1.Full

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 RadiationProtection Division of the Health Protection Agency. The latest review of the databaseanalysed the data collected from 316 hospitals over a 5-year period to the end of 2005.The information supplied amounted to a total of 23 000 entrance surface dosemeasurements and 57 000 dose–area product measurements for single radiographs,and 208 000 dose–area product measurements along with 187 000 fluoroscopy timesfor diagnostic examinations or interventional procedures. In addition, patient dosedata 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 dosedistributions for 30 types of diagnostic X-ray examination and 8 types of interventionalprocedure on adults, and for 4 types of X-ray examination on children. The referencedoses 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 nationalreference doses that were derived from a survey in the mid-1980s. This commentarysuggests that two of the national reference doses from the 2000 review be retained asdiagnostic reference levels because the older sample size was larger than for the 2005review. No clear evidence could be found for the use of digital imaging equipmenthaving a significant effect on dose.

Received 2 May 2008Revised 7 July 2008Accepted 15 July 2008

DOI: 10.1259/bjr/12568539

’ 2009 The British Institute of

Radiology

The National Patient Dose Database (NPDD) wasestablished in 1992 by the National RadiologicalProtection Board (NRPB) after the publication of aNational Protocol for Patient Dose Measurements inDiagnostic Radiology [1]. The purpose of the NPDD wasto collate the measurements of radiation doses to patientsfrom common radiographic and fluoroscopic X-rayexaminations carried out in hospitals throughout theUK, and to monitor any trends.

The NRPB was merged into the Health ProtectionAgency in April 2005, as its Radiation ProtectionDivision (RPD). The RPD is responsible for maintainingthe NPDD, and will continue to publish reviewsrecommending national reference doses approximatelyevery 5 years. Three reviews of the data have beenpublished for each of the 5-year periods preceding 1995,2000 and 2005 [2–4]. The latest review [4] was publishedin August 2007. A total of more than 700 hospitals andclinics have contributed data to one or more of thesereviews.

The Ionising Radiation (Medical Exposure)Regulations 2000 [5] (IR(ME)R) introduced a legalframework for the establishment of ‘‘diagnostic referencelevels’’ (DRLs) in the UK. Guidance on the establishment

and use of DRLs for medical and dental X-ray examina-tions was prepared by a joint working party of relevantprofessional bodies and published by the Institute ofPhysics and Engineering in Medicine (IPEM) in 2004 [6].This guidance recommended that the national referencedoses published in the 5-yearly reviews of the NPDD bea major source for national DRLs. Indeed, in April 2007,the English Department of Health formally adopted [7]the national reference doses recommended in the 2000review of the NPDD as national DRLs for radiographicand fluoroscopic X-ray examinations in compliance withIR(ME)R. This article discusses the subsequent 2005review of the NPDD, presents the latest nationalreference doses, and discusses their potential impact onfuture revisions of the national DRLs by the Departmentof Health.

Radiation doses from dental X-ray examinations havebeen included for the first time in the latest 5-yearlyreview. Dental practices usually have limited access toradiation protection expertise, and national referencedoses can be an important aid to the optimization ofpatient doses in these circumstances. It is intended thatnational reference doses for dental X-ray examinationswill be included in future reviews of the NPDD.

Radiation doses to patients from CT examinations arenot included in the NPDD. Such information is stored ina separate database, also maintained by the RPD, calledPREDICT (Patient Radiation Exposure and Dose In CT).

Address correspondence to: D Hart, Radiation Protection Division,Health Protection Agency, Chilton, Didcot, Oxon OX11 0RQ, UK. E-mail: [email protected]

The British Journal of Radiology, 82 (2009), 1–12

The British Journal of Radiology, January 2009 1

It is intended that the data in PREDICT will be reviewedat regular intervals in a similar manner to NPDD. Thelatest review of the PREDICT database includes nationalreference doses for eight common types of CT examina-tion and was performed for the year 2003 [8, 9]. TheDepartment of Health has also formally adopted [7]these reference doses as national DRLs in compliancewith 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 fluoroscopytimes, taken according to the National Protocol [1].

