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SYSTEMATIC REVIEW

Dose optimization by altering the operating potential and tube

current exposure time product in dental cone beam CT:

a systematic review

1Rebekah Goulston, 2Jonathan Davies, 2Keith Horner and 3Frederick Murphy

1Dental Radiology Department, University Dental Hospital of Manchester, Manchester, UK; 2University of Manchester, School of Dentistry, Manchester, UK; 3School of Health Sciences, University of Salford, Salford, UK

Objectives: Current guidelines highlight the need to optimize exposure parameters on CBCTequipment to levels that are as low as diagnostically acceptable. This systematic review aimed

to answer the question “Can altering operating potential (kV) and tube current exposure timeproduct (mAs) on CBCT machines reduce radiation dose to patients undergoing dental and/ or maxillofacial scans without a detrimental impact on image quality/diagnostic accuracy?”Methods: Studies were selected and results reported following the Preferred Reporting Itemsfor Systematic Reviews and Meta-Analyses (PRISMA) method. For each individual study, twoauthors (RG and JD or KH) independently extracted data using a specifically designed collectionform, and an overall quality value was assigned using the Grading of RecommendationsAssessment, Development and Evaluation (GRADE) system. Any disagreements in the overallquality value of a study were resolved by discussion between the current authors.Results: Nearly 75% of studies were considered to be of low or very low methodologicalquality using the GRADE system, and more studies stated that their results applied only inthe specific situations they had investigated. However, most studies demonstrated that patientdose reduction is possible without a clinically relevant reduction in image quality.

Conclusions: For many CBCT machines, it should be possible to optimize one, or more, of theinvestigated exposure parameters and therefore reduce patient radiation dose, while maintainingdiagnostic image quality for some diagnostic tasks. However, more rigorous research is still required.Dentomaxillofacial Radiology (2016) 45, 20150254. doi: 10.1259/dmfr.20150254

Cite this article as: Goulston R, Davies J, Horner K, Murphy F. Dose optimization by alteringthe operating potential and tube current exposure time product in dental cone beam CT:a systematic review. Dentomaxillofac Radiol 2016; 45: 20150254.

Keywords: cone-beam computed tomography; exposure parameters; image quality; radiationprotection; review, systematic

Introduction

Dose optimization is a fundamental principle of radia-tion protection of individuals as part of healthcare. Thishas been defined as keeping doses “as low as reasonablyachievable (ALARA principle), economic and societalfactors being taken into account” and involves both thedesign and construction of equipment and day-to-dayworking procedures.1

Dental CBCT is still a relatively new imaging tech-nology, but the volume of research related to this im-

aging technology has grown steadily over the past

decade.2,3 Guideline documents, recently reviewed by

Horner et al(2015),4 have been devised at local, national

and supranational levels to assist dentists, radiologists,

radiographers/technologists and medical physicists in

safe use of CBCT; some of these give general guidance

on optimization, although detail is absent. For example,

the European guidelines5 state, “X-ray tube voltage andCorrespondence to: Rebekah Goulston. E-mail: [email protected]

Received 4 August 2015; revised 23 November 2015; accepted 5 January 2016

Dentomaxillofacial Radiology (2016) 45, 20150254ª 2016 The Authors. Published by the British Institute of Radiology

birpublications.org/dmfr

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tube current-exposure time product should be adjust-able on CBCT equipment and must be optimised duringuse according to the clinical purpose of the examina-tion…”; however, there is no specific instruction on howoptimization is to be achieved in practice. Similar gen-eral guidance is seen in other publications, for example

in the USA6,7 and UK.8Radiation dose and image quality are inextricably

linked and, as highlighted in the Image Gently® inDentistry campaign (http://www.imagegently.org/ ),a better description of optimization efforts should be toreduce exposures to levels as low as diagnostically ac-ceptable (ALADA principle).9 The question underlyingthis review was: “Can altering operating potential[kilovoltage (kV)] and tube current exposure timeproduct [milliampere second (mAs)] on CBCT machinesreduce radiation dose to patients undergoing dentaland/or maxillofacial scans without a detrimental impacton image quality and therefore diagnostic accuracy?”

The aim was thus to answer this question by performinga systematic review of the currently available evidence.

Methods and materials

Eligibility criteriaPrior to any literature search being performed, the in-clusion and exclusion criteria for the review were de-termined. A study would be considered for inclusion inthe review if it investigated the impact that differentdental CBCT machine exposure parameters had onimage quality or diagnostic accuracy/outcome. Expo-sure parameters were defined as kV, milliampere (mA)or time (altered via different voxel settings and/or tubeand detector rotation). In addition, CBCT vs multisliceCT dose and image quality studies would be includedonly if different image/data sets were produced usingmore than a single set of exposure parameters on thesame CBCT machine because, currently, this is the onlyway that a comparison of image quality can be madebetween different CBCT exposure parameters. Thefollowing types of study would be excluded:

(1) Dose studies that did not consider image qualityand/or diagnostic accuracy when altering exposureparameters.

