Radiobiology

CT is a relatively high radiation dose examination, and there are some important issues to consider in radiobiology; CT now accounts of almost 25% of all radiation exposure in the United States of America. Cells, tissues and organs respond to radiation in ways that are random (stochastic) that primarily act at the cellular level and more predictable (deterministic), with threshold doses that act at the tissue level. Tissue weighting factors and effective dose are considered, cognisant with the radiation doses given by CT. Typical effective doses for many typical CT examinations are available, but this does not imply that all examinations of this type result in a particular effective dose – they are estimates that do not take into account such factors as the size of the patient, type of procedure and the equipment used. In particular, the issue of ‘low dose CT’ in screening examinations is considered – as doses here may be considerably less, by up to 50%. CT examinations that have the potential to have a high radiation burden are considered, for example CT angiography and CT colonography. There is a focus on particular patient groups that have a greater potential for risk, with emphasis on the paediatric patient group. Risks from radiation will be considered in context with the many benefits drawn from a well-managed CT examination. From this chapter, the reader gains a solid understanding of the radiobiological effects of radiation at the level of dose given by CT.