Marchese M J, Goldhagen P E, Zaider M, Brenner D J, Hall E J
Department of Radiation Oncology, College of Physicians and Surgeons of Columbia University, New York, NY 10032.
Int J Radiat Oncol Biol Phys. 1990 Jun;18(6):1407-13. doi: 10.1016/0360-3016(90)90315-b.
The relative biological effectiveness (RBE) of photon radiation from encapsulated Iodine-125 "seed" sources has not previously been investigated in human cells. The RBE of 125I photons relative to 137Cs gamma rays was examined in normal diploid human fibroblasts derived from lung and skin. The cells were irradiated in plateau phase using a specially designed incubator-irradiator which permitted simultaneous 125I and 137Cs irradiation. The cells were irradiated at various dose rates ranging from 7 to 70 cGy/hr. Dosimetry was performed using Monte Carlo computer calculations to simulate the 125I irradiations and the exposure-standardization measurements made by the U.S. National Bureau of Standards which are the basis for the specified strengths of 125I seeds. Simulation of the exposure standardization measurements revealed systematic errors due to the unrecognized presence of low-energy fluorescence X rays. The specified activity of the type of seeds used for this study (high-activity, no radiographic marker) was found to be too high by more than 10%. The RBE of 125I assessed with both lung fibroblast lines was found to be 1.2 and was 1.3 for the skin fibroblasts. The RBE did not change over the range of dose rates tested. In fact, for both 125I and 137Cs, the dose response curves did not change with dose rate over the range tested, implying full repair of sublethal damage at dose rates below 70 cGy/hr in these non-dividing cells.
此前尚未在人体细胞中研究过封装的碘 - 125“种子”源发出的光子辐射的相对生物有效性（RBE）。在源自肺和皮肤的正常二倍体人成纤维细胞中检测了125I光子相对于137Csγ射线的RBE。使用专门设计的培养箱 - 辐照器在平台期对细胞进行辐照，该辐照器允许同时进行125I和137Cs辐照。细胞在7至70 cGy/小时的各种剂量率下进行辐照。使用蒙特卡罗计算机计算进行剂量测定，以模拟125I辐照以及美国国家标准局进行的曝光标准化测量，这些测量是125I种子指定强度的基础。对曝光标准化测量的模拟揭示了由于未识别的低能荧光X射线的存在而导致的系统误差。发现本研究使用的种子类型（高活性，无射线照相标记）的指定活度高出10％以上。用两种肺成纤维细胞系评估的125I的RBE为1.2，皮肤成纤维细胞的RBE为1.3。在所测试的剂量率范围内，RBE没有变化。事实上，对于125I和137Cs，在测试范围内剂量响应曲线均不随剂量率变化，这意味着在这些非分裂细胞中，剂量率低于70 cGy/小时时亚致死损伤得到完全修复。
