National reference doses for common radiographic, fluoroscopic and dental X-ray examinations in the UK

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1 The British Journal of Radiology, 82 (2009), 1 12 COMMENTARY National reference doses for common radiographic, fluoroscopic and dental X-ray examinations in the UK D HART, PhD, M C HILLIER and B F WALL, BSc Radiation Protection Division, Health Protection Agency, Chilton, Didcot, Oxon OX11 0RQ, UK ABSTRACT. The National Patient Dose Database (NPDD) is maintained by the Radiation Protection Division of the Health Protection Agency. The latest review of the database analysed the data collected from 316 hospitals over a 5-year period to the end of The information supplied amounted to a total of entrance surface dose measurements and dose area product measurements for single radiographs, and dose area product measurements along with fluoroscopy times for diagnostic examinations or interventional procedures. In addition, patient dose data for dental X-ray examinations were included for the first time in the series of 5- yearly reviews. This article presents a summary of a key output from the NPDD national reference doses. These are based on the third quartile values of the dose distributions for 30 types of diagnostic X-ray examination and 8 types of interventional procedure on adults, and for 4 types of X-ray examination on children. The reference doses are approximately 16% lower than the corresponding values in the previous (2000) review, and are typically less than half the values of the original UK national reference doses that were derived from a survey in the mid-1980s. This commentary suggests that two of the national reference doses from the 2000 review be retained as diagnostic reference levels because the older sample size was larger than for the 2005 review. No clear evidence could be found for the use of digital imaging equipment having a significant effect on dose. Received 2 May 2008 Revised 7 July 2008 Accepted 15 July 2008 DOI: /bjr/ The British Institute of Radiology The National Patient Dose Database (NPDD) was established in 1992 by the National Radiological Protection Board (NRPB) after the publication of a National Protocol for Patient Dose Measurements in Diagnostic Radiology [1]. The purpose of the NPDD was to collate the measurements of radiation doses to patients from common radiographic and fluoroscopic X-ray examinations carried out in hospitals throughout the UK, and to monitor any trends. The NRPB was merged into the Health Protection Agency in April 2005, as its Radiation Protection Division (RPD). The RPD is responsible for maintaining the NPDD, and will continue to publish reviews recommending national reference doses approximately every 5 years. Three reviews of the data have been published for each of the 5-year periods preceding 1995, 2000 and 2005 [2 4]. The latest review [4] was published in August A total of more than 700 hospitals and clinics have contributed data to one or more of these reviews. The Ionising Radiation (Medical Exposure) Regulations 2000 [5] (IR(ME)R) introduced a legal framework for the establishment of diagnostic reference levels (DRLs) in the UK. Guidance on the establishment Address correspondence to: D Hart, Radiation Protection Division, Health Protection Agency, Chilton, Didcot, Oxon OX11 0RQ, UK. E- mail: david.hart@hpa.org.uk and use of DRLs for medical and dental X-ray examinations was prepared by a joint working party of relevant professional bodies and published by the Institute of Physics and Engineering in Medicine (IPEM) in 2004 [6]. This guidance recommended that the national reference doses published in the 5-yearly reviews of the NPDD be a major source for national DRLs. Indeed, in April 2007, the English Department of Health formally adopted [7] the national reference doses recommended in the 2000 review of the NPDD as national DRLs for radiographic and fluoroscopic X-ray examinations in compliance with IR(ME)R. This article discusses the subsequent 2005 review of the NPDD, presents the latest national reference doses, and discusses their potential impact on future revisions of the national DRLs by the Department of Health. Radiation doses from dental X-ray examinations have been included for the first time in the latest 5-yearly review. Dental practices usually have limited access to radiation protection expertise, and national reference doses can be an important aid to the optimization of patient doses in these circumstances. It is intended that national reference doses for dental X-ray examinations will be included in future reviews of the NPDD. Radiation doses to patients from CT examinations are not included in the NPDD. Such information is stored in a separate database, also maintained by the RPD, called PREDICT (Patient Radiation Exposure and Dose In CT). The British Journal of Radiology, January

