radiation dose from exposure to computed tomo - Pakistan Journal of

ORIGINAL ARTICLE

RADIATION DOSE FROM EXPOSURE TO COMPUTED TOMOGRAPHY SCAN OF THE BRAIN IN A REFERENCE HOSPITAL IN NIGERIA Nzotta C.C,1 Egbe N.,2 Adejoh T,3 Nkubli B. F,4 Ezeador I.S1 De partm e ntofRadiograph y and Radiol ogicalScie nce s , Col l e ge ofH e al th Scie nce s , Nnam diAz ik iw e Unive rs ity, Nne w i Cam pus , Nige ria. 2 M e dical Radiograph y De partm e nt, Col l e ge ofH e al th Scie nce s , Unive rs ity ofCal abar, Nige ria. 3 De partm e ntofRadiol ogy, Nnam diAz ik iw e Unive rs ity Te ach ing H os pital , Nne w i, Nige ria. 4 De partm e ntofM e dicalRadiograph y, Col l e ge ofM e dicalScie nce s , Unive rs ity ofMaiduguri, M aiduguri, Nige ria. 1

PJR April - June 2016; 26(2): 77-80

ABSTRACT BACKGROUND: Diagnos tic re fe re nce l e ve l s h ave be e n s e tby re l e vantre gul atory age ncie s in diffe re ntcountrie s as a re s ul t of th e biol ogicalris k s from e xpos ure to ioniz ing radiation. H ow e ve r, no s tudy h as be e n carrie d out in our ce ntre to ge ne rate data th at m ay com e in h andy in e s tabl is h ing a l ocalre fe re nce l e ve l . OBJECTIVE: To q uantify th e abs orbe d dos e from Com pute d Tom ograph y (CT) s can of th e brain us ing th e CT dos e ch art and th e rm ol um ine s ce ntdos im e te rs (TLD) w ith a vie w to e s tabl is h ing l ocaldiagnos tic re fe re nce l e ve l s (DRL) for our ce ntre . METHODS: A pros pe ctive , cros s -s e ctionals tudy invol ving 30 patie nts age d 4 m onth s to 72 ye ars re fe rre d for brain CT. Patie nts w e re pos itione d according to s tandard protocol s for brain CT. Tw o TLD ch ips w e re pl ace d on th e gl abe l l a and occiput re s pe ctive l y. Th e pos te rior one w as h e l d in pl ace by th e w e igh t of th e h e ad w h il e th e ante rior one w as h e l d in pl ace w ith tape . W ith an az im uth of180°, th e pos te rior TLD w as m ark e d as ‘e ntrance ’ and th e ante rior as ‘e xit.’ Th e TLDs w e re onl y de tach e d at th e e nd of th e inve s tigation. Th e y w e re s e al ed s e parate l y in s m al ltrans pare ntce l l oph ane s bags and s e ntfor re ading ata re gionalradiation dos im e tric l aboratory. Sim pl e s tatis ticaltool s w e re us e d to de te rm ine ce ntralte nde ncie s . RESUL TS: Th e abs orbe d radiation dos e note d in our ce ntre h ad a range of38.6 - 66.4 m Gy (1.9 3-3.32 m Sv) from CT dos e ch artand 0.6-104 m Gy (0.035.20 m Sv) for TLD re s pe ctive l y. Th e m e an col l e ctive dos e for CT (50.3 ± 10.2 m Gy;2.52 ± 0.51 m Sv) w as s l igh tl y h igh e r th an for TLD (40.83 ± 26.4 m Gy;2.04 ± 1.32 m Sv). A paire d-s am pl e t-te s t at a probabil ity l e ve lof p < 0.05 (for s ignificance ) yie l de d a p-val ue of0.05 indicating th atth e re is a s tatis ticals ignificantdiffe re nce be tw e e n both m e ans . CONCLUSION: Th e dos e from our practice is w ith in th e range got from oth e r s tudie s . H ow e ve r, furth e r dos e re duction is pos s ibl e w ith a m ore care fulte ch niq ue . Keywords: Radiation, dos e , Com pute d Tom ograph y, TLD

