diagnostic reference levels: concept, misconceptions ...

REVIEW ARTICLE

DIAGNOSTIC REFERENCE LEVELS: CONCEPT, MISCONCEPTIONS AND CURRENT TRENDS-A REVIEW Flavious Bobuin Nkubli, Christian Chukwuemeka Nzotta, Joseph Dlama Zira De partm e ntofMe dicalRadiograph y, Col l e ge ofM e dicalScie nce s , Unive rs ity ofM aiduguri, Maiduguri, Borno State , Nige ria. PJR January - March 2018; 28(1): 45-49

ABSTRACT Th e conce pt of diagnos tic re fe re nce l e ve lh as be e n in e xis te nce for al m os t th re e de cade s . Ith as al s o found its pl ace in re gul atory s ys te m s for ne arl y 20 ye ars . Curre ntl y, nationalbodie s are e xpe cte d to e s tabl is h th e ir diagnos tic re fe re nce l e ve lval ue s . Th e re is al s o provis ion for l ocaland re gionaldiagnos tic re fe re nce l e ve l s . Al s o, al m os t al l re gul atory s ys te m s incl ude th e us e of diagnos tic re fe re nce l e ve l s for patie ntprote ction as an optim iz ation tool . De s pite th e fore going, th e re is s til la l ack ofk now l e dge ofth e conce ptw ith in th e m e dicalcom m unity. Th is prom pte d th e Inte rnationalCom m is s ion on Radiol ogicalProte ction (ICRP) to re vie w its curre nt docum e nt on diagnos tic re fe re nce l e ve lw ith a vie w to com e up w ith a ne w one cons is te nt w ith curre nt te ch nol ogy and practice . Th is pape r s e e k s to re vie w th e conce pt, m is conce ptions and curre nttre nds in diagnos tic re fe re nce l e ve lw ith s pe cial focus on s om e re vis e d s e ction in th e ne w (ICRP) docum e nt.

Introduction It is norm alfor a patie nt unde rgoing a radiol ogic e xam ination invol ving th e us e ofionis ing radiation to e xpe ct th at th e radiation dos e re ce ive d in diffe re nt h os pital s for th e s am e proce dure w il lbe w ith in a narrow range . H ow e ve r, s e ve rale m piricals urve ys s h ow th at th is is not al w ays th e cas e . 1,2,3 Dos e variations by a factor of20 or m ore h ave be e n re porte d for radiograph ic e xam inations in th e e arl y and l ate 19 80’s both in th e Unite d K ingdom and Europe an Union. Diagnos tic re fe re nce l e ve l s (DRLs ) h ave prove d us e fulas a toolin s upport ofdos e auditand practice re vie w for prom oting im prove m e nts in patie nt prote ction 3. Th e appl ication ofDRLs in th e UK s ince 19 89 w ith in a coh e re ntfram e w ork h as l e ad to incre as e aw are ne s s ofdos e and h e l pe d to re duce unne ce s s ary x- ray e xpos ure . DRLs w e re firs t im pl e m e nte d in re l ation to conve ntionalradiograph y in th e 19 80’s and s ubs e q ue ntl y de ve l ope d for oth e r im aging m odal itie s in th e 19 9 0.4 DRLs as de fine d by th e curre nt Inte rnationalBas ic

Safe ty Standard (BSS), Ge ne ralSafe ty Re q uire m e nts GSR Part 3 is a l e ve lus e d in m e dicalim aging to indicate w h e th e r in routine conditions th e dos e s to patie nts or th e am ount of radioph arm ace utical adm inis te re d in a s pe cifie d radiol ogicalproce dure for m e dicalim aging is unus ual l y h igh or unus ual l yl ow e DRLs are a us e fultool , for th at proce dure .5 W h il th e y are butonl y one s te p in th e ove ral loptim iz ation e d th e proce s s .6 Se ve ralm is conce ptions h ave trail us e ofDiagnos tic Re fe re nce Le ve l s w ith in th e m e dical im aging com m unity e s pe cial l y in de ve l oping countrie s . Th is re vie w is inte nde d to e xpl ore th e conce pt, m is conce ptions and curre nt tre nds in diagnos tic re fe re nce l e ve l s. CONCEPT OF DIAGNOSTIC REFERENCE LEVELS Th e Inte rnationalCom m is s ion on Radiol ogicalProte ction (ICRP), w h os e re com m e ndations form th e bas is of radiation s afe ty s tandards w orl dw ide , introduce d th e conce pt of DRLs in 19 9 0 and furth e r de ve l ope d

