Wayne State University, Detroit, Michigan 48201-2013, USA.
Radiat Res. 2010 Mar;173(3):290-7. doi: 10.1667/RR1782.1.
Electronic brachytherapy systems are being developed that can deliver X rays of varying energy depending on the material of a secondary target. A copper target produces characteristic 8 keV X rays. Our aim was to determine whether 8 keV X rays might deliver greater biological effectiveness than megavoltage photons. Cells of the U251 human glioma cell line were used to compare the biological effects of 8 keV X rays and (60)Co gamma rays in terms of relative biological effectiveness (RBE), oxygen enhancement ratio (OER), and DNA damage. The RBE at 50% and 10% survival was 2.6 and 1.9, respectively. At 50% survival, the OER for cells treated with 8 keV X rays was 1.6 compared with 3.0 for (60)Co gamma rays. The numbers of H2AX foci per Gy after treatment with 8 keV X rays and (60)Co gamma rays were similar; however, the size of the foci generated at 8 keV was significantly larger, possibly indicating more complex DNA damage. The mean area of H2AX foci generated by 8 keV X rays was 0.785 microm(2) (95% CI: 0.756-0.814) compared with 0.491 microm(2) (95% CI: 0.462-0.520) for (60)Co gamma rays (P < 0.0001). Characteristic 8 keV X rays produce two to three times the biological effectiveness of megavoltage photons, with a radiobiological profile similar to higher-LET radiations.
正在开发能够根据次级靶材的材料提供不同能量 X 射线的电子近距离放疗系统。铜靶可产生特征性的 8keV X 射线。我们的目的是确定 8keV X 射线是否比兆伏光子具有更高的生物学效应。使用 U251 人胶质瘤细胞系的细胞，比较 8keV X 射线和（60）Co 伽马射线在相对生物学效应（RBE）、氧增强比（OER）和 DNA 损伤方面的生物学效应。50%和 10%存活时的 RBE 分别为 2.6 和 1.9。在 50%存活时，用 8keV X 射线处理的细胞的 OER 为 1.6，而（60）Co 伽马射线为 3.0。用 8keV X 射线和（60）Co 伽马射线处理后每 Gy 的 H2AX 焦点数量相似；然而，在 8keV 时产生的焦点尺寸明显更大，可能表明更复杂的 DNA 损伤。8keV X 射线产生的 H2AX 焦点的平均面积为 0.785μm²（95%CI：0.756-0.814），而（60）Co 伽马射线为 0.491μm²（95%CI：0.462-0.520）（P<0.0001）。特征性的 8keV X 射线产生的生物学效应是兆伏光子的两到三倍，具有与更高 LET 辐射相似的放射生物学特征。
