Tanaka Kenichi, Kajimoto Tsuyoshi, Hayashi Takahiro, Asanuma Osamu, Hori Masakazu, Kamo Ken-Ichi, Sumida Iori, Takahashi Yutaka, Tateoka Kunihiko, Bengua Gerard, Sakata Koh-Ichi, Endo Satoru
Quantum Energy Applications, Graduate School of Engineering, Hiroshima University, 1-4-1, Kagamiyama, Higashi-Hiroshima, Hiroshima, Japan.
Division of Radiology and Nuclear Medicine, Sapporo Medical University Hospital, South 1, West 17, Chuo-ward, Sapporo, Hokkaido, Japan.
J Radiat Res. 2018 Jul 1;59(4):484-489. doi: 10.1093/jrr/rry021.
This study aims to demonstrate the feasibility of a method for estimating the strength of a moving brachytherapy source during implantation in a patient. Experiments were performed under the same conditions as in the actual treatment, except for one point that the source was not implanted into a patient. The brachytherapy source selected for this study was 125I with an air kerma strength of 0.332 U (μGym2h-1), and the detector used was a plastic scintillator with dimensions of 10 cm × 5 cm × 5 cm. A calibration factor to convert the counting rate of the detector to the source strength was measured and then the accuracy of the proposed method was investigated for a manually driven source. The accuracy was found to be under 10% when the shielding effect of additional needles for implantation at other positions was corrected, and about 30% when the shielding was not corrected. Even without shielding correction, the proposed method can detect dead/dropped source, implantation of a source with the wrong strength, and a mistake in the number of the sources implanted. Furthermore, when the correction was applied, the achieved accuracy came close to within 7% required to find the Oncoseed 6711 (125I seed with unintended strength among the commercially supplied values of 0.392, 0.462 and 0.533 U).
本研究旨在证明一种在患者体内植入近距离放射治疗源时估算其强度的方法的可行性。实验在与实际治疗相同的条件下进行，唯一不同的是源未植入患者体内。本研究选用的近距离放射治疗源为空气比释动能强度为0.332 U（μGym²h⁻¹）的¹²⁵I，所用探测器为尺寸为10 cm×5 cm×5 cm的塑料闪烁体。测量了将探测器计数率转换为源强度的校准因子，然后针对手动驱动源研究了所提方法的准确性。当对其他位置植入的附加针的屏蔽效应进行校正时，发现准确性在10%以内；未进行屏蔽校正时，准确性约为30%。即使不进行屏蔽校正，所提方法也能检测到源失效/掉落、植入强度错误的源以及植入源数量错误。此外，应用校正后，所达到的准确性接近找到Oncoseed 6711（在商业供应值0.392、0.462和0.533 U中强度意外的¹²⁵I种子）所需的7%以内。