2 D Hart, M C Hillier and B F Wall It is intended that the data in PREDICT will be reviewed at regular intervals in a similar manner to NPDD. The latest review of the PREDICT database includes national reference doses for eight common types of CT examination and was performed for the year 2003 [8, 9]. The Department of Health has also formally adopted [7] these reference doses as national DRLs in compliance with IR(ME)R. Methods Dose measurements were collected for: 1. Non-dental radiographs and examinations. Measurements included entrance surface dose (ESD), dose area product (DAP) and fluoroscopy times, taken according to the National Protocol [1]. 2. Dental radiographs and examinations. These measurements included the absorbed dose to air at the tip of the collimator for intra-oral radiographs, and the dose width product (DWP, i.e. the dose multiplied by the beam width as measured at the post-patient collimator) and DAP for panoramic radiographs, taken according to IPEM guidance [6]. In addition to dose measurements, data were collected on the patient (e.g. age, sex and weight, but not identity), the radiological equipment used and the examination technique (see Appendix B of [4]). 97% of the dose measurements for the 5-year period to 2005 related to non-dental examinations and were supplied by hospital physicists, radiographers and radiologists from throughout the UK. 1% of the data came from the RPD s Patient Dosimetry Service, which used thermoluminescent dosemeters to measure ESDs for simple radiographic examinations performed in hospitals. Doses from dental practices constituted the rest of the data (2%). More than two-thirds of the dental dose measurements came from the Dental X-ray Protection Service (DXPS) of the RPD [10]. The remainder was supplied by seven medical physicists who provide radiation protection advice to dentists. For most X-ray examinations, patient doses increase with patient size. To circumvent this variation, the data were analysed in terms of the mean patient dose for a specific examination within a specific room. The National Protocol for Patient Dose Measurements in Diagnostic Radiology recommends that the mean weight of a sample of patients in a specific room should lie in the range kg for the mean dose to be indicative of the typical dose to an average (70 kg) adult patient. Not all data providers followed this recommendation when submitting data to the NPDD, and many did not supply any information on patient weight. Consequently, dose data for adult patients were only included in this review if the mean patient weight was in the range kg, or if the patient weight was unspecified but there was a minimum of 10 patients per room. These are the same selection criteria as used in the 2000 review [3] and resulted in rejection of,20% of the data supplied. Approximately 4% of all the dose measurements in the latest database relate to children. For medical X-ray examinations, a method has been developed previously [11] for adjusting doses measured in children of any age to derive the dose that would have been given to the nearest standard-sized patient representing a 0-, 1-, 5-, 10- or 15-year-old child. This method was applied to the limited amount of data from paediatric patients in the NPDD, where the required information on the thickness of the body part being X-rayed, or the height and weight of the patient, was included. For dental X-ray examinations, a single dose measurement is made on each dental radiograph set using typical exposure conditions for an adult or a child, but without a patient present. There is therefore no need to select the data on the basis of patient size. Results For hospital X-ray examinations, ESD measurements, DAP measurements for single radiographs, and DAP measurements along with fluoroscopy times for complete diagnostic examinations or interventional procedures were stored in the database before data selection criteria were applied. The data came from 316 hospitals from all regions of the UK, from all sizes of hospital, and from both the NHS and the independent sector. This sample covers,23% of all hospitals and clinics with diagnostic X-ray facilities in the UK. The dental X-ray data came from approximately 3000 dental clinics in all regions of the UK (i.e. about 25% of all dental clinics in the UK [12]) and consisted of: 1. more than 6000 measurements of the absorbed dose to air at the tip of the collimator for intra-oral radiographs; 2. over 2200 measurements of DWP and nearly 2000 measurements of DAP for panoramic radiographs. Figure 1 compares the 2005 review histograms of room mean ESDs for several common radiographs with corresponding histograms from the 1995 and 2000 reviews. The third quartiles of the room mean ESD values are indicated by a vertical line on the histograms, and it can be seen that they have become progressively lower with each review