(2) Data relating to different fields of view, as they werenot included in the definition of an exposureparameter; articles which discuss field of view maybe included if kV, mA or time have also beenaltered/considered.

(3) Review/discussion articles that were not systematicreviews of the literature.

(4) Non-English literature without an English abstract.Publications with abstracts only in English would stillbe read, considered and discussed. If the abstractappeared to report a study which satisfied the in-clusion criteria, a pragmatic decision would be takenabout the feasibility of translation.

Information sourcesTwo electronic databases were searched: PubMed/ MEDLINE (1998 – 25 May 2015) and Ovid/EMBASE(1998 – 25 May 2015). All databases were searched frommid-1990s, as the f irst publication on dental CBCT wasin the late 1990s.10,11 These articles were then put

through the first stage of study selection. In addition,the primary author manually searched through thereference lists of all the articles eligible for inclusion inthe study to find any further studies that many be eli-gible but had been missed during the database searches.The other authors were also consulted to assess whetherany important citations were missing.

SearchSearch terms used for Ovid/EMBASE and PubMed/ MEDLINE can be seen in Figure 1.

Study selectionSelection for inclusion was in two stages. During thefirst “screening” stage, the primary author (RG) readthe journal titles and full abstracts of the studies found,to see if they fitted the eligibility criteria; those that metthe criteria went through to stage two, where the pri-mary author read the full-text article to ensure thestudies continued to meet the pre-defined eligibilitycriteria. Where the primary author was uncertain aboutthe eligibility of a study, this was resolved by discussion

Figure 1 Ovid/EMBASE and PubMed/MEDLINE searches.

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with the other authors. This occurred on three occa-sions, and on all three occasions, it was decided that thestudy being considered did not meet the eligibility cri-teria; so, these studies were excluded from the review.

Data collection process and data items

The unique nature of most of the studies reviewedmeant that well-established extraction tools, such asthose produced by the Critical Appraisal Skills Pro-gramme (Oxford, UK),12 were not appropriate to an-swer the question being asked by this review. Asa result, having considered the objectives of the presentstudy and the methodologies used by other systematicliterature reviews investigating aspects of dentalradiology,5,13,14 the primary author developed an ex-traction form specifically for this systematic review(Figure 2). To ensure the extraction tool resulted in theimportant information being collected, the process wasreviewed in relation to the study objectives after the first

five studies had been appraised. At this point, it wasnoted that some important data had been excluded, and

as a result, an additional field was added to the form inwhich the CBCT machine(s) used was recorded.

Two of the authors reviewed every eligible publica-tion. The primary author, who has no conflict of in-terest to declare, reviewed all the studies. The secondand third authors (JD and KH, respectively) each

reviewed approximately 50% of the studies. However,the second author had been an author on two of thestudies reviewed, while the third author had been anauthor on one study eligible for review and had super-vised the work of another. As the second and thirdauthors had not co-authored any of the literature beingreviewed, where these authors had involvement ina particular study, then the alternate author wasassigned to review it, thus avoiding any potential con-flict of interest and reducing bias. All studies where noauthor had a conflict of interest were randomly allo-cated between these two authors. Any disagreements inthe overall quality value of a study following this data

extraction were resolved by discussion between thesethree authors.

Figure 2 Extraction form specifically designed for this systematic review.

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Risk of bias in individual studiesThe overall quality of each study was assessed accord-ing to the Grading of Recommendations Assessment,Development and Evaluation (GRADE) system de-scribed by Guyatt et al.15 This system was chosen as thebest method to assess the quality of the studies reviewed

because, unlike other quality-rating tools such asSIGN50,16 GRADE takes into account major factorsthat have an impact on clinical use, not just the type of study and its outcome.15 The Scottish IntercollegiateGuidelines Network has replaced SIGN50 with anadapted version of GRADE for its own recom-mendations.16 The GRADE system was also success-fully used by Petersson et al14 in their systematic reviewof radiological diagnosis of periapical bone tissuelesions in endodontics.

Risk of bias across studiesThe strategies of cross-referencing with systematic

reviews included in the present study and discussionbetween all three authors about studies for inclusionwere designed to decrease the probability of any wholestudies being missed. To reduce the risk of data fromindividual studies being excluded, before commencingthe study-selection process, it was suggested that if dataappeared to be missing, authors of the individual studiesshould be contacted for clarification. This strategy was,however, not necessary.

Additional analyses and synthesis of resultsThe question of the feasibility of performing quantita-tive statistical analysis/meta-analysis was left open untilcompletion of data collection and critical appraisal. If

the quantity and quality of studies were judged to beinsufficient for this, synthesis of results would be madeby qualitative methods only.

Reporting resultsTo ensure the results of this study were reported toa high standard, the guidance of the Preferred Report-ing Items for Systematic Reviews and Meta-Analyses(PRISMA) method, as described by Liberati et al,17 wasfollowed.

Results

A PRISMA flow diagram18 demonstrating how studieswere selected for inclusion in this systematic review canbe seen in Figure 3.