2. Dental radiographs and examinations. These mea-surements included the absorbed dose to air at the tipof the collimator for intra-oral radiographs, and thedose–width product (DWP, i.e. the dose multiplied bythe beam width as measured at the post-patientcollimator) and DAP for panoramic radiographs,taken according to IPEM guidance [6].

In addition to dose measurements, data were collectedon the patient (e.g. age, sex and weight, but not identity),the radiological equipment used and the examinationtechnique (see Appendix B of [4]). 97% of the dosemeasurements for the 5-year period to 2005 related tonon-dental examinations and were supplied by hospitalphysicists, radiographers and radiologists from through-out the UK. 1% of the data came from the RPD’s PatientDosimetry Service, which used thermoluminescent dose-meters to measure ESDs for simple radiographic exam-inations performed in hospitals. Doses from dentalpractices constituted the rest of the data (2%). More thantwo-thirds of the dental dose measurements came fromthe Dental X-ray Protection Service (DXPS) of the RPD[10]. The remainder was supplied by seven medicalphysicists who provide radiation protection advice todentists.

For most X-ray examinations, patient doses increasewith patient size. To circumvent this variation, the datawere analysed in terms of the mean patient dose for aspecific examination within a specific room. TheNational Protocol for Patient Dose Measurements inDiagnostic Radiology recommends that the meanweight of a sample of patients in a specific room shouldlie in the range 65–75 kg for the mean dose to beindicative of the typical dose to an average (70 kg) adultpatient. Not all data providers followed this recommen-dation when submitting data to the NPDD, and manydid not supply any information on patient weight.Consequently, dose data for adult patients were onlyincluded in this review if the mean patient weight wasin the range 65–75 kg, or if the patient weight wasunspecified but there was a minimum of 10 patients perroom. These are the same selection criteria as used inthe 2000 review [3] and resulted in rejection of ,20% ofthe data supplied.

Approximately 4% of all the dose measurements in thelatest database relate to children. For medical X-ray

examinations, a method has been developed previously[11] for adjusting doses measured in children of any ageto derive the dose that would have been given to thenearest standard-sized patient representing a 0-, 1-, 5-,10- or 15-year-old child. This method was applied to thelimited amount of data from paediatric patients in theNPDD, where the required information on the thicknessof the body part being X-rayed, or the height and weightof the patient, was included.

For dental X-ray examinations, a single dose measure-ment is made on each dental radiograph set using typicalexposure conditions for an adult or a child, but without apatient present. There is therefore no need to select thedata on the basis of patient size.

Results

For hospital X-ray examinations, 23 000 ESD measure-ments, 57 000 DAP measurements for single radio-graphs, and 208 000 DAP measurements along with187 000 fluoroscopy times for complete diagnosticexaminations or interventional procedures were storedin the database before data selection criteria wereapplied. The data came from 316 hospitals from allregions of the UK, from all sizes of hospital, and fromboth the NHS and the independent sector. This samplecovers ,23% of all hospitals and clinics with diagnosticX-ray facilities in the UK.

The dental X-ray data came from approximately 3000dental clinics in all regions of the UK (i.e. about 25% of alldental clinics in the UK [12]) and consisted of:

1. more than 6000 measurements of the absorbed dose toair at the tip of the collimator for intra-oral radio-graphs;

2. over 2200 measurements of DWP and nearly 2000measurements of DAP for panoramic radiographs.

Figure 1 compares the 2005 review histograms of roommean ESDs for several common radiographs withcorresponding histograms from the 1995 and 2000reviews. The third quartiles of the room mean ESDvalues are indicated by a vertical line on the histograms,and it can be seen that they have become progressivelylower with each review for most radiographs. It can alsobe seen that the high-dose tails of the distributions havelargely decreased over the years and the distributionshave become slightly narrower, but not as much as mightbe expected if all hospitals exceeding the reference doseshad taken corrective action.

Figure 2 compares the histograms of the room meanDAP values for four barium studies over the threereviews: 1995, 2000 and 2005. The third quartile valueshave in general decreased slightly over the three reviews,but the high-dose tails do not show much indication ofshortening.

