Reference doses and quality in medical imaging.

Abstract

Numerous patient dose surveys have been perresult in deterministic effects being observed in formed in diagnostic radiology over the years. In patients. The drive for lower patient doses should the main, the results of these surveys indicate that not be undertaken without careful consideration there is a wide range in radiation exposure for of the clinical and hence the imaging requirements. nominally the same examination. Whilst variations This is particularly relevant in interventional radiin patient size and composition can explain some ology where the imaging tasks are quite difficult of the observed variation, there are other causes. and patient doses are high. Differences in radiation dose for nominally the In these circumstances reference doses should be same examination may vary by up to 100. It is used as a tool to indicate where optimization therefore obvious that there is some scope for dose studies may be useful. Any investigation into high reduction. doses must also consider two basic principles of In view of this wide variation, the International radiation protection, that is optimization and justiCommission on Radiological Protection (ICRP) fication. In interventional radiology the concept of promoted the use of diagnostic reference levels in justification is a complex issue, as the risks and Publication 73 [2]. Reference doses are intended benefits to the patient of alternative treatment to act as an indicator for dose levels above which options, as well as the radiation risks both to an investigation should be carried out. Doses to a patients and staff, need to be considered. The number of patients must consistently exceed the concept of reference doses is also applicable to all reference value for an investigation to occur. The other types of X-ray examinations, not just interlevels for particular examinations may be set ventional radiology, although the risk/benefit nationally, but some hospitals are already using relationship is different. lower levels. Various organizations agreed to their The workshop only partially managed to achieve establishment in the publication of the Basic Safety its stated objectives in that it did provide a forum Standards by the International Atomic Energy for the exchange and discussion of views on referAgency [3]. The concept of reference levels also ence doses, but there were few presentations on appears in a number of medical imaging quality image quality and so very limited debate on this criteria documents published by the European important aspect of the audit process. Without Commission [4–6] where, for the first time, it is careful consideration of the necessary image quality considered in parallel with the diagnostic inforto make the required diagnosis, an over zealous mation contained in the image. drive to lower doses could be at the expense of The workshop comprised a series of invited clinical outcome. In the United Kingdom, reference lectures and proffered posters. Many of the posters doses are based on third quartile values of the presented the results of patient dose surveys. distributions of the mean dose observed in many In a few, reference doses were deduced from the hospitals. Reducing doses in those centres already data presented. There appeared to be very little below the third quartile does not result in optim-