Transition radiation as an x-ray source for radiobiology

我们希望考虑是否有可能开发一种可调的X射线源，用于生物细胞的显微探测，以便了解辐射诱发癌症的机制和利用辐射治疗肿瘤。辐射质量（它是能量的函数）是决定电离辐射生物有效性的关键属性。此外，调整能量的能力将允许控制探针的穿透。这对于使用培养的组织样本的研究非常有用。微探针技术在放射生物学中的优势在于它允许单个细胞，或者实际上是细胞群中细胞的单个部分被选择性地照射。这些方法正被用于研究细胞信号在辐射损伤中的作用。现在已知的是，这种损伤可以发生在未照射的细胞中，而照射的细胞是邻近的。这被称为旁观者效应，仍然知之甚少，但它对理解辐射风险以及什么构成安全剂量具有深远的影响，并且可能是改善放射治疗的可利用途径。到目前为止，低能量聚焦X射线的工作只能研究导致细胞死亡的影响，而不是更相关的（在辐射诱导的致癌作用研究中）细胞突变和转化，其诱导率低几个数量级。研究突变和转化需要高的细胞通量，这只有在源具有足够高的剂量率时才有可能。因此，除了调谐之外，还需要更高的通量率，并且这些需要对源和聚焦X射线光学器件中的一个或两个进行改进。

We wish to consider the possibility of developing a tuneable source of x-rays which could be used in the microprobing of biological cells, in order to lead to an understanding of the mechanisms of radiation-induced cancers and the treatment of tumours using radiation. Radiation quality (which is a function of energy) is a key property in determining the biological effectiveness of ionising radiation. Also, the ability to tune the energy will allow the penetration of the probe to be controlled. This is very useful for studies that use cultured tissue samples. The strength of the microprobe technique in radiobiology is that it allows individual cells or, indeed, individual parts of a cell within a cell population to be irradiated selectively. Such methods are being used to investigate the role of cell signalling in radiation damage. It is now known the damage can arise in unirradiated cells in proximity to irradiated cells. This is known as the bystander effect and remains poorly understood, but it has far reaching consequences for the understanding of radiation risk, and what constitutes a safe dose, and may be an exploitable pathway to improved radiotherapy treatment. So far, work with low energy focused x-rays has only been capable of investigating effects leading to cell death, rather than the much more relevant (in studies of radiation-induced carcinogenesis) cell mutations and transformations which have induction rates several orders of magnitude lower. To study mutation and transformation requires high cell throughputs which is only possible if the source has a sufficiently high dose rate. Thus, in addition to tuneability, higher flux rates are required and these need improvements to either or both the source and the focusing x-ray optic.