Two previous systematic reviews on CBCT imagingwere eligible for inclusion in this review.3,5 No ran-domized controlled trials were found during the litera-ture search. Of the 22 other full-text articles included inthe review, 10 studies looked at the effect of altering thecurrent,19 – 28 6 studies at altering kilovoltage19,20,23,24,26,27

and 18 studies at altering exposure timefactors19,21,22,24 – 27,29 – 39 (some studies looked atmore than one exposure parameter, so this total

equals .20 studies). One study40 investigated thecombined effect of current and exposure times onimage quality by altering mAs values.

Only four studies undertook any form of dosemeasurement,21,24,29,31 and just two studies performeda power calculation to identify a suitable study size.33,34

A single study26 was performed in vivo; all the remain-ing studies were in vitro. 5 different types of referencestandard were described across the 11 studies whichmeasured diagnostic accuracy.20,25,27,29,30,32 – 34,36 – 38

In addition, of these 22 studies, 17 studies reviewedhow altering exposure parameters affected the imagequality of scans produced for specific diagnostic tasks(Table 1), while 5 studies looked at a range of CBCTexposure protocols which could have been used forseveral diagnostic tasks.19,23,29,31,40

Across the total 22 studies reviewed, 23 differentnames were given for CBCT machines used in the re-search. At least 19 different CBCT models were used,

produced by 10 different companies, and the detailsprovided by 3 studies were inadequate for exact ma-chine model identification.25,32,33 It is worth mentioningat this point that the use of different names for theCBCT is likely to cause confusion and make optimi-zation more difficult for all operators.

Each of the full-text studies reviewed were evaluatedand assigned an overall GRADE value (Table 2). Onestudy, by Sun et al,41 had to be excluded as it could beevaluated only by its English abstract. This study waswritten in Chinese, and it did not prove to be feasibleto translate the complete text. The abstract stated thatthe study looked at the impact of altering exposuretime on image quality. There was not enough infor-

mation in the abstract of the study to be able to enableits fair evaluation and therefore assign a GRADEvalue.

The results of the two systematic reviews includedhad different outcomes. De Vos et al3 stated that therewas no evidence-based research at all in the area of radiation dose and image quality, while the EuropeanCommission SEDENTEXCT project5 reported thatthere was evidence that certain exposure parametershave an impact. However, both reviews agreed thatmore evidenced-based research is needed and that con-ventions on machine specifications and how methodsare described in articles need to be established.

In nine studies, altering the exposure parameters onthe CBCT scanner(s) being used had no impact on thediagnostic accuracy of, and/or pathology detectionin, the resultant images for the diagnostic task beinginvestigated.23,25,30,32 – 35,37,38,40 This conclusion wasalso supported by the English abstract of the studyperformed by Sun et al.41 Neves et al36 went so far asto specify the scanning protocol they believe gives thelowest radiation exposure while maintaining di-agnostic quality; however, they also suggested thatthe position of a particular pathology, in their studyroot resorption, may have an impact on its detectionat lower exposure parameters.




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The results of Lofthag-Hansen24 were mixed. Reducingscan times by using 180° rotation produced images of diagnostic quality for maxillary implant planning but notfor mandibular implant planning or periapical diagnosis.

When reviewing the impact of different exposureparameters on implant planning scans, Dawood et al26

cautioned that while altering exposure parameters had noimpact on two-dimensional images using the MoritaF170 Accuitomo CBCT machine (J. Morita Mfg. Corp.,Kyoto, Japan), they may affect the image quality of reconstructed three-dimensional models which aresometimes needed for this diagnostic task. However, theoutcome of the study by Vandenberghe et al27 demon-strated that this might not necessarily always be the case.

Ludlow and Walker21 were the only authors to pro-duce tables of their radiation dose and image qualitydata for each diagnostic task and scanning protocolthey considered. They suggested that clinicians andoperators make their own decision on which scanningprotocol to use, based on clinical factors including thediagnostic question to be answered and the size and ageof the patient. Bechara et al39 also encouraged case-by-case decision-making on exposure factors, as they foundthat when imaging endodontically treated root fracturesusing a 360° as opposed to 180° rotation did not im-prove sensitivity but did improve specificity by reducingartefact, which could potentially reduce the number of patients having to undergo unnecessary treatment.

Figure 3 PRISMA flow chart for this study. Adapted from Moher D et al18 with permission.




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The four articles which recorded radiation dosemeasurements each did so in a different way and ac-knowledged that it was difficult to do this accuratelyand/or in a cost- and time-effective manner owing tovarious methodological limitations.21,24,29,31

A summary table giving more details about the

methods used in, and findings of, each reviewed publi-cation can be found in Table 3.