for most radiographs. It can also be seen that the high-dose tails of the distributions have largely decreased over the years and the distributions have become slightly narrower, but not as much as might be expected if all hospitals exceeding the reference doses had taken corrective action. Figure 2 compares the histograms of the room mean DAP values for four barium studies over the three reviews: 1995, 2000 and The third quartile values have in general decreased slightly over the three reviews, but the high-dose tails do not show much indication of shortening. Figures 3 and 4 compare the third quartile values over 10-year intervals since the original survey in 1985 [13] for those radiographs and examinations with sufficient data. It can be seen that the third quartiles have steadily decreased. For hospital X-ray examinations, a comparison was made between the doses from digital systems (i.e. 2 The British Journal of Radiology, January 2009

3 Commentary: National reference doses for the UK Figure 1. Comparison of room mean entrance surface dose (ESD) distributions for all three reviews. AP, anteroposterior; LAT, lateral; LSJ, lumbosacral joint; PA, posteroanterior. The British Journal of Radiology, January

4 D Hart, M C Hillier and B F Wall Figure 1. Continued. 4 The British Journal of Radiology, January 2009

5 Commentary: National reference doses for the UK Figure 1. Continued. computed radiography (CR) and flat panel detectors) and doses from film-screen systems [4]. A Student s t-test on the ESD for 10 common types of radiograph showed that the mean ESD for CR was significantly different at the 98% confidence level to that for film for four types of radiograph only. For all four of these radiograph types, the mean CR dose was less than that for film by 40 50%. Regarding the DAP per radiograph, a Student s t-test showed that the mean CR dose was not significantly different to that for film for each of the 10 types of radiograph. For flat-panel detectors, which were mainly used in cardiac catheterization laboratories, a similar comparison with conventional systems (i.e. those not involving CR or flat-panel detectors) for eight procedures indicated no significant difference in the mean DAP values for any of the procedures. Overall, therefore, digital systems gave similar doses to film-screen systems. When considering this result, it should be borne in mind that the average film-screen speed is now,530, compared with 390 for the 2000 review. National reference doses In the 5-yearly reviews of the NPDD, national reference doses for common X-ray examinations are based on third quartile values of the mean patient doses observed in a nationally representative sample of X-ray rooms. Reference doses set at this level provide an indication of when the imaging equipment or examination techniques used in a particular X-ray room are producing unusually high doses and, if exceeded, should lead to further investigation and corrective action. They also provide a major source of data for consideration by the Department of Health when formally adopting national diagnostic reference levels in accordance with IR(ME)R, as discussed earlier. Adult patients On the assumption that a minimum of about 20 rooms is necessary (as adopted in the previous reviews), there are sufficient data on both ESD and DAP per radiograph in the 2005 review to recommend reference doses in terms of both these quantities for the 11 types of radiograph shown in Table 1. The reference doses are given to two significant figures. The number of rooms supplying data for each radiograph is also indicated in the table (and for each subsequent table of national reference doses for non-dental examinations). The latest set of national reference doses for 17 types of complete diagnostic examination, in terms of both the total DAP and the total fluoroscopy time for the examination, is shown in Table 2. As in the previous review, water-soluble enemas and swallows have been combined with barium enemas and swallows and given the same reference doses as in Table 2, as the respective DAP values and fluoroscopy times are similar for these examinations when performed with the two types of contrast media. As was found in the previous review, the The British Journal of Radiology, January

6 D Hart, M C Hillier and B F Wall Figure 2. Comparison of room mean dose area product (DAP) distributions for all three reviews. mean weight of coronary angiography patients was above the normal selection range (65 75 kg). A range of kg was therefore used for this examination in order to maximize the sample of patients. (The kg range was also used for percutaneous transluminal coronary angioplasties (PTCAs), as shown in Table 3.) Table 3 shows the latest set of national reference doses for eight interventional procedures, in terms of both total DAP and total fluoroscopy time. Biliary drainage and biliary intervention procedures have been combined in Table 3, as the respective DAP values and fluoroscopy times were very similar for both types of procedure. 6 The British Journal of Radiology, January 2009