Introduction Th e tre nd ofincre as ing popul ation e xpos ure to m e dical diagnos tic s ource s of radiation, attribute d to th e grow ing us e of com pute d tom ograph y s cans h as rais e d conce rns aboute xpos ure to radios e ns itive Correspondence : Dr. Nk ubl i B. F De partm e ntofM e dicalRadiograph y, Col l e ge ofM e dicalScie nce s , Unive rs ity of Maiduguri, M aiduguri, Nige ria. Ph one : + 234 (0) 8063624220 Em ail : active fl avour@ yah oo.com

organs .1 In m e dicalim aging, CT is th e m os tim portant th ough th e radicontributor to patie nte xpos ure s .2 Al ation e xpos ure from com pute d tom ograph y s cans is s ubs tantial l y l ow e r th an th at from radioth e rapy, m ul tipl e com pute d tom ograph y s cans coul d re s ul tin non-trivialcum ul ative dos e s to radios e ns itive organs l ik e th e th yroid and e ye s . 1

Subm itte d 21 Se pte m be r 2015, Acce pte d 2 Nove m be r 2015

PA K I S TA N J O U R N AL O F R A D I O L O GY

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Th e be ne fits de rive d from a prope rl y conducte d CT proce dure w il lcontinue to outw e igh th e s m al lris k s as s ociate d w ith it, none th e l e s s , itis im portantto be abl e to s pe cifical l y q uantify th e ris k s . 3 H ow e ve r, as s e s s ing th e m agnitude of e xpos ure or pote ntial ris k s from diagnos tic proce dure s is a tas k m os t ph ys icians find difficul t to do.4 Effe ctive dos e , w h ich is a ris k -w e igh te d m e as ure of radiation to organs in th e body as s ociate d w ith radiol ogicale xam ination, is cons ide re d a good indicator ofradiol ogicalris k . W h il e m e th ods to cal cul ate e ffe ctive dos e h ave be e n e s tabl is h e d th e y de pe nd h e avil y on th e abil ity to e s tim ate th e dos e to radios e ns itive organs from th e radiol ogicalproce dure s . Th e de te rm ination of th e radiation dos e to th e s e organs is ve ry difficul t, and dire ctm e as ure m e ntis notpos s ibl e. Th e re fore organ dos e s are e s tim ate d from m e as urabl e q uantitie s s uch as norm al iz e d organ dos e data e xpre s s e d as abs orbe d dos e .3 Th e Inte rnationalCom m is s ion on Radiol ogicalProte ction advice s th at Diagnos tic Re fe re nce Le ve l s (DRLs ) be e s tabl is h e d. Th e s e DRLs are us e d in m e dicalim aging w ith ioniz ing radiation to indicate w h e th e r, in routine conditions , th e patie nt dos e or adm inis te re d activity (am ountofradioactive m ate rial ) from a s pe cifie d proce dure is unus ual l y h igh or l ow for th atproce dure . Th e pre s e ntInte rnationalCom m is s ion on Radiol ogicalProte ction (ICRP) advice doe s nots pe cify q uantitie s , num e ricalval ue s or de tail s of im pl e m e ntation for DRLs . ICRP cons ide rs th at any re as onabl e and practicalapproach , cons is te ntw ith th e advice , w il lim prove th e m anage m e ntof patie nt dos e s in m e dicalim aging.5 Th e re h as re ce ntl y be e n s om e e m ph as is on conducting m ore l ocal iz e d s tudie s of patie nt dos e and as s ociate d ris k e s tim ate from radiol ogicale xam inations tak ing into accountth e s pe cific m ach ine s and de partm e ntalprotocol s th atcoul dh el p in e s tabl is h ing re fe re nce l e ve l s for m onitoring dos e from s uch radiol ogicale xam inations . Al th ough , w ork s by re s e arch e rs from oth e r ce ntre s ce rtainl y provide s an e xce l l e nt re s ource for e val uating dos e s from radiol ogical e xam inations , a l ocals tudy coul d provide m ore re l evant inform ation. Th is w il lh e l p to e s tabl is h s om e re fe re nce and guidance dos e val ue s and w oul d al l ow us to m onitor any ch ange s ove r tim e th atm igh taris e from aging e q uipm e ntor ch anging protocol s . It coul d al s o give us a m e ans to com pare dos e s w ith th atof