In four of the studies,19,20,29,31 investigating the effectof different exposure parameters on CBCT imagequality was not the main aim of the study. Some basicinformation relating to these effects could be obtained,however, from the patterns of data in tables and graphs.These studies contradicted each other, with two studiesdemonstrating that image quality always declined whenexposure parameters were reduced,20,31 and theremaining two studies demonstrating that it did not.19,29

The only other study outcome which suggested thatreducing exposure parameters consistently affected im-

age quality was by Parsa et al.

22

Every study had used different methods and materialsto produce its results; this made comparison and anal-ysis difficult. Nevertheless, many authors suggest pa-tient dose reduction is possible without reducing imagequality. However, many authors also suggested thattheir results can be used only for the specific diagnostictask(s) on the specific model of the machine which theyinvestigated, and that further research isneeded.21,22,24 – 27,29,30,32 – 35,40 In addition, the studiesreviewed here have found it difficult to measure radia-tion dose from CBCT scans accurately.

Discussion

It is important to note from the outset of this discussionthat factors other than the ones investigated in this lit-erature review, such as the size and position of field of view and the patient being scanned, have a significantimpact on CBCT dose optimization. However, the aimof this literature review was to look specifically at theimpact of altering kV and mAs on CBCT dose opti-mization. Therefore, when considering kV and mAs,within the limitations of the studies reviewed, the an-swer to the research question asked at the beginning of

this review is “yes”. It is possible to reduce radiationdose to patients undergoing dental and/or maxillofacialscans without causing a detrimental impact on imagequality, and therefore diagnostic accuracy, by alteringexposure parameters on CBCT machines. However, theresults could not be generalized beyond models of

machines and/or diagnostic task(s) investigated in eachstudy, and there were several serious limitations tomethods which increased the potential bias of thestudies reviewed. These limitations are described in thefollowing paragraphs.

Most of the articles reviewed were in vitro studies,meaning that the evidence available to operators is lowin the hierarchy of evidence;42 Lofthag-Hansen24 alsofound this during her literature search. A higher stan-dard of evidence in this area could potentially beproduced by an international radiation dose andvisual-grading study,24 led by an organization such asSEDENTEXCT, in which images of real patients are

randomly selected and a range of different exposureparameters, CBCT machines and diagnostic tasks areinvestigated. However, such a study would take a hugeamount of time and resources in many dental-imaginginstitutions; so, a more realistic prospect to improve theevidence available would be to try to reduce the amountof bias in current study methods.

Where diagnostic accuracy was measured, referencestandards were not consistent or reliable across studies,and investigation methods were wide ranging and var-ied, both increasing potential bias and making it im-possible to compare accurately the performance of different CBCT systems. However, this problem is notnew. De Vos et al3 designed a list of CBCT scanner

parameters which should be recorded if it is used ina scientific study and the European Commission5

stated, “it would also be useful if a valuable standardbattery of tests using a standard commercially availablephantom were prospectively adopted so that compar-isons could be made between the dimensional accuracyof different models”.

As none of the articles reviewed have recorded all theparameters De Vos et al3 suggested, or stated they wereusing a method and phantom prospectively agreed andadopted by CBCT specialists, it would appear that thesesuggestions have not yet been adopted. It is the opinionof the authors of this article that the quality of evidenceproduced would increase if standard methods were al-ways used and all CBCT scanner parameters recordedin the literature.

Table 1 Number of studies that looked at specific diagnostic tasks

Diagnostic task Number of studies

Implant planning 722,24 – 27,32,37

Simulated root resorption 234,36

Orthodontic treatment planning 221,30

Periapical bone loss 135

Periapical diagnosis 224,33

Post-operative implant assessment 120

Impacted third molars 128

Temporomandibular disorders 138

Simulated root fracture 139

One study24 investigated the impact on periapical diagnosis andimplant planning; so, the table total equals 18 studies not 17 studies.

Table 2 Methodological quality of the studies included in thissystematic review according to overall Grading of RecommendationsAssessment, Development and Evaluation (GRADE) value