7 Commentary: National reference doses for the UK Figure 3. Third quartiles for entrance surface dose (ESD) for radiographs. AP, anteroposterior; LAT, lateral; LSJ, lumbosacral joint; PA, posteroanterior. Biliary interventions and PTCAs have the highest reference dose (50 Gy cm 2 ) of all the procedures and examinations listed in Tables 2 and 3. The national reference doses in Tables 1 3 are, in general, slightly lower than or equal to the corresponding reference doses for the 2000 review. The exceptions (with the percentage by which they are higher shown in brackets) are the ESD reference dose for thoracic spine anteroposterior (AP) (14%), the DAP/examination for barium meals (8%), femoral angiography (9%), sialography (25%) and venography (40%), and the fluoroscopy times for femoral angiography (10%), nephrostography (4%) and sialography (6%). (For barium meals and femoral angiography, the sample sizes were smaller Figure 4. Third quartiles for dose area product (DAP) per examination. IVU, intravenous urography. The British Journal of Radiology, January

8 D Hart, M C Hillier and B F Wall Table 1. National reference doses for individual radiographs on adult patients 2005 review Radiograph ESD per radiograph (mgy) DAP per radiograph (Gy cm 2 ) Abdomen AP Chest LAT Chest PA Lumbar spine AP Lumbar spine LAT Lumbar spine LSJ Pelvis AP Skull AP/PA Skull LAT Thoracic spine AP Thoracic spine LAT ESD, entrance surface dose; DAP, dose area product; AP, anteroposterior; LAT, lateral; LSJ, lumbosacral joint; PA, posteroanterior. than for the 2000 review. An analysis later in this Commentary (see Table 6) indicates that the apparent increases for these two examinations may not be reliable.) Paediatric patients As in the 2000 review, there were only three medical X-ray examinations on children where sufficient data on patient size were available to estimate doses for each of the five standard sizes from at least 20 rooms. Table 4 shows the national paediatric reference doses based on the third quartiles of room mean DAP for these three examinations at each standard age corresponding to the standard size. The third quartile values of the doses for the 1-year-old and 5-year-old standard-sized patients differ only slightly between all three examinations (as was found in the 2000 review). It is therefore recommended that the same reference dose be used for both ages, and the value is shown in brackets in Table 4. Doses to 15-year-olds for micturating cystourethrogaphy, barium meals and barium swallows are a factor of times lower than those to adults. Therefore, there is a need (as in the previous review) to have separate reference doses for 15-year-olds and adults. The national reference doses in Table 4 are, in general, slightly lower than or equal to the reference doses for the 2000 review. The only exception to this is a barium swallow for a 10-year-old, which is now slightly higher. It may be noted that these national reference doses are higher by a factor of 4 10 than the local DRLs in use at the Great Ormond Street Hospital for Sick Children in 2004 [14]. Although paediatric dose data from that hospital were supplied for this review, it did not include the information on patient size that is necessary for deriving the standard age doses shown in Table 4 [11]. The low patient doses reported from Great Ormond Street Hospital demonstrate what is possible when paediatric radiography is fully optimized by dedicated paediatric staff. Dental radiography In 1999, Napier [15] presented reference doses for dental radiography based on a survey of over 6000 intra- Table 2. National reference doses for diagnostic examinations on adult patients 2005 review Examination DAP per exam (Gy cm 2 ) Fluoroscopy time per exam (min) Barium (or water-soluble) enema Barium follow through Barium meal Barium meal and swallow Barium (or water-soluble) swallow Coronary angiography a Femoral angiography Fistulography Hysterosalpingography IVU MCU Nephrostography Sialography Sinography Small bowel enema T-tube cholangiography Venography DAP, dose area product; IVU, intravenous urography; MCU, micturating cystourethrogaphy. a kg. 8 The British Journal of Radiology, January 2009