Corre s ponde nce : Dr. Fl avious Bobuin Nk ubl i De partm e ntofM e dicalRadiograph y, Col l e ge ofM e dicalScie nce s , Unive rs ity ofM aiduguri, M aiduguri, Borno State , Nige ria. Em ail : active fl avour@ yah oo.com Subm itte d 2 O ctobe r 2017, Acce pte d 5 De ce m be r 2017

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PJR January - March 2018; 28(1)

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th e conce pt w ith th e guide l ine s in publ ications 73 and 105 and ICRP s upporting guidance 2: s pe cifical l y th e ICRP de fine s a DRLas “a form of inve s tigation l e ve l , appl y to an e as il y m e as ure d q uantity, us ual l y th e abs orbe d dos e in air or e q uival e nt m ate rial at th e s urface ofa s im pl e s tandard ph antom or re pre s e ntative patie nt”.7 DRLs are not dos e l im its . W h e re as dos e l im its are dos e val ue s th atare notto be e xce e de d, DRLs can im its be e xce e de d if cl inicalne e d de m ands .8 Dos e l do notappl y to e xpos ure ofpatie nts (M e dicale xpos ure s ) be caus e th is m ay com prom is e patie nt care . H ow e ve r, dos e l im its are appl icabl e to occupational e xpos ure s . DRLs are us e d as a trigge r l e ve lto ide ntify th os e facil itie s w ith unus ual l y h igh dos e s in a s pe cifie d radiol ogic proce dure , for w h ich optim iz ation actions are ne e de d. In contras tto occupationaldos e l im its , DRLs s h oul d notappl y to individualpatie nts , be caus e one patie nt’s body m as s and h abitus m ay re q uire h igh e r dos e th an th os e ofa s tandard patie nt.4 Type of procedure

Dose quantity and units

Radiography (including dental radiography)

Incident air kerma Ki (in air, without backscatter) or entrance surface air kerma (or dose) Ke (in air with backscatter), in mGy, for a given radiographic projection; air kerma (or dose)-area product in mGy.cm2

Mammography

Incident air kerma (Ki), in mGy; mean glandular dose (DG), in mGy

Complex procedures including fluoroscopy guided procedures

Air kerma (or dose)-area product (PKA), in Gy.cm2cumulative air kerma at the reference point (Ka,r) in Gy

CT

CT air kerma (or dose) index in mGy; CT air kerma (or dose) length product, in mGy.cm

Diagnostic nuclear medicine

Administered activity (A), in MBq

Tabl e 1: Curre ntl y acce pte d re fe re nce dos e q uantitie s according to th e Inte rnationalCom m is s ion on Radiation m e as ure m e nts and Units (ICRU) e xce rpte d from Vas s il e va and Re h ani4 pre s e nte d on Tabl e 1

Standardiz ation of radiation dos e and re duction of variations in dos e w ith outcom prom is ing th e cl inical purpos e of s uch e xam ination or proce dure m ak e s th e ne e d for DRLs im pe rative . Exam ination-s pe cific or proce dure -s pe cific DRLs for various patie ntgroups can provide s tim ul us for m onitoring practice to prom ote im prove m e ntin patie ntprote ction. Itis al s o a us e ful

