At what dose levels should we be concerned about overexposure of patients?

European legislation, in accordance with the recommendations of the International Commission on Radiological Protection, requires that the radiation dose to patients, once 'justified', is 'optimised', i.e for diagnostic exposures the dose is kept low while still providing a clinically useful image and for therapeutic exposures the dose to the target volume is maximised while minimising the dose to healthy tissue. Unfortunately, due to equipment faults or human error, patients sometimes receive a higher dose than required and are therefore at a higher than necessary risk of stochastic or deterministic detriment. Additionally, in radiotherapy, doses that are lower than planned may have serious consequences unless discovered and corrected. This paper presents examples of reported incidents and the risks of detriment are discussed. The requirements for reporting of such events to regulatory authorities are described. These are generally based on the linear, no threshold model of the relationship between radiation dose and detriment. In some cases national regulatory authorities require individual reporting of relatively small overexposures and these require significant effort to investigate. The authors suggest that the resource required is disproportionate to the risk and detracts from work to reduce the number of incidents involving greater overexposures. It is proposed that authorities should only require individual investigations and reports of overexposure incidents where there is a significant risk of radiation detriment to the patient and a threshold for this risk is suggested. Incidents involving an overexposure factor less than this threshold should be recorded and statistical data supplied to the authorities at stipulated intervals. The statistical data can be analysed and used to assess areas where effort needs to be concentrated with the need for detailed investigation of individual incidents. (author)