PRELIMINARY REFERENCE LEVELS FOR DIAGNOSTIC RADIOLOGY IN ESTONIA K. Kepler1, A. Servomaa2 and I. Filippova1 1 2
University of Tartu, Tartu, Estonia University of Oulu, Oulu, Finland
[email protected]
Abstract: The present survey of adult patient doses in x-ray diagnostics was carried out in 24 hospitals, covering thus 56% of hospitals and about 20% of conventional X-ray units in Estonia. Entrance surface dose (ESD) of the patient was assessed by indirect method, using data of radiation yield of x-ray tubes and examination technique. Data were collected for 1050 radiographs of adult patients. Average entrance surface doses varied by a factor of up to 5,5-12 between hospitals. The average doses in chest, lumbar spine and pelvis examinations do not exceed the European diagnostic reference levels (DRL), but are higher than the dose reference levels in Nordic countries. In this study the preliminary DRLs, based on the 3rd quartile of the dose distribution, have been suggested for chest PA examinations – 0,3 mGy, for chest LAT – 1 mGy, for lumbar spine AP – 7 mGy, for lumbar spine LAT – 12 mGy, for pelvis AP – 6 mGy. The recommended DRLs are preliminary, until the data collected through more comprehensive dosimetric surveys will be available. Likewise, it presumes implementing all requirements of the European Medical Exposure Directive (97/43/Euratom) concerning patient dosimetry into the national legislation in Estonia. Introduction About one million medical X-ray examinations are carried out each year in Estonia, corresponding on average to 0.7 examinations per head of population [1]. In 1997 the essentially voluntary system of patient dose management, developed by the International Commission on Radiological Protection, became mandatory in European Union [2]. By 1999 European Diagnostic Reference Levels (DRLs) were available in three sets of European Guidelines on quality criteria for radiographic examinations in adults or children, and for computed tomography examinations [3]. For now patient dose surveys are carried out in most of the Member States, and quite often it is done in the framework of international collaboration (e.g. Nordic survey [4]). In Estonia doses in pediatric radiology were studied from 1999 to 2002 [5]. Unfortunately there is no legal regulation for establishment of patient dose assessment system in Estonian radiology departments yet. A new regulation for use of radiation in medical radiology, following all requirements of Medical Exposure Directive (MED) [2], is in preparation in the Ministry of Social Affairs. The present study is the first attempt to evaluate patient doses in the majority of the Estonian health care institutions equipped with x-ray departments. The aim of this study was to measure average patient doses and to estimate preliminary reference doses for most typical examinations in radiology departments in Estonia. Materials and Methods The present survey of adult patient doses in X-ray diagnostics was carried out during the years of 2002- 2003. Dose measurements were carried out in 24 hospitals. The data were collected for 1050 radiographs of adult patients. The sample of patients was chosen so that the weight of the patients is between 60-80 kg and the average of the weight 70 ± 3 kg. Five typical x-ray examinations were chosen for the study: chest PA, chest LAT, lumbar spine AP, lumbar spine LAT, pelvis AP. The exposure factors (focus size, filtration, film-screen, grid, examination projection, tube potential, MAS, FFD, field size on film) were recorded along the details of patient age, gender, height, weight and focus-to-skin distance (FSD). The surface dose of the patient was assessed by an indirect method, using the radiation yield of the x-ray tube and examination techniques. The radiation output of the X-ray tube has been measured beforehand at the relevant tube voltage, focal spot and filtration. Using the measurements of the absorbed dose to the air, ESD was calculated by applying the inverse square law to obtain the dose at the FSD and by multiplying by the mean backscatter factor (1.35). Results The doses in chest PA examinations (Figure 1) vary by a factor of 12 between hospitals. The minimum value of the ESD in chest PA examinations is 0,05 mGy, the maximum value is 0,6 mGy.
The average doses in lumbar spine AP examinations vary by a factor of about 4 between hospitals. The minimum value of the ESD is 1,8 mGy, the maximum value of ESD is 10 mGy. Results in all different examinations are shown in Table 1 and the third quartile of the dose distribution and recommended DRLs are given in Table 2. Table 1: Number of radiographs, ESD minimum and maximum values, average ESD and European ESD reference values. Examination
Number of radiographs
Chest PA Chest LAT Lumbar spine AP Lumbar spine LAT Pelvis AP
272 241 200 229 108
Minimum ESD (mGy) 0,05 0,2 1,8 3,7 1,8
Maximum ESD (mGy) 0,6 2,3 10,0 21,8 10,0
Average ESD (mGy) 0,3 0,9 6,4 10,7 3,9
European DRL (mGy) 0,3 1,5 10 30 10
Table 2: Average ESD, estimated third quartile ESD and recommended dose reference levels (DRL) in Estonia. Examination Chest PA Chest LAT Lumbar spine AP Lumbar spine LAT Pelvis AP
Average ESD (mGy) 0,31 0,9 6,4 10,7 3,9
Third quartile ESD (mGy) 0,36 1,1 6,9 11,7 5,7
Recommended DRL (mGy) 0,3 1,0 7,0 12,0 6,0
Discussion The average doses vary by a factor of up to 4-12 between hospitals, which can be explained by differences in the radiology equipment and techniques. Average ESD for chest, lumbar spine and pelvis examinations in the most of the hospitals in Estonia does not exceed the European diagnostic reference levels [3]. Average ESD in chest PA examination is of the same value as the European reference level. But it can be also estimated, that the estimated doses are higher than in Nordic countries [4]. Conclusions Quantitative methods for assessment of patient doses should be implemented in all radiology departments. The recommended DRLs are preliminary, until the data collected through more comprehensive dosimetric surveys are available. It presumes implementing of all requirements of the MED [2] into the national legislation in Estonia. Cooperation between the professional societies and the national authorities responsible for creation of the national legislation and sustainable system of quality assurance including patient dose optimisation in Estonia is necessary. References [1] THOMSON H., RUUGE M., RÄTSEP M., TEEMUSK L. (Editors) (2003): ‘Estonian health statistics 2000-2002’, (Ministry of Social Affairs, Tallinn) [2] COUNCIL OF EUROPEAN UNION (1997): ‘Council Directive 97/43/EURATOM of 30 June 1997 on health protection of individuals against the dangers of ionizing radiation in relation to medical exposure, and repealing Directive 84/466/EURATOM’, Official Journal of the European Communities, 40 (L 180), pp. 22-27 [3] EUROPEAN COMMISSION (1999): ‘Radiation Protection 109: Guidance on diagnostic reference levels (DRLs) for medical exposures’, (Office for Official Publications of the European Communities, Luxembourg) [4] GRON B., OLERUD H., EINARSSON G., LEITZ W., SERVOMAA A., SCHOULTZ B. and HJARDEMAAL O. (2000): ‘A Nordic survey of patient doses in diagnostic radiology’, Eur. Radiol., 10, pp.1988-1992 [5] KEPLER K., LINTROP M., SERVOMAA A., FILIPPOVA I., PARVIAINEN T. and EEK V.(2003): ‘Radiation dose measurement of paediatric patients in Estonia’, in: ‘STUK-A195: Radiation Protection in the 2000s – Theory and Practice’, (Finnish Radiation and Nuclear Safety Authority, Helsinki), pp. 287-292