Figures 3 and 4 compare the third quartile values over10-year intervals since the original survey in 1985 [13] forthose radiographs and examinations with sufficient data.It can be seen that the third quartiles have steadilydecreased.

For hospital X-ray examinations, a comparison wasmade between the doses from digital systems (i.e.

D Hart, M C Hillier and B F Wall

2 The British Journal of Radiology, January 2009

Figure 1. Comparison of room mean entrance surface dose (ESD) distributions for all three reviews. AP, anteroposterior; LAT,lateral; LSJ, lumbosacral joint; PA, posteroanterior.

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-teston the ESD for 10 common types of radiograph showedthat the mean ESD for CR was significantly different atthe 98% confidence level to that for film for four types ofradiograph 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-testshowed that the mean CR dose was not significantlydifferent to that for film for each of the 10 types ofradiograph. For flat-panel detectors, which were mainlyused in cardiac catheterization laboratories, a similarcomparison with conventional systems (i.e. those notinvolving CR or flat-panel detectors) for eight proce-dures indicated no significant difference in the meanDAP 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 mindthat 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, nationalreference doses for common X-ray examinations arebased on third quartile values of the mean patient dosesobserved in a nationally representative sample of X-rayrooms. Reference doses set at this level provide anindication of when the imaging equipment or examina-

tion techniques used in a particular X-ray room areproducing unusually high doses and, if exceeded, shouldlead to further investigation and corrective action. Theyalso provide a major source of data for consideration bythe Department of Health when formally adoptingnational diagnostic reference levels in accordance withIR(ME)R, as discussed earlier.

Adult patientsOn the assumption that a minimum of about 20 rooms

is necessary (as adopted in the previous reviews), thereare sufficient data on both ESD and DAP per radiographin the 2005 review to recommend reference doses interms of both these quantities for the 11 types ofradiograph shown in Table 1. The reference doses aregiven to two significant figures. The number of roomssupplying data for each radiograph is also indicated inthe table (and for each subsequent table of nationalreference doses for non-dental examinations).

The latest set of national reference doses for 17 types ofcomplete diagnostic examination, in terms of both thetotal DAP and the total fluoroscopy time for theexamination, is shown in Table 2. As in the previousreview, water-soluble enemas and swallows have beencombined with barium enemas and swallows and giventhe same reference doses as in Table 2, as the respectiveDAP values and fluoroscopy times are similar for theseexaminations when performed with the two types ofcontrast media. As was found in the previous review, the

Figure 1. Continued.



mean weight of coronary angiography patients wasabove the normal selection range (65–75 kg). A range of75–85 kg was therefore used for this examination inorder to maximize the sample of patients. (The 75–85 kgrange was also used for percutaneous transluminalcoronary angioplasties (PTCAs), as shown in Table 3.)

Table 3 shows the latest set of national reference dosesfor eight interventional procedures, in terms of both totalDAP and total fluoroscopy time. Biliary drainage andbiliary intervention procedures have been combined inTable 3, as the respective DAP values and fluoroscopytimes were very similar for both types of procedure.

Figure 2. Comparison of room mean dose–area product (DAP) distributions for all three reviews.



Biliary interventions and PTCAs have the highestreference dose (50 Gy cm2) of all the procedures andexaminations listed in Tables 2 and 3.

The national reference doses in Tables 1–3 are, ingeneral, slightly lower than or equal to the correspond-ing 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 spineanteroposterior (AP) (14%), the DAP/examination forbarium meals (8%), femoral angiography (9%), sialogra-phy (25%) and venography (40%), and the fluoroscopytimes for femoral angiography (10%), nephrostography(4%) and sialography (6%). (For barium meals andfemoral angiography, the sample sizes were smaller

Figure 3. Third quartiles for entrance surface dose (ESD) for radiographs. AP, anteroposterior; LAT, lateral; LSJ, lumbosacraljoint; PA, posteroanterior.

Figure 4. Third quartiles for dose–area product (DAP) per examination. IVU, intravenous urography.



than for the 2000 review. An analysis later in thisCommentary (see Table 6) indicates that the apparentincreases for these two examinations may not bereliable.)