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oth e r h os pital s and re gions . 3 S e ve ralEurope an countrie s h ave e s tabl is h e d DRLs 6 but th is is not th e cas e in our e nvironm e nt. O ur w ork is aim e d at ge ne rating data th at m ay be us e fulin e s tabl is h ing l ocalDRL.

Materials and Methods A pros pe ctive , cros s -s e ctionals tudy invol ving 30 patie nts age d 4 m onth s to 72 ye ars re fe rre d for brain CT be tw e e n June 23 to Jul y 7, 2014. A 32sl ice Tos h iba CT s canne r th at be cam e ope rational in 2013 w as avail abl e at th e ce ntre . Code d TLD ch ips (TLD LiF-100) w e re cal ibrate d us ing H ars h aw 4500 dualTLD re ade r and s uppl ie d by a re gional Ce ntre for Ene rgy Re s e arch and Training. Patie nts w e re pos itione d according to s tandard protocol s for brain CT. A TLD dis k w as pl ace d on th e gl abe l l a and anoth e r on th e occiput re s pe ctive l y and h e l d in pl ace w ith tape . Th e y w e re onl y de tach e d w h e n th e e xam ination for e ach patie ntw as te rm inate d. Expos ure factors w e re 150 k Vp and 150 m As for >10 ye ars and 150 k Vp and 135 m As for  10 ye ars . An az im uth of180° w as s e l e cte d to e ns ure pe ne tration th rough th e occiput and to m inim iz e e ye dos e . Th e pos te rior and ante rior TLDs w e re s ubs e q ue ntl y tagge d as ‘e ntrance ’ and ‘e xit’ re s pe ctive l y. W h e n de tach e d th e TLDs w e re care ful l y s e al e d in tiny trans pare nt ce l l oph ane bags and s e ntfor re ading atth e s tandard radiation dos im e tric l aboratory ofth e re gionalCe ntre for Ene rgy Re s e arch and Training th ats uppl ie d th e m . De s criptive s tatis ticaltool s w e re us e d to de te rm ine ce ntralte nde ncie s . A tis s ue w e igh ting factor of 0.05 (as re com m e nde d by th e ICRP) for brain w as us e d to conve rt th e abs orbe d dos e (in m Gy) to e ffe ctive dos e (in Sie ve rt).

Results A totalof 30 patie nts participate d in th e s tudy w ith 30% (n=9 ) h aving an additionalcontras tinve s tigation and 70% (n=21) h aving no contras t adm inis tration. Th e age of th e patie nts and abs orbe d dos e as e s tabl is h e d by both th e CT dos e ch art and TLD is


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s um m ariz e d in (Tab. 1). A com paris on ofs om e s tudie s on abs orbe d dos e done by oth e r re s e arch e rs is give n in (Tab. 2). Age (Years)

S.No

Absorbed dose Absorbed dose Contrast CT (mSv) TLD (mSv)

1. 25 2.49 2. 13 2.54 3. 3 3.31 4. 30 3.31 5. 71 3.30 6. 72 2.50 7. 50 2.14 8. 25 3.31 9. 45 3.31 10. 38 2.9 6 11. 45 2.9 1 12. 47 2.17 13. 46 2.21 14. 0.33 2.21 15. 0.9 2 1.9 3 16. 9 1.9 3 17. 1 2.16 18. 22 2.1 19 . 55 2.1 20. 70 2.9 0 21. 55 2.16 22. 58 3.14 23. 67 2.22 24. 65 2.22 25. 67 1.9 3 26. 28 1.9 3 27. 55 2.16 28. 33 2.54 29 . 12 3.32 30. 62 2.09 Mean 29.00 ± 23.6 2.5157 ± 0.51