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toolto prom ote dos e audit.3,4 Itis re com m e nde d th atDRLs be s e tfor re pre s e ntative e xam ination or proce dure s pe rform e d in th e l ocal are a, country or re gion w h e re th e y are appl ie d. DRLs re fl e ctth e typicalpractice in a country or re gion.7,9 ,10 Due to variations in e q uipm e ntand proce dure protocol s be tw e e n diffe re ntfacil itie s in countrie s or re gions , itis a good practice to e s tabl is h nationalor re gional DRLs . Th e gove rnm e nth as a re s pons ibil ity to e ns ure th atDRLs are e s tabl is h e d for th e country.5 H ow e ve r, th e proce s s e s and s te ps tow ards e s tabl is h ing DRLs are l ik e l y to invol ve m any pl aye rs incl uding th e im aging facil itie s , th e h e al th auth oritie s , th e profe s s ionalbodie s and th e re gul atory body.6 Tw o approach e s are adopte d for patie nt dos e m e as ure m e nts and s e tting ofdiagnos tic re fe re nce l e ve l s from radiol ogic proce dure s ;patie nt-bas e d dos im e try and ph antom -bas e d dos im e try.11,12 Th e advantage ofth e us e ofa ph antom is th atonl y one or tw o e xpos ure s w oul d be ne e de d for e ach e xam ination type and e ach radiol ogy facil ity;th e dis advantage is th at itdoe s notre pre s e nta re alcl inicals ituation, and th e s am e s tandard ph antom s h al lbe re q uire d for cons is te ncy. If patie ntdos e m e as ure m e nt is us e d, patie nt s am pl e s h oul d be s e l e cte d to m atch th e m e an body inde xe s (e .g patie ntw e igh tand h e igh tor body m as s inde x [w e igh t in k g /w e igh t2 m ]) to th e pre de fine d “s tandard- s iz e d” patie nt. It is e xpe cte d th at patie nt s am pl e s h oul d be l arge e nough to e ns ure th at th e m e an val ue s re pre s e nt th e typicalpractice in th e facil ity - e .g atl e as t 20 patie nts w ith in a pre de fine d range of body m as s inde xe s . Se parate diagnos tic re fe re nce l e ve l s for pae diatric and adul t patie nts s h oul d be e s tabl is h e d dis tinguis h e d by age body s iz e and w e igh t.12 Es tabl is h m e nt ofDRLs invol ve s four s te ps : Firs t, th e m os tcom m onl y pe rform e d routine diagnos tic e xam inations are ide ntifie d and l e xicons de fine d;for e ach type ofe xam ination, re fe re nce dos e q uantitie s are acce pte d and ide ntifie d and m e as uring m e th od is s tandardis e d. Se cond, in e ach im aging facil ity, dos e m e as ure m e nts are pe rform e d fol l ow ing s tandardis e d m e th od;m e an dos e from patie nts am pl e or ph antom m e as ure m e nt is e s tim ate d for e ach e xam ination and s e tas a typical dos e , us ual l y by m e dicalph ys icis ts . Th ird, typicaldos e s from al lor re pre s e ntative s am pl e


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of facil itie s in th e country or re gion are ce ntral l y anal yz e d;diagnos tic re fe re nce l e ve l s s h oul d be bas e d on dos e s m e as ure d in various type s of h os pital s, cl inics , and practice s re pre s e nting th e typicalpractice in th e country or re gion. Final l y, for diagnos tic radiol ogy, nationaland re gional diagnos tic re fe re nce l e ve l s are us ual l y s e t at 75% pe rce ntil e of th e dis tribution of typicaldos e s for th e s am pl e. Ce rtain e s s e ntialfacts to note about diagnos tic re fe re nce l e ve l s are ; (i) Th e y are notdos e l im its ; (ii) Th e y do not re pre s e nt a borde r be tw e e n good and poor m e dicalpractice ; (iii) Th e y facil itate inve s tigation or are action l e ve l s to ide ntify facil itie s w ith unus ual l y h igh or l ow dos e s (outl ie rs ) w h e re optim iz ation actions ne e d to be appl ie d; (iv) Diagnos tic re fe re nce l e ve l s s h oul d be cons ide re d toge th e r w ith im age q ual ity; (v) Th e y appl y to radiol ogic incl uding nucl e ar m e dicine diagnos tic proce dure s . (vi) DRLs are s pe cifie d for s tandard-s iz e d patie ntor s tandard ph antom ;th e y are give n in e as il y and re producibl y m e as ure d dos e m e trics ; (vii) Th e y s h oul d not be s e t in e ffe ctive dos e ; and th e y are dynam ic val ue s th at s h oul d be re vie w e d pe riodical l y e s pe cial l y as practice and te ch nol ogy ch ange s . M ISCO NCEPTIO NS ABO UT DIAGNO STIC REFERENCE LEVEL Th e conce pt ofdiagnos tic re fe re nce l e ve lh as be e n trail e d by s e ve ralm is conce ptions in practice . Th is is m ore ofa conce rn in de ve l oping countrie s w h e re diagnos tic re fe re nce l e ve l s h ave notye tbe e n e s tabl is h e d. Th is pape r is inte nde d to corre cts om e ofth e s e m is conce ptions . Th e re is a te nde ncy to as s um e th atbe ing be l ow DRL m e ans ade q uate optim iz ation, DRLs provide good tool s in pre vious ye ars w h e n th e s pre ad of dos e s w e re by far l arge orde r of m agnitude and th e s h ape ofth e dos e dis tribution curve w as righ t-s k e w e d as ym m e tric.13 H ow e ve r, th e tre nd h as ch ange d ove r tim e w ith im prove m e nts in te ch nol ogy and practice . In th e w ords ofProfe s s or M e dan Re h ani ofth e gl obaloutre ach for radiation prote ction, “Th e re is no probl em