9 Commentary: National reference doses for the UK Table 3. National reference doses for interventional procedures on adult patients 2005 review Interventional procedure DAP per exam (Gy cm 2 ) Fluoroscopy time per exam (min) Biliary drainage/intervention Facet joint injection Hickman line Nephrostomy Oesophageal dilation Oesophageal stent Pacemaker PTCA (single stent) a DAP, dose area product; PTCA, percutaneous transluminal coronary angiography. a kg. oral X-ray sets and nearly 400 panoramic X-ray sets by the NRPB Dental X-ray Protection Service between 1995 and The recommended national reference doses were 4 mgy for adult intra-oral radiography and 65 mgy mm DWP for adult panoramic radiography. IPEM Report 91 based its remedial levels for patient doses in dental radiography on Napier s national reference doses [16]. National reference doses for dental radiography have not previously been included in the reviews of the NPDD, but were presented for the first time in the 2005 review. They are shown in Table 5, and are based on the third quartiles of the dose distributions seen in a sample of,3000 dental clinics throughout the UK. The number of dental X-ray sets on which measurements were made is indicated in Table 5. The new adult reference dose for intra-oral radiographs (2.3 mgy) is,40% lower than the 1999 value (4 mgy), probably owing to the use of faster film-screen and digital systems. This is the first time that a national reference dose for intra-oral radiographs on children has been recommended (1.5 mgy), and it is,35% lower than the corresponding adult value. Doses for panoramic radiographs on adults and children were found to be very similar, so it was not Table 4. National reference doses for diagnostic examinations on paediatric patients 2005 review Examination Standard age (year) DAP per examination (Gy cm 2 ) MCU (0.8) (0.8) Barium meal (1.2) (1.2) Barium swallow (1.3) (1.3) Valuesinbracketsareforthecombined1 5yearsagegroup. DAP, dose area product; MCU, micturating cystourethography. considered necessary to have separate national reference doses for these two types of patient. The national reference doses for panoramic radiographs shown in Table 5 are expressed in terms of both DWP and DAP, and apply to both adults and children. The new DWP reference dose for panoramic radiography is only,10% lower than the 1999 reference dose. There are advantages in expressing the reference dose for panoramic radiography in terms of DAP rather than DWP. It is more consistent with the approach adopted for medical X-ray examinations and is more closely related to patient dose, as the DAP measured at the post-patient collimator (in the absence of the patient) is, to a first approximation, the same as the DAP measured at the patient s entrance surface. DAP values can be derived from the DXPS data, as the height as well as the width of the X-ray beam is measured in the DXPS postal service. DAP is consequently likely to become the preferred patient dose quantity for panoramic dental radiography in the future [6]. Discussion Consideration will need to be given as to which reference doses should be formally adopted as national DRLs in accordance with IR(ME)R. When considering this issue, it is relevant to examine whether there is a significant difference between the third quartiles for the 2005 review and the corresponding values for the 2000 review. To do this, we estimated the standard errors for the third quartiles. These were calculated using the method based on the kernel density, as described by the US National Institute of Standards and Technology [17]. The third quartile values were taken to be significantly different (at the 68% confidence level) if the absolute difference in the third quartiles between 2000 and 2005 was larger than the square root of the sum of the squared standard errors, and at the 95% confidence level if the absolute difference in the third quartiles between 2000 and 2005 was larger than twice the square root of the sum of the squared standard errors. There were 36 adult reference doses (ESD or DAP) for non-dental examinations, for which there were sufficient data to make a comparison between the 2000 and 2005 reviews. For 11 of the reference doses (31%), there was a 95% confidence that they were significantly different for the two reviews. For 15 of the reference doses (42%), there was a 68% confidence that they were different for the two reviews. Thus, in the majority of cases (73%), it The British Journal of Radiology, January

10 D Hart, M C Hillier and B F Wall Table 5. National reference doses for dental radiography 2005 review Radiograph Reference dose No. of X-ray sets Absorbed dose to air (mgy) Intra-oral (adult) Intra-oral (child) DWP per radiograph (mgy mm) Panoramic (adult and child) DAP per radiograph (mgy cm 2 ) Panoramic (adult and child) DWP, dose width product; DAP, dose area product. was considered reasonable to update the DRL by using the 2005 third quartile values. For the remaining 10 cases. there was no clear statistical difference between the 2000 and 2005 third quartiles. These 10 cases are listed below in Table 6 with the suggested approach for choosing a DRL. For the first two cases, the third quartiles are the same for both reviews, and so the DRL can remain unchanged. For the other eight cases, it is suggested that, if both the number of rooms and the number