An EU-funded project called DOSE DATAMED (2004 - 2007) was set up to develop methods for future surveys of population exposure from medical x-rays, including issuing guidance on suitable patient dose quantities and dosimetry methods. The work has been published in the European Commission website as Radiation Protection Report No 154 with two separate annexes  .
The main report is available under the following link:
In order to assess population exposures from medical radiology in terms of the collective or per caput effective dose, it is necessary to estimate representative mean effective doses for each type of x-ray examination that makes a significant contribution to the annual collective effective dose (S) in a country. As the effective dose cannot be measured directly other dose quantities must be used.
Practical dose quantities are entrance surface dose or the dose-area product for simple radiography, the total dose-area product for fluoroscopy examinations, and the computed tomography dose index and the dose-length product for CT examinations. Factors for converting these dose quantities into effective doses are provided in RP154. Guidance on assessing the frequencies of x-ray examinations includes the definition of 225 specific x-ray examinations and 70 broader categories of examinations. A set of 20 examinations were identified as the ones contributing most significantly to S.
Typical dose figures for those examination types are provided, as well as guidance on how to perform frequency and dose surveys and a pragmatic method to assess the uncertainties involved. It is expected that the DOSE DATAMED concept will simplify the assessment of population exposures in medical radiology, and will furthermore improve the quality and comparability of results from various countries in the future.
The first aim was however to understand the uncertainties and differences in the current methodologies used for such surveys. National surveys in ten European countries around the millennium were reviewed in order to explain the differences seen in examination frequencies and patient doses, and their mutual influence on the annual collective effective dose (S) in each country. The national regulatory frameworks, the health care systems, the methods for assessing frequencies and doses, as well as the national strategies for assessing population dose from medical x-rays, were reviewed. A pragmatic method for estimation of the uncertainty in the assessment of S was developed and tested for three countries. A set of 20 examinations was identified as those contributing most significantly to S, the so called “TOP 20” list. The “TOP 20” results around the year 2000 from ten European countries has been presented, compared and discussed in various international forum such as IRPA 12 in Buenos Aires (link to poster1 and link to poster 2) and ECR 2009 in Vienna (link to ppt presentation). In conclusion the observed differences in the population dose from medical x-rays in Europe were thought to be real, i.e. much larger than the recognized uncertainties originating from survey design. Furthermore, the differences were found to be primarily due to the different healthcare systems operating in each country, which resulted in considerable variations in the amount of equipment and manpower devoted to medical radiology and in the financial incentives for carrying it out. The first report DD1 from DOSE DATAMED is published as Annex 1 to the RP Report No 154  and may be downloaded here:
A similar review was also done for nuclear medicine surveys, report DD1 (a) is published as Annex 2 to the RP Report No 154  , and may be downloaded here:
HERCA was created in 2007 at the initiative of the French Nuclear Safety Authoritiy (ASN). Since 2008 it is chaired by Mr. Ole Harbitz, Director General of the Norwegian Radiation Protection Authorities. Its activities are carried out by five Working Groups. HERCA WG “SURVEILLANCE OF COLLECTIVE DOSES FROM MEDICAL EXPOSURES” was established in 2009, and forms a network of expert organizations involved in population dose estimations. The purpose is to encourage national population dose estimates consistent with European guidance given in the report Radiation Protection No. 154  , and to update and share information about national initiatives and experiences on nationwide surveys of x-ray examination frequencies and patient doses in Europe. In the framework of HERCA, it has been collected information about more recent frequencies and doses for the 20 examinations that was identified as those contributing most significantly to the collective effective dose. New information was provided from 14 European countries, and the results were presented at the IRPA conference in Helsinki, Finland 14. – 18. June 2010 (link to www.irpa2010europe.com, ppt presentation and paper) During the DDM2 project period, according to the last HERCA board minutes (link), WG6 will remain as a “sleeping WG” as its mandate will be carried out by DDM2 including more countries than those in the current contact list of WG6.
 European guidance on estimating population doses from medical x-ray procedures and annexes. Radiation protection no. 154. Brussels: European Commission, Directorate General for Energy and Transport, 2008. http://ec.europa.eu/energy/nuclear/radioprotection/publication/doc/154_en.zip