2.9 04 2.207 5.09 9 1.512 2.419 2.9 0.6631 1.6 2.3 0.055 0.784 2.9 27 3.415 1.334 1.142 2.9 69 0.182 0.028 2.455 1.14 2 2.8 3.401 1.3 1.1 2.9 2 2.3 5.2 0.2 2.0412 ± 1.32

Contras t Contras t Contras t Contras t Contras t Contras t Contras t Contras t Contras t

Table 1: Effe ctive dos e ch aracte ris tics ofth e patie nts

Authors

Location

Pre s e nts tudy Nige ria O riggi e Os e i e

7 tal

3 tal

Dose (mSv)

Sample kVp mAs size maximum maximum

2.5

30

150

150

Ital y

1.8

56

140

580

Canada

1.8

94

138

100

9 O gbol e e tal

Nige ria

2.8

50

120

215

8 Brix e tal

Ge rm any

2.8

9 ,000

122

317

Table 2: Com paris on ofabs orbe d dos e s

Discussion Th e re s ul tofour s tudy e s tabl is h e d a m e an e ffe ctive dos e of 50.3 ± 10.2 m Gy;2.52 ± 0.51 m Sv for our popul ation us ing com pute d tom ograph y dos e ch art and 40.83 ± 26.4 m Gy;2.04 ± 1.32 m Sv w h e n m e a-


s ure d by TLDs . Itw as note d th atgl obal l y th e m e an e ffe ctive dos e for brain CT range d be tw e e n 1.8 to 2.8 m Sv (Tab. 2). Th e m axim um val ue got from our s tudy as indicate d by CT dos e ch art w as 2.5 m Sv, an indication th at abs orbe d dos e in th e cours e of our practice at our ce ntre fal l s w ith in acce ptabl e l im it. As e xpe cte d, CT dos e ch artgave a h igh e r val ue th an TLD al th ough th e range w as q uite narrow . A paire d- s am pl e t- te s t yie l de d a t- val ue of 2.044 indicating th at th e re is no s tatis tical l y s ignificant diffe re nce be tw e e n both m e ans . Al s o, it s h oul d be note d th atval ue s re porte d by CT dos e ch art do not tak e into accou nt patie nt s iz e or dos e -re duction te ch niq ue s s uch as autom atic e xpos ure control incorporate d into th e s ys te m and im pl e m e nte d during th e s tudy. Our CT s canne r is a 32-s l ice m ach ine . As a cons cious dos e -re duction te ch niq ue w e do not e xce e d 150 m As for adul ts . Ge tting 2.5 m Svas th e m e an e ffe ctive dos e give s h ope th at w ith a furth e r re duction in e xpos ure param e te rs w ith out com prom is ing re s ol ution, a furth e r re duction in dos e is pos s ibl e . In a s urve y carrie d out in Ge rm any to inve s tigate dos e from s ingl e sl ice and m ul ti-s l ice CT s canne rs th e auth ors note d th atbrain CT accounte d for th e m os t fre q ue nt inve s tigation (27.1% ). Th e y s ubs e q ue ntl y e s tabl is h e d a m e an col l e ctive e ffe ctive dos e of 2.8 m Sv (Tab. 2) for th e ir popul ation and concl ude d th at cons ide rabl e dos e re duction w as obs e rve d w h e n s ingl e -s l ice CT w as us e d to e xam ine patie nts .8 Th e re duction in our dos e rate com pare d to th e irs m ay not be unconne cte d w ith th e m uch l ow e r m As of 150 w e us e d as agains tth e 317 m As us e d by th e m . It is appare nt th at as ide us ing s ingl e -s l ice CT, a re duction in e xpos ure param e te rs l ik e m As m ay pos s ibl y re duce dos e . A s im il ar w ork done in our l ocal ity to de te rm ine th e dos e ofCT e xam inations and provide a te m pl ate for dos e optim iz ation concl ude d th at CT dos e s in th e ir ce ntre w e re h igh . Th e y e s tabl is h e d an e ffe ctive dos e 9 ite rature cons ul te d of2.8 m Sv, th e h igh e s ts e e n in l by us (Tab. 2). Th e ir s am pl e s iz e w as 50 CT brain patie nts and th e m axim um m As w as 215. Th e ir m ach ine w as al s o m ul ti-de te ctor l ik e ours . Th e ir finding pos s ibl y val idate s our th ink ing th atin th is l ocal ity th e re is a ne e d to pay cons cious atte ntion to dos e re duction te ch niq ue s . Exam pl e s from oth e r cl im e s s h ow s s om e re duction in dos e l e ve l s irre s pe ctive