of patients is smaller for 2005, the old 2000 reference doses should be retained as DRLs whereas, if the number of rooms or number of patients is larger, the DRL should be updated to the 2005 value. It was not possible to calculate the standard error on the third quartiles for the dental examinations, as we did not have access to the original data from the 1990s. For paediatric medical examinations, the sample size (in terms of the number of rooms) for the 2000 review is much smaller than for the 2005 review; therefore, the reference doses from the latter should be preferred. International comparison of DRLs Table 7 lists some of the suggested DRLs for the UK alongside comparable DRLs for other nations. As a result of the European Communities Medical Exposure Directive [26], all member states of the European Union are required to promote the establishment and use of DRLs having regard to European DRLs where available. DRLs, therefore, have a legal status in the European Union, which is not necessarily the case elsewhere (e.g. Norway, Switzerland and the USA). For the USA and several European countries, we have listed what we believe are the current national DRLs endorsed by the appropriate regulatory authority. The table indicates our understanding of the situation in early 2008, but it is not claimed to be comprehensive or absolutely correct, as the DRLs may have changed after our enquiries were made. The UK values are mostly lower (and sometimes substantially lower) than those for other nations. In the table, there are a number of identical DRLs for ESDs/ radiographs for France, Germany, Italy, Spain and Switzerland; these correspond to the criteria for radiation dose to the patient given in the European Guidelines on Quality Criteria for Diagnostic Radiographic Images [27] published in 1996, which are taken by many to be a key source of European DRLs. These criteria for radiation dose were in turn based on the third quartiles found in the UK survey carried out in the mid-1980s [13]. The German DRL for thoracic spine AP is also equal to the third quartile found in the UK 1980s survey. Clearly, a considerable number of these tabulated DRLs are based on old data. The Swiss DRLs for fluoroscopic examinations were the result of a recent survey carried out in However, all of these Swiss DRLs are very much higher than those currently proposed for the UK. The US DRLs were set by the American Association of Physicists in Medicine in 2005 and are based on the 80th percentile of a NEXT (Nationwide Evaluation of X-ray Trends) survey for ; they are based on entrance skin exposure in air without backscatter measured using a standard phantom. The US DRLs do not include DAP values, as DAP meters are not widely used in the USA [28]. Norway has the same DRLs as listed here for Sweden. Table 6. Suggested national DRLs 2005 sample size compared with 2000 Suggested national DRL Rooms Patients ESD/radiograph Lumbar spine LSJ Smaller Smaller 26 mgy (same for both reviews) DAP/radiograph Lumbar spine AP Larger Larger 1.6 Gy cm 2 (same for both reviews) Lumbar spine LSJ Smaller Twice 2.6 Gy cm2 as in 2005 review DAP/exam or procedure Barium follow through Larger Larger 12 Gy cm 2 as in 2005 review Barium meal Smaller Smaller 13 Gy cm 2 as in 2000 review Coronary angiography Larger Larger 29 Gy cm 2 as in 2005 review Femoral angiography Smaller Smaller 33 Gy cm 2 as in 2000 review Nephrostography Same Larger 12 Gy cm 2 as in 2005 review Biliary drainage/interven Smaller Larger 50 Gy cm 2 as in 2005 review Oesophageal dilation Larger Smaller 11 Gy cm 2 as in 2005 review DRL, diagnostic reference level; ESD, entrance surface dose; DAP, dose area product, AP, anteroposterior; LSJ, lumbosacral joint. 10 The British Journal of Radiology, January 2009

11 Commentary: National reference doses for the UK Table 7. A comparison between proposed UK DRLs and national DRLs from different countries UK France Germany Italy Spain Sweden Switzerland USA Date of setting DRLs 2004 [18] 2003 [19] 2000 [20] 1999 [21] 2002 [22] 2006 [23,24] 2005 [25] ADULT Radiograph ESD per radiograph (mgy) Abdomen AP Chest LAT Chest PA Lumbar spine AP Lumbar spine LAT Lumbar spine LSJ Pelvis AP Skull AP/PA Skull LAT Thoracic spine AP 4 7 Thoracic spine LAT 7 12 Dental intra-oral (excludes back scatter) Radiograph DAP per radiograph (Gy cm 2 ) Pelvis AP Examination DAP per examination (Gy cm 2 ) Barium enema Barium follow through Barium meal Coronary angiography Femoral angiography IVU Venography PAEDIATRIC Examination/standard age (years) DAP per examination (Gy cm 2 ) MCU DRL, diagnostic reference levels; ESD, entrance surface dose; AP, anteroposterior; PA, posteroanterior; DAP, dose area product; LAT, lateral; LSJ, lumbosacral joint; MCU, micturating cystourethrogaphy; IVU, intravenous urography. In summary, the US DRLs and the German paediatric DRLs are fairly similar to those