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w ith DRLs but s topping at DRLs and us ing DRLs in w ays it w as not s uppos e d to be us e d cre ate s probl e m s ”. Th e re are a num be r ofprobl e m s w ith th e w ay DRLs are us e d as outl ine d in a re ce ntcom m e ntary.13 Th e re h as be e n a te nde ncy to us e diagnos tic re fe re nce l e ve l s as de facto dos e l im its th at s h oul d not be e xce e de d w h ich be com e s de trim e ntalto patie nts ofh igh e r body buil d w h o actual l y ne e d dos e s h igh e r th an th e DRLto ge tade q uate im age q ual ity. De s pite ne arl y 30 ye ars of its e xis te nce DRLs for adul t patie nts h ave be e n confine d to re pre s e ntative s tandard s iz e patie nts w h e re as m os t patie nts e ncounte re d in dail y practice are nots tandard s iz e d DRLs w e re de ve l ope d for a de fine d te ch nol ogy and it w as e nvis age d th at th e y w oul d be update d w ith te ch nol ogy ch ange s . Th is h as notbe e n done in m os t countrie s w ith s om e fe w e xce ptions . Oth e r are as al so incl ude ; Us e ofDRLs for individualpatie nts Us e ofe ffe ctive dos e for DRL CURRENT TRENDS IN DIAGNOSTIC REFERENCE LEVELS Ove r th e pas tfe w de cade s th e re h ave be e n grow ing conce rns about radiation prote ction in m e dicine w orl dw ide w ith particul ar e m ph as is on radiation prote ction of patie nts .14 Th is is due to incre as e in te ch nol ogicaladvance s as w e l las incre as ing popul ation e xpos ure l e ading to grow ing conce rns about th e ne e d for ade q uate radiation prote ction. Th e re fore , m uch e m ph as is is l aid on th e ne e d to e s tabl is h diagnos tic re fe re nce l e ve land to update e xis ting one s cons is te nt w ith curre nt practice and te ch nol ogy.3,15 To th at e ffe ct s om e tim e l as tye ar in 2016 th e ICRP h as re vie w e d its docum e nton DRLs .16 Th e docum e nt w as in th e publ ic dom ain for a pe riod ofth re e m onth s for cons ul tations . Th e pe riod for cons ul tation is ove r and th e com m itte e h as s ubm itte d th e ir finaldraft to th e m ain com m is s ion aw aiting publ ication.16 Som e us e fule xce rpts e xtracte d from a pre s e ntation by th e im m e diate pas tch air ofth e ICRP Com m itte e 3 atth e re ce ntl y concl ude d Europe an Congre s s for Radiol ogy (ECR 2017) are pre s e nte d be l ow for th e be ne fit of th e radiol ogy com m unity e s pe cial l y th os e ofus from th e de ve l oping countrie s .


