The role of effective dose in medicine now and into the future.

Effective dose was created as a radiological protection dose quantity linked to risk to enable planning of radiological protection for the control of exposure. Its application and use has evolved from occupational and public exposure during work with radiation sources to medicine and applications in patient dosimetry. Effective dose is the sum of doses to organs and tissues within the body weighted according to their sensitivity to radiation for induction of stochastic effects determined from epidemiological studies of exposed populations. It is based on radiation risks averaged over the population and formulated using reference phantoms. Effective dose has been adopted by the medical community for application to patients and has been instrumental in raisingawareness of doses from medical imaging. However, although effective dose can beused for comparison of doses from different medical procedures, it is not designed forapplication to individual patients. The reasons being that organ doses vary with the stature of the patient and the radiation risks depend on the age and sex of the patient. Moves to more personalised medicine have created a desire for a more individualised approach to patient dosimetry, although support for this progression is not universal. This paper traces the evolution of effective dose and its applications. It reflects on how well effective dose provides a measure of risk for individual patients and examines ways in which a more personalised approach might be developed with reference to computed tomography (CT). It considers differences in dose relating to the sizes of patients and looks at variations in risks of cancer incidence within a population with an age distribution typical of patients and examines how this relates to the risk profile. Possible options for improving the individualisation of dosimetry are discussed. .