Patient exposure levels and collective effective dose to the population from radiological examinations - changes from 2008 to 2018 in Finland

Medical exposures from x-rays and nuclear medicine (NM) have been the largest man-made source of population exposure to ionizing radiation in developed countries for many years. A collective effective dose can be assessed by summarizing effective doses from all radiological examinations together. The collective effective dose is the product of the mean effective dose in a group and the number of individuals in that group. The most common method to assess effective doses per radiological examinations is to use application specific measurable quantities that are multiplied by predefined effective dose conversion factors. Frequencies of radiological examinations can be surveyed by questionnaires. In Finland the total collective effective dose from x-ray and NM procedures has increased 59% in 2008–2018, mainly due to the increase of collective effective doses from computed tomography (CT) and interventional radiology. The collective effective dose from NM examinations has slightly increased and its relative proportion is only 5% of the total collective dose from radiological examinations. About 70% of the collective effective dose from x-ray examinations was caused by CT in 2018, while the proportion of CT procedures was only 17%. CT procedures are the major and increasing source of collective effective dose from x-ray procedures. While the use of new tissue weighting factors (ICRP 103) increases the population dose from plain radiography, it has minimal effect on the population dose from CT examinations. There was a large amount of variation in the exposure levels and exposure parameters used for radiotherapy simulations. Patient exposure levels were generally much higher than those used for diagnostics. Exposure parameters should be reviewed and optimized together with the exposure level also for radiotherapy CT simulations. Effective doses per radiological examinations can be used to compare medical exposures from different methodologies or between different units or hospitals. Per caput doses can be compared between countries. In comparison with 36 European countries is was shown that frequencies of both x-ray and NM examinations in Finland were less than in average in Europe. This indicates that the level of justification in Finland is at least at the average European level. The comparison of per caput effective doses showed that the dose in Finland was on the lowest quarter among European countries. Despite of the increased collective effective dose from x-ray and NM examinations the overall per caput effective dose in Finland in 2018 was still well below the average of European countries in 2008 and only a third of the per caput effective dose in USA in 2016. This indicates that both justification and optimization of examinations in Finland is at a good European level