Overall GRADE value Number of studies

High 15

Moderate 619,21,24,31,34,40

Low 123,20,22,23,25 – 28,32,35,38,39

Very low 529,30,33,36,37




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T a b l e 3

S u m m a r y t a b l e o f s y s t e m a t i c

r e v i e w r e s u l t s

S t u d y

A i m s

S t u d y s i z e a n d p o p u l a t i o n

E x

p o s u r e f a c t o r s

a l t e r e d

E q u i p m e n t u s e d

R e f e r e n c

e

s t a n d a r d

O u t c o m e s

O v e r a l l

a s s e s s m e n t o f

s t u d y q u a l i t y

K w o n g e t a l

2 3

S u b j e c t i v e l y m e a s u

r e t h e

i m p a c t t h a t a l t e r i n g m A

a n d k V h a s o n t h e

2 D

i m a g e q u a l i t y o f t h

r e e

d i f f e r e n t C B C T

e x a m i n a t i o n s u s i n g

a 1 6 - p o i n t r a n k i n g

s c a l e

a n d a d i a g n o s t i c q u a l i t y

q u e s t i o n n a i r e

3 2 c a d a v e r h e a d s ( i n c l u d i n g s o f t

t i s s u e s ) a n d 1 6 d r y s k u l l s — 4 8

r e s u l t a n t i m a g e s e a c h v i e w e d b y

3 0 o b s e r v e r s ( t o t a l o f 9 0

o b s e r v e r s u s e d f o r t h e w h o l e

s t u d y ) ; 3 0 j u d g e s t h e n

r e - o b s e r v e d i m a g e s 1 m o n t h

l a t e r ; s o , i n t r a o b s e r v e r

r e l i a b i l i t y c o u l d b e m e a s u r e d

m A

a n d k V

H i t a c h i C B

M e r c u R a y a

N o n e

G e n e r a l l y , i m a g e s t a k e n a t l o w e r

k V a n d m A s e t t i n g s w e r e

c o n s i d e r e d t o m a i n t a i n t h e i r

d i a g n o s t i c a c c u r a c y a n d b e

c o m p a r a b l e w i t h t h o s e t a k e n a t

h i g h e r e x p o s u r e p a r a m e t e r s .

H o w e v e r , t h e r e w a s l o w

i n t e r o b s e r v e r r e l i a b i l i t y , a n d

r e s e a r c h e r s s t a t e d t h e y h a d f o u n d i t

d i f f i c u l t t o d e f i n e a n d q u a n t i f y

c l i n i c a l i m a g e q u a l i t y . I t w a s a l s o

c o n c l u d e d t h a t s o f t t i s s u e s m a y h a v e

a n i m p a c t o n i m a g e q u a l i t y a t

d i f f e r e n t e x p o s u r e p a r a m e t e r s , b u t

f u r t h e r r e s e a r c h i n t o t h i s

w a s n e e d e d .

L o w

L o u b e l e e t a l

2 9

Q u a n t i t a t i v e l y m e a

s u r e

t h e i m a g e q u a l i t y a n d

r a d i a t i o n d o s e o f C

B C T

a t a r a n g e o f p r o t o

c o l s

c o m p a r e d w i t h M S C T

m a x i l l o f a c i a l p r o t o

c o l s

T w o d i f f e r e n t Q A p h a n t o m s

s u r r o u n d e d b y w a t e r ( t o

e m u l a t e s o f t t i s s u e s ) a n d a d r y

s k u l l ; f o u r d i f f e r e n t C B C T

s c a n n i n g p r o t o c o l s t e s t e d

E x

p o s u r e t i m e

i - C A T b

M e a s u r e

m e n t s

m a d e w i t h a l a s e r

s c a n n e r

T h e t a b l e s o f d a t a i n t h e a r t i c l e

s u g g e s t t h a t i n c r e a s i n g t h e

e x p o s u r e t i m e i n c r e a s e s t h e d o s e

w h i l e n o t a l w a y s i m p r o v i n g t h e

i m a g e q u a l i t y , b u t , n o d i s c u s s i o n

a b o u t h o w c h a n g i n g t h e e x p o s u r e

t i m e a f f e c t e d i m a g e q u a l i t y a n d

d o s e o f C B C T s c a n s c o m p a r e d

w i t h e a c h o t h e r , o n l y c o m p a r e d

w i t h M S C T s c a n s

M o d e r a t e

L o u b e l e e t a l

1 9

Q u a n t i t a t i v e l y m e a

s u r e

t h e i m a g e q u a l i t y o f

C B C T s c a n s a t a r

a n g e

o f p r o t o c o l s c o m p a r e d

w i t h M S C T

m a x i l l o f a c i a l p r o t o

c o l s

T w o d i f f e r e n t Q A p h a n t o m s

s u r r o u n d e d b y w a t e r s c a n n e d ;

t h r e e N e w T o m 3 G , t h r e e

A c c u i t o m o 3 D a n d s e v e n

i - C A T p r o t o c o l s t e s t e d

E x

p o s u r e t i m e ,

m A

a n d k V

i - C A T b ,

N e w T o m 3 G c

a n d A c c u i t o m o 3 D d

N o n e

N o d i s c u s s i o n a b o u t h o w c h a n g i n g

e x p o s u r e t i m e a f f e c t e d i m a g e

q u a l i t y a n d d o s e o f C B C T s c a n s

c o m p a r e d w i t h e a c h o t h e r , o n l y

c o m p a r e d w i t h M S C T s c a n s .

G r a p h s i n c l u d e d i n t h e r e s u l t s

s e c t i o n s h o w s i m i l a r r e s u l t s f o r

d i f f e r e n t p r o t o c o l s o n t h e s a m e

m a c h i n e , b u t , r e s u l t s f o r C N R i n a i r

a n d t h r e s h o l d c a l c u l a t i o n s f o r

a l u m i n i u m d o d i f f e r w i d e l y b e t w e e n

p r o t o c o l s o n s o m e m a c h i n e s

s u g g e s t i n g t h a t f u r t h e r r e s e a r c h i s

n e e d e d ( a l t h o u g h t h i s i s n o t s t a t e d

i n t h e a r t i c l e )

V e r y l o w




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T a b l e 3 .

