Transition radiation as an x-ray source for radiobiology

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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.