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ofth e type of CT m ach ine us e d. In a cl os e l y-s im il ar w ork carrie d outin Ne th e rl ands us ing m ul ti-de te ctor CT w h ich invol ve d 186 patie nts , a m e an e ffe ctive dos e of 1.5 m Sv w as e s tabl is h e d 2 for brain CT. Al th ough th e m As val ue s for th e inve s tigations w e re not give n, it w as l ik e l y th at th e m As w as cons ide rabl y re duce d to h ave arrive d at s uch l ow l e ve lof e ffe ctive dos e . Anoth e r w ork us e d a m axim um m As of 100 on 9 4 patie nts and de rive d a m e an e ffe ctive dos e of 1.8 m Sv and 1.1 m Sv for for adul tand pe diatric h e ad CT e xam inations re s pe ctive l y. 3 In our w ork h ow e ve r, w e got m uch h igh e r val ue s for pe diatrics (Tab. 1) probabl y be caus e of th e 135 m As w e us e d w h ich is cons ide rabl y h igh e r 3 th an th at re porte d by O s e i. An e ffe ctive dos e of 1.8 m Sv w as got from s ingl e -s l ice CT us e d on 56 patie nts in Ital y. A s urpris ingl y h igh m As of580 w as us e d ye t th e ir val ue w as l ow e r th an th at got from our s tudy. Th is buttre s s e s th e argum e nt of Brix e t idate s our th ink ing in th atre gard. al ,8 and cons ol

Conclusion A m e an e ffe ctive dos e of2.5 m Svfor brain w as note d in our ce ntre . Al th ough th is did notdiffe r s ignificantl y from val ue s got from oth e r w ork s furth e r dos e re duction is pos s ibl e w ith care fuland cons cious dos e -re duction practice s . W e al s o note d th at dos e val ue s ge ne rate d by TLDs w e re l ow e r th an th atgot from CT dos e ch artand th e diffe re nce is s tatis tical l y s ignificant. M any ofour vol unte e rs w e re ne ith e r am bul ant nor coul d s tand e re ct. Th is w as a l im itation as w e igh t as s e s s m e ntcoul d notbe m ade . Th e TLD ch ips coul d al s o not be adjus te d on th e patie nts to corre s pond w ith e ach s l ice th ick ne s s s e l e cte d and h e nce re ce ive optim um irradiation. Th is m os tl ik e l y contribute d to th e l ow e r val ue s got. Th e auth ors al so ack now l e dge th e factth atour s am pl e s iz e w as s m al l com pare d to oth e r s tudie s , th is is due to l ow patie nt th rough put to th e ce ntre . Th is doe s not h ow e ve r ne gate th e findings ofth is s tudy. W e re com m e nd furth e r as s e s s m e ntofpatie nts us ing furth e r re duction in e xpos ure param e te rs to track ch ange s in dos e l e ve l s , if any.


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