C o n t i n u e d

S t u d y

A i m s


E x p o s u r e f a c t o r s

a l t e

r e d


R e f e r e n c e

s t a n d a r d

O u t c o m e s

O v e r a l l



B r o w n e t a l

3 0

Q u a n t i t a t i v e l y m e a s u r e

t h e e f f e c t t h a t a l t e r i n g

e x p o s u r e t i m e h a s o

n 3 D

C B C T i m a g e q u a l i t y b y

t a k i n g m e a s u r e m e n

t s

b e t w e e n p r e - s e t

l a n d m a r k s a s r e q u i r e d

f o r o r t h o d o n t i c

t r e a t m e n t s , o f f e a c h

s c a n t a k e n

1 6 l i n e a r d i m e n s i o n s b e t w e e n 2 4

a n a t o m i c p o i n t s o n 1 9 d r y

d e n t a t e h u m a n s k u l l s m e a s u r e d ;

t h r e e d i f f e r e n t p r o t o c o l s t e s t e d ;

t w o o b s e r v e r s u s e d t o m e a s u r e

r e f e r e n c e s t a n d a r d a n d o n e

o b s e r v e r f o r m e a s u r e m e n t s

f r o m C B C T i m a g e s

E x p o s u r e t i m e

i - C A T C l a s s i c b

M e a s u r e m e n t s

t a k e n d i r e c t l y

f r o m d r y

s k u l l

R e d u c i n g t h e n u m b e r o f

p r o j e c t i o n s t a k e n ( a n d t h e r e f o r e

e x p o s u r e t i m e ) d o e s n o t r e d u c e

t h e a c c u r a c y o f 3 D m e a s u r e m e n t s

t a k e n u s i n g C B C T i m a g e s

V e r y l o w

D e V o s e t a l

3

S y s t e m a t i c r e v i e w o f a l l

l i t e r a t u r e r e l a t i n g t o

d e n t a l a n d m a x i l l o f a c i a l

C B C T i n c l u d i n g i m

a g e

q u a l i t y a n d

r a d i a t i o n d o s e

P u b M e d s e a r c h e d , 3 8 0 s t u d i e s

f o u n d ; 1 7 7 s t u d i e s f o u n d t o b e

c l i n i c a l l y r e l e v a n t w e r e a n a l y s e d

i n d e t a i l

N / A

N / A

N / A

I n a l l C B C T s t u d i e s , t h e r e i s

i n c o n s i s t e n c y i n h o w a c q u i s i t i o n

p r o t o c o l s , a n d w h i c h e x p o s u r e

p a r a m e t e r s , a r e r e p o r t e d . T h e r e

a r e a l s o n o c o n v e n t i o n s o n h o w

C B C T d o s i m e t r y s h o u l d b e

m e a s u r e d , r e s u l t i n g i n

u n c o n t r o l l e d a n d

n o n - e v i d e n c e - b a s e d r a d i a t i o n

d o s e v a l u e s b e i n g r e p o r t e d .

C o n c l u d e d t h a t t h e r e n e e d s t o b e

e v i d e n c e d - b a s e d r e s e a r c h c a r r i e d

o u t o n r a d i a t i o n d o s e i n C B C T ,

w h i c h i n t u r n w i l l i m p a c t i m a g e

q u a l i t y a n d e x p o s u r e

p a r a m e t e r - s e t t i n g r e s e a r c h

L o w

S u o m a l a i n e n

e t a l

3 1

Q u a n t i t a t i v e l y m e a s u r e

t h e i m a g e q u a l i t y a

n d

r a d i a t i o n d o s e o f

d i f f e r e n t C B C T

p r o t o c o l s c o m p a r e d

w i t h

M S C T m a x i l l o f a c i a l

p r o t o c o l s

T i s s u e d o s e s m e a s u r e d u s i n g

s c a n s o f a R A N D O ®

( R a d i a t i o n A n a l o g u e

D o s i m e t r y S y s t e m ; N u c l e a r

A s s o c i a t e s , H i c k s v i l l e , N Y )

h e a d p h a n t o m . I m a g e q u a l i t y

( e v a l u a t e d u s i n g C N R a n d

M T F ) a n d a b s o r b e d d o s e

m e a s u r e d u s i n g a n R S V P

( R a d i o s u r g e r y V e r i f i c a t i o n

P h a n t o m ; T h e P h a n t o m

L a b o r a t o r y , S a l e m , N Y ) h e a d

p h a n t o m


( s c a n s t a k e n a t

d i f f e r e n t

r e s o l u t i o n

s e t t i n g s )

S c a n o r a

®

3 D

s c a n n e r e

N o n e

L i t t l e d i s c u s s i o n a b o u t h o w

c h a n g i n g e x p o s u r e t i m e a f f e c t e d

i m a g e q u a l i t y a n d d o s e o f C B C T

s c a n s c o m p a r e d w i t h e a c h o t h e r .

