Endo Satoru, Hoshi Masaharu, Takada Jun, Takatsuji Toshihiro, Ejima Yosuke, Saigusa Shin, Tachibana Akira, Sasaki Masao S
Research Institute for Radiation Biology and Medicine, Hiroshima University, Japan.
J Radiat Res. 2006 Jun;47(2):103-12. doi: 10.1269/jrr.47.103.
A characteristic hot-filament type X-ray generator was constructed for irradiation of cultured cells. The source provides copper K, iron K, chromium K, molybdenum L, aluminium K and carbon K shell characteristic X-rays. When cultured mouse m5S cells were irradiated and frequencies of dicentrics were fitted to a linear-quadratic model, Y = alphaD + betaD2, the chromosomal effectiveness was not a simple function of photon energy. The alpha-terms increased with the decrease of the photon energy and then decreased with further decrease of the energy with an inflection point at around 10 keV. The beta-terms stayed constant for the photon energy down to 10 keV and then increased with further decrease of energy. Below 10 keV, the relative biological effectiveness (RBE) at low doses was proportional to the photon energy, which contrasted to that for high energy X- or gamma-rays where the RBE was inversely related with the photon energy. The reversion of the energy dependency occurred at around 1-2 Gy, where the RBE of soft X-rays was insensitive to X-ray energy. The reversion of energy-RBE relation at a moderate dose may shed light on the controversy on energy dependency of RBE of ultrasoft X-rays in cell survival experiments.
构建了一种用于照射培养细胞的具有特色的热丝型X射线发生器。该源可提供铜K、铁K、铬K、钼L、铝K和碳K壳层特征X射线。当对培养的小鼠m5S细胞进行照射并将双着丝粒频率拟合到线性二次模型Y = αD + βD²时，染色体效应并非光子能量的简单函数。α项随着光子能量的降低而增加，然后随着能量的进一步降低而降低，在10 keV左右有一个拐点。β项在光子能量降至10 keV之前保持恒定，然后随着能量的进一步降低而增加。在10 keV以下，低剂量时的相对生物效应（RBE）与光子能量成正比，这与高能X射线或γ射线的情况形成对比，在高能情况下RBE与光子能量呈反比。能量依赖性的反转发生在约1 - 2 Gy处，此时软X射线的RBE对X射线能量不敏感。中等剂量下能量 - RBE关系的反转可能有助于解释细胞存活实验中关于极软X射线RBE能量依赖性的争议。