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Re com m e ndations or Main points from th e ICRP’s DRL docum e nt ue is cons ide re d to be e xce e de d w h e n 1) A DRLval th e l ocalm e dian val ue of th e appropriate DRL q uantity for a re pre s e ntative s am pl e of patie nts w ith in an agre e d w e igh trange is gre ate r th an th e l ocal , nationalor re gionalDRLval ue . H e re cons is te ntl y m e ans ‘in a m ajority ofcas e s ’ and not‘ove r a pe riod oftim e ’ 2) DRLval ue s h al lnotbe us e d for individualpatie nts or as a trigge r l e ve lfor individualpatie nts or individuale xam inations 3) Al lindividual s w h o h ave a rol e in s ubje cting patie nts to a m e dicalim aging proce dure s h oul d be fam il iar w ith DRLs as a toolfor optim iz ation ofprote ction (s h oul d be introduce d for training program s for radiation prote ction) 4) Com paris on of l ocalpractice s to DRL val ue s is nots ufficie nt, by its e l f, for optim iz ation ofprote ction. Action is re q uire d to ide ntify and addre s s any de ficie ncie s . Th e h igh e s tpriority for any diagnos tic im aging e xam ination is ach ie ving im age q ual ity (diagnos tic inform ation) s ufficie nt for th e cl inical purpos e . 5) Th e conce pt and prope r us e of DRLs s h oul d be incl ude d in th e e ducation and training program m e s of th e h e al th profe s s ional s invol ve d in m e dical im aging w ith ionis ing radiation (al s o as part of patie ntinfo) 6) Quantitie s us e d for DRLs s h oul d as s e s s th e am ountofionis ing radiation appl ie d to pe rform a particul ar m e dicalim aging tas k , and s h oul d be e as il y m e as ure d or de te rm ine d. DRL q uantitie s as s e s s th e am ount ofionis ing radiation us e d for a m e dicale xpos ure notabs orbe d dos e to a patie nt or organ. 7) Com pl iance w ith DRLs doe s notindicate th atth e proce dure is pe rform e d atan optim iz e d l e ve lw ith re gard to th e am ount of radiation us e d. Th e Com m i s s ion re co gni z e s th at ad di ti on al im prove m e ntcan be obtaine d by us ing th e m e dian val ue (50th pe rce ntil e of th e dis tribution us e d to s e tth e nationalDRLval ue ) 8) Th e com m is s ion re com m e nds s e tting l ocaland nationalDRLval ue s bas e d on s urve ys ofth e DRL q uantitie s for proce dure s pe rform e d on appropriate s am pl e of patie nts . Th e us e of ph antom s is not s ufficie ntin m os tcas e s .

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9 ) Cal ibration ofal ldos im e te rs s h oul d be pe rform e d re gul arl y and s h oul d be trace abl e to a prim ary or s e condary s tandard l aboratory. 10) Th e accuracy of DRLq uantity data produce d by and trans fe rre d from x-ray s ys te m s s h oul d be pe riodical l y ve rifie d by a m e dicalph ys icis t. 11) DRLval ue s are de pe nde nton th e s tate ofpractice and avail abl e te ch nol ogy (incl uding pos t-proce s s ing s oftw are ) ata particul ar pointin tim e . 12) For inte rve ntionalproce dure s , com pl e xity of th e proce dure m ay be cons ide re d in s e tting DRLs and a m ul tipl ying factor for th e DRLval ue m aybe appropriate for m ore com pl e x cas e s ofa proce dure . 13) Nationaland re gionalDRLval ue s s h oul d be rais e d atre gul ar inte rval s (3-5 ye ars ) or m ore fre q ue ntl y w h e n s ubs tantialch ange s in te ch nol ogy, ne w im aging protocol s or pos t-proce s s ing of im age be com e avail abl e. 14) Ifa l ocalor nationalDRLval ue for any proce dure is e xce e de d, an inve s tigation s h oul d be carrie d outw ith outundue de l ay, and appropriate corre ctive actions s h oul d be tak e n. 15) Corre ctive action?(O ptim iz ation of prote ction) s h oul d incl ude a re vie w ofe q uipm e ntofe q uipm e nt pe rform ance , th e s e ttings u s e d, and th e e xam ination protocol s . Th e factors m os t l ik e l y to be invol ve d are s urve y m e th odol ogy, e q uipm e nt pe rform ance , proce dure protocol , ope rator s k il l and, for inte rve ntionalte ch niq ue s , proce dure com pl e xity.