B u t , l a r g e v a r i a t i o n s i n p a t i e n t

d o s e a n d i m a g e q u a l i t y w h e n

u s i n g d i f f e r e n t p r o t o c o l s

d e m o n s t r a t e a n e e d t o o p t i m i z e

i m a g i n g p a r a m e t e r s . C N R a n d

M T F a r e r e p o r t e d a s b e i n g

h i g h e r , a n d g r a p h i c a l d a t a

d e m o n s t r a t e h i g h e r c e n t r a l a x i s

d o s e s , w h e n h i g h e r r e s o l u t i o n

p r o t o c o l s a r e u s e d

M o d e r a t e




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T a b l e 3 .

C o n t i n u e d

S t u d y

A i m s


E x p o s u r e f a c t o r s

a l t e r e d


R e f e r e n c e

s t a n d a r d

O u t c o m e s

O v e r a l l



Y a d a v e t a l

3 8

I n v e s t i g a t e w h e t h e r

a l t e r i n g e x p o s u r e t i m e

h a s a n e f f e c t o n

d e t e c t i n g a r t h r i t i c

c h a n g e s i n

t e m p o r o m a n d i b u l a

r

j o i n t s

1 7 d r y s k u l l s u s e d w i t h

w a t e r - f i l l e d l a t e x g l o v e s a n d

w a x a r o u n d j o i n t s t o s i m u l a t e

b r a i n a n d s o f t t i s s u e h a d 1 0 2

s i m u l a t e d l e s i o n s c r e a t e d i n

t h e m a t r a n d o m l y s e l e c t e d s i t e s .

O n e o r t h o d o n t i s t a n d o n e o r a l

m a x i l l o f a c i a l r a d i o l o g i s t

r e v i e w e d a l l t h e i m a g e s


( 1 8

0 ° a n d 3 6 0 °

r o t

a t i o n a l

s c a

n s t a k e n )

3 D A c c u i t o m o

d

T h e o r i g

i n a l

d o c u m e n

t s o f

t h e k n o w

n

l e s i o n p o

s i t i o n s

W i t h a l l o t h e r e x p o s u r e f a c t o r s ,

t h e s a m e 1 8 0 ° a n d 3 6 0 ° r o t a t i o n a l

s c a n s p r o d u c e d e q u a l l y a c c u r a t e

r e s u l t s ; t h e r e f o r e , a d e q u a t e

d i a g n o s t i c i m a g e s c a n b e

o b t a i n e d w h i l e r e d u c i n g p a t i e n t

r a d i a t i o n d o s e

L o w

P a u w e l s e t a l

4 0

I n v e s t i g a t e t h e i m p

a c t

a l t e r i n g m A s h a s o

n

C N R ( q u a n t i t a t i v e

m e a s u r e m e n t ) a n d i m a g e

q u a l i t y ( s u b j e c t i v e ,

q u a l i t a t i v e

m e a s u r e m e n t )

4 0 s c a n s t a k e n u s i n g a P M M A

p h a n t o m a n d a R A N D O ®

( T h e

P h a n t o m L a b o r a t o r y , S a l e m ,

N Y ) a n t h r o p o m o r p h i c s k u l l

p h a n t o m . C N R o f a i r m e a s u r e d

u s i n g s c a n s o f t h e P M M A

p h a n t o m . S i x r a d i o l o g i s t s t h e n

a s s e s s e d e a c h s c a n f o r o v e r a l l

i m a g e q u a l i t y a n d d i a g n o s t i c

c o n f i d e n c e f o r t h r e e c l i n i c a l

a p p l i c a t i o n s u s i n g a f o u r -

p o i n t s c a l e

m A

s

3 D A c c u i t o m o ,

1 7 0 d

C R A N E X , 3 D e

S C A N O R A 3 D e

G a l i l e o s

C o m f o r t

l

N o n e

A l t h o u g h C N R i n c r e a s e d a t

l o w e r m A s v a l u e s , o b s e r v e r s f e l t

t h a t m o s t i m a g e s w e r e s t i l l

c l i n i c a l l y a c c e p t a b l e . H o w e v e r , i t

i s n o t c u r r e n t l y p o s s i b l e t o

d e t e r m i n e d i a g n o s t i c r e f e r e n c e

l e v e l s f o r m u l t i p l e C B C T m o d e l s

M o d e r a t e

2 D , t w o d i m e n s i o n a l ; 3 D , t h r e e d i m e n s i o n a l ; C N R , c o n t r a s t - t o - n o i s e r a t i o ; D A P , d

o s e – a r e a p r o d u c t ; F O V , f i e l d o f v i e w ; k V , k

i l o v o l t a g e ; m A , m i l l i a m p e r e ; m A s , m i l l i a m p

e r e s e c o n d ; M S C T ,

m u l t i s l i c e C T ; M T F , m o d u l a t i o n t r a n s

f e r f u n c t i o n ; Q A , q u a l i t y a s s u r a n c e ; Q U A D

A S , q u a l i t y a s s e s s m e n t o f d i a g n o s t i c a c c u r a

c y s t u d i e s ; P M M A , p o l y ( m e t h y l m e t h a c r y l a

t e ) ; S I G N , S c o t t i s h

I n t e r c o l l e g i a t e G u i d e l i n e s N e t w o r k ; S I

G N 5 0 , S I G N 5 0 t h g u i d e l i n e .

