Received:6Decembe｢2022Revised:28June2023

Accepted$9August2023

DOI;101002/acm2､14142」○URNALOFAPPLIEDCLINICALMEDICALPHYSICSRADIATIONONCOLOGYPHYSICS

Evaluationofcomputedtomographymetalartifactand

CyberKnifefiducialrecognitionfOrnovelsizefiducial
markers
HikaruNemoto''2 IMasahideSaito2 ITbshihiroSuzuki3

I

HidekazuSuzuki2

1

NaokiSano2 1ZennosukeMochizuki3 IKQjiMochizuki3 1 KOjiUeda2 1
TakafumiKomiyama2 IKanMarino2 1ShinichiAoki2 1 MitsuhikoOguri4 1
HiroshiTakahashi3

IHiroshiOnishi2'DepartmentofAdvancedBiomedical
Imagin9,Universityof"manashi,"manashi,Japan

2DepartmentofRadiologywUniversityof
Yamanashi,"manashi,Japan

3KasugaiCyberKnifeRehabilitationHospital,"manashi,Japan

4DepartmentofRadioiogyShizuckaGenerai

Abstract

Purpose:ThisstudyaimedtocomparefiducialmarkersusedinCyberKnife
treatmentintermsofmetalartifactintensityobservedinCTimagesandfiducial

recognitionintheCyberKnifesystemaffectedbypatientbodythicknessand
typeofmarke[

MethodsgFivemarkers,ACCULOC0.9mm×3mm,BalltypeGoldAnchor(GA)0.28mm×10mm,028mm×20mm,andnovelsizeGAO.4mm×10mm,

Hospital,Shizuoka,Japan

0.4mm×20mmwereevaluated.TbevaluatemetalartifactsofCTimages,two

Correspcndence

typesofCTimagesofwater-equivalentgeIswitheachmarkerwereacquired
usingAquilionLBCTscannemoneappliedSEMAR(SEMAR-on)andtheother

HikaruNemoto,DepartmentofRadiologM

UniVersityof"manashi,1110Shimokato,Chuo-citM"manashi1409-3898,Japan
Email:hnemolo@yamanashi.ac.jp

didnotapplythistechnique(SEMAR-off)Theevaluationmetricofartifactinten-sity(MSD)whichrepresentsavariationofCTvalueswerecomparedfOreachmarke[Next,5,15,and20cmthicknessofTbughWater(TW)wasplacedonthegelundertheconditionofoverlappingthevertebralphantomintheTarget
LocatingSyrem,andtheliveimageofeachmarkerwasacquiredtocomparenducialrecognition.

Results;ThemeanMsDofSEMAR-offwas78.80,74.50,97.25,83.29,and
149.64HUfOrACCULOC,GAO､28mm×10mm,20mm,and0.40mm×10mm,

20mm,respectiveIMInthesamemanneI;thatofSEMAR-onwas23.52,20.26,
26.76,24.89,and33.96HU,respectiveIMFiducial recognitiondecreasedinthe
orderof5,15,and20cmthickness,andGAO､4×20mmshowedtheberrecognitionatthicknessof20cmTW
Conclusions:WedemonstratedthepotentialtoreducemetalartifactsintheCT
imagetothesamelevelfOrallthemarkersweevaluatedbyapplyingSEMAR.

AdditionalIMthefiducialrecognitionofeachmarkermayvarydependingonthe
thicknessofthepatient'sbodMParticularIMweshowedthatGA0．40×20mm

mayhavemoreoptimal recognitionlbrCyberKnifetreatment incasesofhighbodilythicknessincomparisontotheothermarkers.
KEYWORDS

CT-artifacts,CyberKnifesystem,fiducial,imagerecognition,markers－－－－■■‐■■一一一＝－－－－－－－－■■■■＝■■－■■■■一一一■■－－－－■■---■■■■一一一■■■■＝＝■■－－－－－－－－－■■一一一q■F一一一■■一■■－－－－－－■■－1■、■■一一■■－－－■■■■－－－■■－－－－－－－－－－－－

ThisisanopenaccessarticleunderthetermsoftheC｢eativeCommonsAttribulionLicense,whichpermitsuseidistributionandreproductioninanymedium,provided
theoriginalworkisproperlycited,@2023TheAuthors.qmumaﾉofAPP"edC"hicaﾉMeMca/PhysjCspublishedbyWileyPenodicais,LLConbehalfofTheAmencanAssociationofPhysicistsinMedicine
JApp/CInMedMys.2023;el4142
htips.//doiorg/101002/acm214142

wileyonlinelibrarycomﾉi｡urna,/acm2 1 1oflO

"LMEDICALPRYSrs
1

INTRODUCTIONNEMOTOETAL

abdominalregion､13FOrthesereasons,inordertoselecttheoptimal fiducialmarkenit isnecessarytoevaluate

