Craven P A, Rycroft M J
Institute of Cancer Research, University of London, London, UK.
Adv Space Res. 2005;35(2):300-4. doi: 10.1016/j.asr.2004.09.016.
Amongst the great variety of heavy particles present in the galactic and solar cosmic ray spectra, hydrogen and helium nuclei are significantly more abundant than all other heavier ions and, as such, represent a major radiation hazard to humans in space. Experimental data have suggested that differences in relative biological effectiveness (RBE) exist between the two species at the same value of linear energy transfer (LET). This has consequences for heavily ionising radiation protection procedures, which currently still assume a simple dependence of radiation quality on LET. By analysing the secondary electron (delta-ray) emission spectra of protons and alpha particles, in terms of the spatial characteristics of energy deposition in cellular targets and the likelihood of complex lesion formation, a numerical quantity representing biological effectiveness is generated. When expressed relative to a reference radiation, this quantity is found to differ for protons and a particles of the same LET, demonstrating not only the ion-specific nature of RBE but also the inadequacy of specifying radiation quality as a function of LET only. Such a method for numerically assessing radiation quality may have implications for procedures for heavy ion protection in space at low doses and for understanding the initial mechanisms of radiation action.
在银河系和太阳宇宙射线谱中存在的种类繁多的重粒子中，氢核和氦核的丰度明显高于所有其他较重离子，因此，它们是对太空中人类的主要辐射危害。实验数据表明，在相同的线能量转移（LET）值下，这两种粒子的相对生物效应（RBE）存在差异。这对重离子辐射防护程序产生了影响，目前这些程序仍然假定辐射质量仅简单地依赖于LET。通过分析质子和α粒子的二次电子（δ射线）发射光谱，从细胞靶点中能量沉积的空间特征和复杂损伤形成的可能性来看，可以生成一个代表生物效应的数值量。当相对于参考辐射表示时，发现相同LET的质子和α粒子的这个量是不同的，这不仅证明了RBE的离子特异性，也表明仅将辐射质量指定为LET的函数是不够的。这种数值评估辐射质量的方法可能对低剂量空间重离子防护程序以及理解辐射作用的初始机制有影响。