Paediatric patientsAs in the 2000 review, there were only three medical

X-ray examinations on children where sufficient data onpatient size were available to estimate doses for each ofthe five standard sizes from at least 20 rooms. Table 4shows the national paediatric reference doses based onthe third quartiles of room mean DAP for these threeexaminations at each standard age corresponding to thestandard size.

The third quartile values of the doses for the 1-year-oldand 5-year-old standard-sized patients differ onlyslightly between all three examinations (as was foundin the 2000 review). It is therefore recommended that thesame reference dose be used for both ages, and the valueis shown in brackets in Table 4.

Doses to 15-year-olds for micturating cystourethroga-phy, barium meals and barium swallows are a factor of

2.5–5 times lower than those to adults. Therefore, there isa need (as in the previous review) to have separatereference 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 the2000 review. The only exception to this is a bariumswallow for a 10-year-old, which is now slightly higher.It may be noted that these national reference doses arehigher by a factor of 4–10 than the local DRLs in use atthe Great Ormond Street Hospital for Sick Children in2004 [14]. Although paediatric dose data from thathospital were supplied for this review, it did not includethe information on patient size that is necessary forderiving the ‘‘standard age’’ doses shown in Table 4 [11].The low patient doses reported from Great OrmondStreet Hospital demonstrate what is possible whenpaediatric radiography is fully optimized by dedicatedpaediatric staff.

Dental radiographyIn 1999, Napier [15] presented reference doses for

dental radiography based on a survey of over 6000 intra-

Table 1. National reference doses for individual radiographs on adult patients — 2005 review

Radiograph ESD per radiograph(mGy)

No. of rooms DAP per radiograph(Gy cm2)

No. of rooms

Abdomen AP 4.2 209 2.6 127Chest LAT 0.55 39 0.31 23Chest PA 0.14 311 0.11 210Lumbar spine AP 5.1 237 1.6 118Lumbar spine LAT 11 232 2.5 120Lumbar spine LSJ 26 27 2.6 25Pelvis AP 3.7 231 2.1 150Skull AP/PA 2.0 42 0.78 20Skull LAT 1.3 26 0.49 19Thoracic spine AP 4.1 79 0.93 36Thoracic spine LAT 7.1 79 1.4 27

ESD, entrance surface dose; DAP, dose–area product; AP, anteroposterior; LAT, lateral; LSJ, lumbosacral joint; PA,posteroanterior.

Table 2. National reference doses for diagnostic examinations on adult patients — 2005 review

Examination DAP per exam(Gy cm2)

No. of rooms Fluoroscopy time perexam (min)

No. of rooms

Barium (or water-soluble) enema 24 269 2.8 233Barium follow through 12 97 2.2 90Barium meal 14 104 2.7 99Barium meal and swallow 11 75 2.2 75Barium (or water-soluble) swallow 9.0 173 2.3 159Coronary angiographya 29 110 4.5 101Femoral angiography 36 52 5.5 14Fistulography 13 22 3.8 20Hysterosalpingography 2.9 71 0.95 68IVU 14 35 - -MCU 12 28 1.9 28Nephrostography 12 35 4.8 34Sialography 2.0 20 1.7 20Sinography 8.5 39 2.1 39Small bowel enema 40 37 9.2 34T-tube cholangiography 7.9 37 1.9 37Venography 7.5 27 2.2 26

DAP, dose–area product; IVU, intravenous urography; MCU, micturating cystourethrogaphy.a75–85 kg.



oral X-ray sets and nearly 400 panoramic X-ray sets bythe NRPB Dental X-ray Protection Service between 1995and 1998. The recommended national reference doseswere 4 mGy for adult intra-oral radiography and65 mGy mm DWP for adult panoramic radiography.IPEM Report 91 based its remedial levels for patientdoses in dental radiography on Napier’s nationalreference doses [16].

National reference doses for dental radiography havenot previously been included in the reviews of theNPDD, but were presented for the first time in the 2005review. They are shown in Table 5, and are based on thethird quartiles of the dose distributions seen in a sampleof ,3000 dental clinics throughout the UK. The numberof dental X-ray sets on which measurements were madeis indicated in Table 5.