proposed for the UK. Most of the other DRLs are based on the European Community quality criteria and are approximately a factor of two higher than the UK 2005 values. All of the proposed UK DRLs are the lowest DRLs amongst the countries listed (in two cases, joint lowest with the USA). Conclusions Patient dose data have been collected for the period for 316 hospitals of all sizes from all over the UK. Approximately dose measurements for hospital X-ray examinations were analysed for the 2005 review, compared with about doses in the 2000 review. In addition, dose measurements on over 8000 dental X-ray sets were analysed. Further reductions in patient doses for most examinations are evident in comparison with previous reviews. No clear evidence could be found for the use of digital imaging equipment having a significant effect on dose. This article presents new and updated national reference doses. For medical procedures, these are expressed in terms of ESD, DAP or fluoroscopy time. For dental X-ray examinations, national reference doses have been expressed in terms of the absorbed dose to air at the end of the spacer/collimator for intra-oral radiographs, and DWP and DAP for panoramic radiographs. The latest reference doses are on average,16% lower than the reference doses for the 2000 review (for about threequarters of these, the differences are statistically significant) and have more than halved over the past 20 years [27]. This Commentary suggests that two of the national reference doses from the 2000 review be retained as DRLs because the older sample size was larger than for the 2005 review. The proposed DRLs in the UK are substantially lower than corresponding national DRLs in other countries. However, there are still high-dose tails to the dose distributions for some common radiographs and examinations, indicating that there is further scope for patient dose reduction. National reference doses will, therefore, still be useful for identifying those hospitals and X-ray rooms with the greatest opportunities for patient dose optimization. The British Journal of Radiology, January

12 D Hart, M C Hillier and B F Wall The next review of the NPDD should contain much more data on digital imaging systems because they will probably have largely replaced film-screen systems by For paediatric radiographs, such as abdomen AP, chest AP/PA, pelvis AP, skull AP and skull lateral, it wouldbeusefultohavemoredosedatatogetherwith information on patient size (both the height and weight, or the thickness of the body part being X-rayed). The collection of such paediatric data might make a suitable undergraduate project for student radiographers. It would also be helpful to receive more detailed information on the complexity and anatomical location of common interventional and angiographic procedures performed on adult patients so that reference doses can be established for precisely specified procedures (e.g. PTCA on one, two or three arteries). The authors would be pleased to receive data for the 2010 review at any time over the next 2 years; please send data to david.hart@hpa.org.uk. Acknowledgments We wish to thank those hospital physicists and radiology department staff who supplied patient dose data; without their help, this article would not have been possible. We also thank our colleagues Jan Jansen and Paul Shrimpton for their comments on this article. References 1. IPSM (1992). Dosimetry Working Party of the Institute of Physical Sciences in Medicine. National protocol for patient dose measurements in diagnostic radiology. Chilton, UK: NRPB. 2. Hart D, Hillier MC, Wall BF, Shrimpton PC, Bungay D. Doses to patients from medical X-ray examinations in the UK 1995 review. Chilton, UK: NRPB, 1996: NRPB-R Hart D, Hillier MC, Wall BF. Doses to patients from medical X-ray examinations in the UK 2000 review. Chilton, UK. NRPB, 2002: NRPB W Hart D, Hillier MC, Wall BF. Doses to patients from radiographic and fluoroscopic X-ray imaging procedures in the UK 2005 review. Chilton UK: 2007: HPA-RPD Department of Health (2000). The Ionising Radiation (Medical Exposure) Regulations 2000 (together with notes on good practice). Available from: Publicationsandstatistics/Publications/PublicationsPolicy AndGuidance/DH_ [Accessed 12 November 2008]. 6. IPEM (2004). Guidance on the establishment and use of diagnostic reference levels for medical X-ray examinations. York, UK: Institute of Physics and Engineering in Medicine: Report Department of Health (2007). Guidance on the establishment and use of diagnostic reference levels (DRLs). Available from: Publications/PublicationsPolicyAndGuidance/DH_ [Accessed 26 September 2008]. 8. Shrimpton PC, Hillier MC, Lewis MA, Dunn M. Doses from computed tomography examinations in the UK review. Chilton, UK: NRPB, 2005: NRPB W Shrimpton PC, Hillier MC, Lewis MA, Dunn M. 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