Patients are exposed to X rays when undergoing medical examinations in diagnostic radiology. Exposure data acquired and assessed in Germany for the year 1997 resulted in a mean annual effective dose of 2 +/- 0.5 mSv per head of the population, thereby reaching or exceeding the average level of environmental radiation in many cases. The underlying frequency of medical X-ray examinations was approximate to 136 million, i.e.approximate to 1.7 examinations annually per head of the population. For comparison, corresponding data of other countries were extracted from the UNSCEAR 2000 report or originate from the literature. Data analysis shows significant differences in national radiological practices and a very uneven distribution of patient doses amongst the world population. The mean annual effective dose per head of the population varies by up to a factor of 60 between health care level I and IV countries, and still by a factor of approximate to 6 within health care level I countries. While projection radiography has succeeded in reducing dose consumption, computed tomography and radiological interventions have given rise to a significant growth of patient exposure, and interventional radiology can even exceed thresholds for deterministic radiation effects. Patient exposure is further shown to result from misadministration and retakes of X-ray examinations, usually not registered, as well as from technical failures of X-ray facilities, which can cause significantly enhanced exposure times. Corresponding data are presented and comments are made on the international situation of non-harmonised data collection on patient exposure as well as of parameters affecting the assessment of exposure and risk.