The new adult reference dose for intra-oral radio-graphs (2.3 mGy) is ,40% lower than the 1999 value(4 mGy), probably owing to the use of faster film-screenand digital systems. This is the first time that a nationalreference dose for intra-oral radiographs on children hasbeen recommended (1.5 mGy), and it is ,35% lowerthan the corresponding adult value.

Doses for panoramic radiographs on adults andchildren were found to be very similar, so it was not

considered necessary to have separate national referencedoses for these two types of patient. The national referencedoses for panoramic radiographs shown in Table 5 areexpressed in terms of both DWP and DAP, and apply toboth adults and children. The new DWP reference dose forpanoramic radiography is only ,10% lower than the 1999reference dose. There are advantages in expressing thereference dose for panoramic radiography in terms ofDAP rather than DWP. It is more consistent with theapproach adopted for medical X-ray examinations and ismore closely related to patient dose, as the DAP measuredat the post-patient collimator (in the absence of the patient)is, to a first approximation, the same as the DAP measuredat the patient’s entrance surface. DAP values can bederived from the DXPS data, as the height as well as thewidth of the X-ray beam is measured in the DXPS postalservice. DAP is consequently likely to become thepreferred patient dose quantity for panoramic dentalradiography in the future [6].

Discussion

Consideration will need to be given as to whichreference doses should be formally adopted as nationalDRLs in accordance with IR(ME)R. When consideringthis issue, it is relevant to examine whether there is asignificant difference between the third quartiles for the2005 review and the corresponding values for the 2000review. To do this, we estimated the standard errors forthe third quartiles. These were calculated using themethod based on the kernel density, as described by theUS National Institute of Standards and Technology [17].The third quartile values were taken to be significantlydifferent (at the 68% confidence level) if the absolutedifference in the third quartiles between 2000 and 2005was larger than the square root of the sum of the squaredstandard errors, and at the 95% confidence level if theabsolute difference in the third quartiles between 2000and 2005 was larger than twice the square root of thesum of the squared standard errors.

There were 36 adult reference doses (ESD or DAP) fornon-dental examinations, for which there were sufficientdata to make a comparison between the 2000 and 2005reviews. For 11 of the reference doses (31%), there was a95% confidence that they were significantly different forthe two reviews. For 15 of the reference doses (42%),there was a 68% confidence that they were different forthe two reviews. Thus, in the majority of cases (73%), it

Table 3. National reference doses for interventional procedures on adult patients — 2005 review

Interventional procedure DAP per exam(Gy cm2)

No. of rooms Fluoroscopy time perexam (min)

No. of rooms

Biliary drainage/intervention 50 39 15 38Facet joint injection 5.2 23 1.8 20Hickman line 3.0 47 1.4 43Nephrostomy 14 30 5.1 28Oesophageal dilation 11 22 2.8 22Oesophageal stent 25 24 5.9 22Pacemaker 11 45 8.2 45PTCA (single stent)a 50 28 13 26

DAP, dose–area product; PTCA, percutaneous transluminal coronary angiography.a75–85 kg.

Table 4. National reference doses for diagnostic examina-tions on paediatric patients — 2005 review

Examination Standardage (year)

DAP perexamination(Gy cm2)

No. of rooms

MCU 0 0.3 531 0.7 (0.8) 595 0.8 (0.8) 58

10 1.5 4415 2.5 30

Barium meal 0 0.4 161 1.1 (1.2) 255 1.3 (1.2) 20

10 2.4 2215 6.4 25

Barium swallow 0 0.4 261 1.2 (1.3) 405 1.3 (1.3) 36

10 2.9 4115 3.5 40

Valuesinbracketsareforthecombined1–5yearsagegroup.DAP,dose–area product; MCU, micturating cystourethography.



was considered reasonable to update the DRL by usingthe 2005 third quartile values. For the remaining 10 cases.there was no clear statistical difference between the 2000and 2005 third quartiles. These 10 cases are listed belowin Table 6 with the suggested approach for choosing aDRL. For the first two cases, the third quartiles are thesame for both reviews, and so the DRL can remainunchanged. For the other eight cases, it is suggested that,if both the number of rooms and the number of patientsis smaller for 2005, the old 2000 reference doses shouldbe retained as DRLs whereas, if the number of rooms ornumber of patients is larger, the DRL should be updatedto the 2005 value.