a H i t a c h i M e d i c a l S y s t e m s , T o k y o , J a p

a n .

b I m a g i n g S c i e n c e s I n t e r n a t i o n a l , H a t f i e l d , P A .

c Q u a n t i t a t i v e R a d i o l o g y , V e r o n a , I t a l y

.

d J . M o r i t a M f g . C o r p . , K y o t o , J a p a n .

e S o r e d e x , T u u s u l a , F i n l a n d .

f K a V o D e n t a l G m b H , B i e b e r a c h , G e r m a n y .

g P l a n m e c a O y , H e l s i n k i , F i n l a n d .

h V a t e c h , E - W O O T e c h n o l o g y C o . L t d

, G y e o n n g i - D o , R e p u b l i c o f K o r e a .

i I m t e c P l a z a , A r d m o r e , O K .

j K o d a k D e n t a l S y s t e m s , C a r e s t r e a m H

e a l t h , R o c h e s t e r , N Y .

k S i r o n a , B e n s h e i m , G e r m a n y .

l I n f o r m a t i o n g a i n e d f r o m C o m p a r i s o n o f C B C T M a c h i n e s o n S E N D E N T X C T w e b

s i t e . A v a i l a b l e f r o m : h t t p : / / w w w . s e d e n t e x c t . e u / c o n t e n t / c o m p a r i s o n - c b c t - m a c h i n e s ? s o r t 5 a s c & o r d e r 5 M o d e l .



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Measuring effective dose with thermoluminescentdosemeters for all the tissues in the head and neck isvery time consuming and expensive, and owing to thewide range of different machines, results could not begeneralized.21,24 Therefore, international research andagreement is also needed to find a cost- and time-effective

way of reliably calculating the dose that patients un-dergoing CBCT receive so that operators can know ex-actly how altering different exposure factors will impactboth patient dose and resultant image quality. Dose – areaproduct (DAP) measurements would seem to be the mostpracticable means of representing patient dose, as thesehave been proposed for definition of Diagnostic ReferenceLevels, are readily measured in clinical situations, relatereasonably well with effective dose5,8 and, since the intro-duction of regulation 60601-2-63 by the InternationalElectrotechnical Commission in 2012, manufacturershave been required to provide a DAP measurement on allCBCT equipment.43 However, Lofthag-Hansen24 found

that the central point of the scan is not always at the centreof the clinical region of interest, and so, patient radia-tion dose measurements could be both overestimated orunderestimated depending on the area being imagedusing DAP measurements. However, this does not meanthat DAP cannot be used to assess dose-reduction strate-gies and compare the results from different CBCTequipment and/or different diagnostic tasks in dose-optimization studies.

Alternative methods of measuring dose should not bediscounted though. Recent research suggests that dose – height product could provide a more accurate alternativeto DAP measurements;44 however, further research in thisarea is urgently needed. Some have investigated possible

conversion co-efficients that may allow DAP readings tobe used to work out an estimation of effective dose.45

Programs based on the Monte Carlo simulation, such asthe one investigated by Koivisto et al,46 also need to beconsidered. These can be of value because they permiteasy manipulation of exposure variables without per-forming time-consuming experiments in the field.

Four studies19,21,31,40 used contrast-to-noise ratio(CNR) as a quantitative measure of image quality, toprovide objective data to complement subjective imagequality assessment. However, the materials used tomeasure CNR can vary; so, comparison between dif-ferent studies is difficult if the studies have used differentmaterials. Furthermore, the reliance of CNR data basedon a Perspex® (Mitsubishi Rayon Group, South-ampton, UK) – air interface can be questioned whenclinical images rely on the contrast between hard andsoft tissues. Alternatives, or additions, to CNR, such astests of spatial resolution, modulation transfer functionor other parameters, may also be important objectivemeasures of image quality. Clearly, further work look-ing at the relationships between these objective meas-urements and clinical image quality is needed.

While much research appears to have been carriedout into the impact that dose optimization has onimage quality for implant-planning CBCT scans, only

two studies,28,39 which were of low quality, have beencarried out relating to other common CBCT diagnostictasks, such as identifying the position of impacted teethor trauma, in which many patients would be youngerand so dose optimization of paramount importance.3,5

This provides a substantial issue for dental radiogra-

phers and other CBCT operators, because for suchdiagnostic tasks, there is currently minimal evidence of the impact altering different exposure parameters hason resultant scan image quality. Reducing exposureparameters may still result in a diagnostically accept-able image but could also result in an undiagnosticimage, meaning that the scan would need to be repeatedand the patient would get substantially more radiationdose than if the scan ha

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