University, 1-4-1, Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan.
J Radiat Res. 2014 Nov;55(6):1146-52. doi: 10.1093/jrr/rru058. Epub 2014 Jul 1.
This study sought to demonstrate the feasibility of estimating the source strength during implantation in brachytherapy. The requirement for measuring the strengths of the linked sources was investigated. The utilized sources were (125)I with air kerma strengths of 8.38-8.63 U (μGy m(2) h(-1)). Measurements were performed with a plastic scintillator (80 mm × 50 mm × 20 mm in thickness). For a source-to-source distance of 10.5 mm and at source speeds of up to 200 mm s(-1), a counting time of 10 ms and a detector-to-needle distance of 5 mm were found to be the appropriate measurement conditions. The combined standard uncertainty (CSU) with the coverage factor of 1 (k = 1) was ∼15% when using a grid to decrease the interference by the neighboring sources. Without the grid, the CSU (k = 1) was ∼5%, and an 8% overestimation due to the neighboring sources was found to potentially cause additional uncertainty. In order to improve the accuracy in estimating source strength, it is recommended that the measurment conditions should be optimized by considering the tradeoff between the overestimation due to the neighboring sources and the intensity of the measured value, which influences the random error.
本研究旨在证明近距离放射治疗植入过程中估算源强的可行性。研究了测量相关源强的要求。所使用的源为空气比释动能强度为8.38 - 8.63 U（μGy m² h⁻¹）的¹²⁵I。测量使用了厚度为80 mm×50 mm×20 mm的塑料闪烁体。对于源到源距离为10.5 mm且源速度高达200 mm s⁻¹的情况，发现计数时间为10 ms且探测器到针的距离为5 mm是合适的测量条件。使用网格减少相邻源的干扰时，包含因子为1（k = 1）的合成标准不确定度（CSU）约为15%。不使用网格时，CSU（k = 1）约为5%，并且发现由于相邻源导致的8%高估可能会引起额外的不确定度。为了提高源强估算的准确性，建议通过考虑相邻源导致的高估与影响随机误差的测量值强度之间的权衡来优化测量条件。