It was not possible to calculate the standard error onthe third quartiles for the dental examinations, as we didnot have access to the original data from the 1990s. Forpaediatric medical examinations, the sample size (interms of the number of rooms) for the 2000 review ismuch smaller than for the 2005 review; therefore, thereference doses from the latter should be preferred.

International comparison of DRLs

Table 7 lists some of the suggested DRLs for the UKalongside comparable DRLs for other nations. As a resultof the European Communities Medical ExposureDirective [26], all member states of the European Unionare required to ‘‘promote the establishment and use ofDRLs…having regard to European DRLs where available’’.DRLs, therefore, have a legal status in the EuropeanUnion, 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 webelieve are the current national DRLs endorsed by theappropriate regulatory authority. The table indicates ourunderstanding of the situation in early 2008, but it is notclaimed to be comprehensive or absolutely correct, as theDRLs may have changed after our enquiries were made.

The UK values are mostly lower (and sometimessubstantially lower) than those for other nations. In thetable, there are a number of identical DRLs for ESDs/radiographs for France, Germany, Italy, Spain andSwitzerland; these correspond to the criteria for radiationdose to the patient given in the European Guidelines onQuality Criteria for Diagnostic Radiographic Images [27]published in 1996, which are taken by many to be a keysource of ‘‘European DRLs’’. These criteria for radiationdose were in turn based on the third quartiles found inthe UK survey carried out in the mid-1980s [13]. TheGerman DRL for thoracic spine AP is also equal to thethird quartile found in the UK 1980s survey. Clearly, aconsiderable number of these tabulated DRLs are basedon old data. The Swiss DRLs for fluoroscopic examina-tions were the result of a recent survey carried out in2002–2004. However, all of these Swiss DRLs are verymuch higher than those currently proposed for the UK.The US DRLs were set by the American Association ofPhysicists in Medicine in 2005 and are based on the 80thpercentile of a NEXT (Nationwide Evaluation of X-rayTrends) survey for 1990–1994; they are based on entranceskin exposure in air without backscatter measured usinga standard phantom. The US DRLs do not include DAPvalues, as DAP meters are not widely used in the USA[28]. Norway has the same DRLs as listed here forSweden.

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) 2.3 6170Intra-oral (child) 1.5 253

DWP per radiograph (mGy mm)Panoramic (adult and child) 60 2175

DAP per radiograph (mGy cm2)Panoramic (adult and child) 82 1910

DWP, dose–width product; DAP, dose–area product.

Table 6. Suggested national DRLs

2005 sample size compared with 2000 Suggested national DRL

Rooms Patients

ESD/radiographLumbar spine LSJ Smaller Smaller 26 mGy (same for both reviews)DAP/radiographLumbar spine AP Larger Larger 1.6 Gy cm2 (same for both reviews)Lumbar spine LSJ Smaller Twice 2.6 Gy cm2 as in 2005 reviewDAP/exam or procedureBarium follow through Larger Larger 12 Gy cm2 as in 2005 reviewBarium meal Smaller Smaller 13 Gy cm2 as in 2000 reviewCoronary angiography Larger Larger 29 Gy cm2 as in 2005 reviewFemoral angiography Smaller Smaller 33 Gy cm2 as in 2000 reviewNephrostography Same Larger 12 Gy cm2 as in 2005 reviewBiliary drainage/interven Smaller Larger 50 Gy cm2 as in 2005 reviewOesophageal dilation Larger Smaller 11 Gy cm2 as in 2005 review

DRL, diagnostic reference level; ESD, entrance surface dose; DAP, dose–area product, AP, anteroposterior; LSJ, lumbosacral joint.



In summary, the US DRLs and the German paediatricDRLs are fairly similar to those proposed for the UK.Most of the other DRLs are based on the EuropeanCommunity quality criteria and are approximately afactor of two higher than the UK 2005 values. All of theproposed UK DRLs are the lowest DRLs amongst thecountries listed (in two cases, joint lowest with the USA).

