Since the introduction of the Ionising Radiation (Medical Exposure) Regulations in 2000 (IR(ME)R 2000) [1
], employers responsible for the use of dental and medical X-ray equipment have been required to establish local diagnostic reference levels (DRLs) for each common radiographic procedure undertaken. Reviews of their radiography practices are required if DRLs are consistently exceeded. In effect, a diagnostic reference level can be considered the level of dose expected not to be exceeded for a standard procedure when good and normal practice regarding diagnostic and technical performance is applied. Local DRLs should be established by the employer in consultation with the appointed medical physics expert (MPE).
To assist employers to set appropriate local DRLs, the Department of Health adopted national DRLs for many common X-ray examinations [2
]. National DRLs are normally set at the third quartile value of the patient dose distribution observed for a particular type of X-ray examination during a widescale survey (i.e.
the patient dose value that only 25% of assessed X-ray sets exceed).
The national DRLs adopted by the Department of Health were primarily based on the Health Protection Agency’s (HPA) 2000 review of the National Patient Dose Database (NPDD) [3
]. However, at the time of the review, dental X-ray examinations were not included in the NPDD. Subsequently, the national DRL for dental intra-oral examinations was based on separate patient dose data published by the HPA in 1999 [4
The NPDD was designed to collate measurements of patient radiation doses from common diagnostic X-ray examinations carried out throughout the UK and to provide a major source of information for the review and adoption of new national DRLs. In July 2007, the HPA published the 2005 review of the NPDD [5
]; this time, the review included dose data from dental X-ray examinations and proposed new National Reference Doses (NRDs) for intra-oral and panoramic examinations, which updated those first proposed in 1999 [4
]. Although these NRDs for intra-oral and panoramic examinations have not been formally adopted by the Department of Health as national DRLs, the data collected are representative of current practice.
When setting a local DRL, national DRLs and NRDs should be considered and it would be expected that the local DRL should not normally exceed the national level. However, just ensuring that patient doses are below the national DRL or NRD does not mean that local practices are being optimised. Dental surgeries using modern equipment and techniques should be able to set a local DRL significantly lower than the national level, based on their local circumstances.
A national review of doses arising from dental cephalometric examinations has never been undertaken in the UK and cephalometric doses have not, to date, been included in the NPDD. For many years, however, the Dental X-ray Protection Service (DXPS) of the HPA has carried out the commissioning and routine quality assurance testing of cephalometric equipment installed throughout the UK. As part of the testing procedures, measurements are made of representative patient doses. This report proposes a patient dose measurement method together with rounded third quartile dose values for adult and child lateral cephalometric radiography based on the patient dose measurements made by DXPS.
Owing to the specialist applications of cephalometric radiography, there are only a relatively small number of units in use in the UK compared with intra-oral or panoramic equipment; consequently, the sample size considered in this report is fairly small. However, the dose measurements are considered reasonably representative of UK practice so that the third quartile values can be considered as provisional NRDs and provide a useful guide to employers when establishing their local DRLs. Furthermore, it is anticipated that the patient dose data presented in this report and any data subsequently collected on cephalometric radiography doses will be included in the NPDD so that future reviews of the database can propose NRDs for cephalometric radiography.