Re fe re nce s 1. M uh ogora W E, Ah m e d NA, Al m os abih i A e t al , Patie ntdos e s in radiograph ic e xam inations in 12 countrie s in As ia, Africa Eas te rn Europe : initial re s ul ts from IAEA proje cts . AJR. 2008; 19 0: 1453-61 2. Ciraj-bje l ac O, Be ganovic A, FajD, e tal . Radiation prote ction ofpatie nts in diagnos tic radiol ogy: Status of practice in five Eas te rn-Europe an countrie s , bas e d on IAEA proje ct. Eur J Radiol . 2011;1-4. 3. E urope an Com m is s ion. Diagnos tic Re fe re nce Le ve l s in Th irty-s ix Europe an Countrie s . Radiation


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Prote ction No. 180 Part2/2 Publ ications office of th e Europe an Union. Luxe m bourg. 2014 4. Vas s il e va J, Re h ani M . Diagnos tic Re fe re nce Le ve l s AJR. 2015;204: W 1-W 3 5. Inte rnationalAtom ic Ene rgy Age ncy. Radiation prote ction and s afe ty of radiation s ource s : inte rnationalbas ic s afe ty s tandards . Ge ne rals afe ty re q uire m e nts Part3. IAEA Safe ty Standards Se rie s , Vie nna. 2014 6. Inte rnationalAtom ic Ene rgy Age ncy Diagnos tic Re fe re nce Le ve l s in M e dicalIm aging h ttp://rpop. iae a.org 7. Inte rnational Com m is s ion on R adiol ogical Prote ction. ICRP Publ ication 121. Radiol ogical prote ction in pae d iatric di agnos tic and inte rve ntionalradiol ogy. Annal s ofth e ICRP. 2013; 42;2: 1-63.

dos e (AQD). Br J Radiol2015;88: 20140344. 14. Inte rnationalAtom ic Ene rgy Age ncy. Radiation prote ction in m e dicine : Se tting th e s ce ne for th e ne xt de cade . Proce e dings of an Inte rnational Confe re nce organis e d by th e Inte rnationalAtom ic Ene rgy Age ncy, h os te d by th e Gove rnm e nt of Ge rm any Co- s pons ore d by th e W orl d H e al th O rganis ation and h e l d in Bonn, Ge rm any 3- 7 De ce m be r 2012 (IAEA) Vie nna 2015 15. Europe an Com m is s ion. Europe an Guide l ine s on DRLs for pae diatric im aging. Europe an Union. Luxe m bourg. 2015 16. Vano E. ICRP pe rs pe ctive : from m e th odol ogical re l ate d DRLto DRLbas e d on cl inicalindications . Pos tgraduate e ducationalprogram m e Euros afe im aging s e s s ion. ECR onl ine . Avail abl e at;e cronl ine .m ye s r.org/e cr2017/?

8. Inte rnationalCom m is s ion on Radiol ogicalProte ction. Radiol ogicalprote ction and s afe ty in m e dicine : ICRP publ ication 73. Ann ICRP, 19 9 6; 26: 23-4. 9 . Inte rnationalCom m is s ion on Radiol ogicalProte ction. Diagnos tic re fe re nce l e ve l s in m e dicalim aging: re vie w and additionaladvice . Annal s ofth e ICRP, 2001;31(3): 33-52. 10. Inte rnationalCom m is s ion on Radiol ogicalProte ction. Radiol ogicalProte ction in M e dicine . ICRP Publ ication 105. Ann. ICRP. 2007;37(6): El s e vie r. 11. NationalCouncilon Radiation Prote ction and M e as ure m e nt. Re fe re nce l e ve l s and ach ie vabl e dos e s for m e dicaland de ntalim aging: re com m e ndations for th e Unite d State s . Be th e s da M D; NCRP Re port. 2012;172. 12. Inte rnationalAtom ic Ene rgy Age ncy. Dos im e try in Diagnos tic Radiol ogy for Pae diatric Patie nts . IAEA H um an H e al th Se rie s No. 24 Vie nna. 2013 13. Re h ani, M M .Lim itations of diagnos tic re fe re nce l e ve l(DRL) and introduction ofacce ptabl e q ual ity

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