Conclusions

Patient dose data have been collected for the period2001–2005 for 316 hospitals of all sizes from all over theUK. Approximately 288 000 dose measurements forhospital X-ray examinations were analysed for the 2005review, compared with about 180 000 doses in the 2000review. In addition, dose measurements on over 8000dental X-ray sets were analysed. Further reductions inpatient doses for most examinations are evident incomparison with previous reviews. No clear evidencecould be found for the use of digital imaging equipmenthaving a significant effect on dose.

This article presents new and updated national referencedoses. For medical procedures, these are expressed interms of ESD, DAP or fluoroscopy time. For dental X-rayexaminations, national reference doses have beenexpressed in terms of the absorbed dose to air at the endof the spacer/collimator for intra-oral radiographs, andDWP and DAP for panoramic radiographs. The latestreference doses are on average ,16% lower than thereference doses for the 2000 review (for about three-quarters of these, the differences are statistically significant)and have more than halved over the past 20 years [27]. ThisCommentary suggests that two of the national referencedoses from the 2000 review be retained as DRLs becausethe older sample size was larger than for the 2005 review.The proposed DRLs in the UK are substantially lower thancorresponding national DRLs in other countries. However,there are still high-dose tails to the dose distributions forsome common radiographs and examinations, indicatingthat there is further scope for patient dose reduction.National reference doses will, therefore, still be useful foridentifying those hospitals and X-ray rooms with thegreatest opportunities for patient dose optimization.

Table 7. A comparison between proposed UK DRLs and national DRLs from different countries

UK France Germany Italy Spain Sweden Switzerland USA

Date of settingDRLs 2004 [18] 2003 [19] 2000 [20] 1999 [21] 2002 [22] 2006 [23,24] 2005 [25]

ADULTRadiograph ESD per radiograph (mGy)Abdomen AP 4 10 10 10 10 4.5Chest LAT 0.6 1.5 1.5 1.5 1.5 1.5Chest PA 0.15 0.3 0.3 0.4 0.3 0.3 0.25Lumbar spine AP 5 10 10 10 10 10 5Lumbar spine LAT 11 30 30 30 30 30Lumbar spine LSJ 26 40 40 40Pelvis AP 4 10 10 10 10 10Skull AP/PA 2 5 5 5 5 5Skull LAT 1.3 3 3 3 3 3Thoracic spine AP 4 7Thoracic spine LAT 7 12Dental intra-oral

(excludes backscatter) 2.3 7 2.3

Radiograph DAP per radiograph (Gy cm2)Pelvis AP 2.1 4Examination DAP per examination (Gy cm2)Barium enema 24 70 50 150Barium follow

through 12 70Barium meal 13 60Coronary

angiography 29 60 80 80Femoral

angiography33 85 210

IVU 14 20 35Venography 7.5 9PAEDIATRICExamination/stan-

dard age (years)DAP per examination (Gy cm2)

MCU 0 0.3 0.61 0.8 0.95 0.8 1.210 1.5 2.415 2.5

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.



The next review of the NPDD should contain muchmore data on digital imaging systems because they willprobably have largely replaced film-screen systems by2010. For paediatric radiographs, such as abdomen AP,chest AP/PA, pelvis AP, skull AP and skull lateral, itwould be useful to have more dose data together withinformation on patient size (both the height and weight, orthe thickness of the body part being X-rayed). Thecollection of such paediatric data might make a suitableundergraduate project for student radiographers. It wouldalso be helpful to receive more detailed information on thecomplexity and anatomical location of common interven-tional and angiographic procedures performed on adultpatients so that reference doses can be established forprecisely specified procedures (e.g. PTCA on one, two orthree arteries). The authors would be pleased to receivedata for the 2010 review at any time over the next 2 years;please send data to [email protected].

Acknowledgments

We wish to thank those hospital physicists andradiology department staff who supplied patient dosedata; without their help, this article would not have beenpossible. We also thank our colleagues Jan Jansen andPaul Shrimpton for their comments on this article.

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npdd national reference

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