Stereotactic body radiotherapy (SBRT) using
CyberKnife(AccurayISunnyvale,CalifOrnia,USA) is
effectiveintreatingtumorsthatareaffectedbyphysiologicalmovementsderivedfromrespiration, rectal
gasmovement,andurinevolumeinthebladderandtreatment.Theneedlesizeusedtoimplanteachfiducial
markeris25andl8G,respectivelyiTWonovelGAfiducialsizes,GAO.4mm×10mmandGAO.4mm×20mm,

haverecentlybeenint1℃ducedfOrCyberKnifetreatment.
ThenovelsizeGAisthickerthantheconventionalsize

GA0．28mm×10mmandGAO､28mm×20mm,

whichmayimprovefiducialrecognition.Additionallybthe
needlesizeofnoveIGAis22G.ThenovelsizeofGAO､4×10mmandGAO.4×20mmisthinnerthanACCU-

LOC,makingthemlessinvasive.Howeventherehave

beennoreportsevaluatingGAO.4mm×10mmand
GAO.4mm×20mm.TherefOre,thisstudyaimedtocomparethestrengthofmetalartifactsinCTimagesandthe
effectsofpatientbodythicknessonnducialrecognition

inCyberKnifetieatmentfOrtwoconventionalsize(GA0.28mm×10mm,20mm)andtwonovel-sizedGAs(GAO.4mm×10mm,20mm)withastandardcylinder
markeMACCULOC(0.90mm×3.0mm).

planningCTimagesusingtemplatematching.4,5Registrationaccuracybetweenx-rayimageswithfiducial

markersandDRRsisaffectedbyhowaccuratelythesoftwarecanidentifythelocationofthemarkers,thatis,

fiducialrecognition.Therefbre,severalsizesandshapes
ofnducialmarkersareuseddependingonthetumor
Iocationandthepatient'sbodythickness・Thesizeand
shapeofthemarkeraffectfiducial recognitioninthe
TLSandthestrengthofmetalartifacts incomputed

2 IMATERIALANDMETHOD
2､1 ICharacteristicsoffiducialmarkers
Figure l presentsthecharacteristicsof themarkersevaluatedinthisstudMTherearetwofOmethods

tomography(CT)imagesfbrtreatmentplanningSpecif

of implantingGAs in thebody: ball- andstraightshaped.Aball shape isfOrmedby insertingacoil
whilemaintainingthepositionof theneedie.Though

icalIMtheuseof largerfiducialmakershasthepotential

theuncoiledlengthofGAislOor20mm,thediam-

toimprovefiducial recognitionwhilealso increasing
metalartifacts.Fortreatmentplanning,metalartifacts
makeitdifficultioaccuratelydelineatethetumorand
normaltissueP-9Theseartifactsalsohavethepotential

eterofbail-shapedGAbecomesapproximately5or
6mmonce implanted.Howevenastraightshape isibrmedby insertingthecoilwhilepullingtheneedleout.Themaximumlengthofrecognitionregionon

topropagatetodensityassignmenterrorsanddose

TLSis8.0mm.TherefOre,fiducialmarkerslongerthan

calculationerrors.10-12Furthermore,implantingfiducial

approximately8mmmayhavebeenmisrecognizedmarkers inpatientswithhigherbodythicknessor in
Iocationswheretheyoverlapwithboneorotherhighly

absorbentmaterialmaydecreasetheircapacityfOr

ACCULOC(090mm×3mm),whichisacylinder-type

Therefbre, fiducialmarkers implantedusingthinnerneedlesarepreferable･Pateletal recommendedusing

goldmarkerwithpharmaceutical approval (PharmaceuticaIAffairsRegulatoryinJapan) fOrCyberKnife

thinnerneedleswhenimplantingfiducialmarkeratthe

treatment.

⑳宮⑤唾ｃくＥ二食色弓と皇居層七壱二便匡邑置戸一晶蓉ちぐにＦｃ一三岳呈夛Ｆ雇念基

nducial recognition. lnaddition,thesefiducialmarkers
areimplantedusinganeedle,whichishighlyinvasive
andcancausepneumothorax,bleeding,andinfections.

bytheCyberKnifesystemjasthestraight-shapedGA
waslOand20mm(>80mm)ontheTLS,onlyballshapedGA(0.28mm×20mm,0.28mm×20mm,
0.4mm×10mm,and0.4mm×20mm)wereevaluatedinthis､ud)AThesegoldmarkeIswerecomparedwith

宮望Ｆゴー、ＫＥ弓旨臣、．ｒ一己毎匡迷昌二ＥＣ、ご肖卜こ卜し』‘し、帥匡置』ｎ．一覆畠匿〆ｃ諄色一二ｃ雪唾壱』一石“舎旦己冨』』目偏二劃昌芋筆言、龍円僧憎ｐｆＰ…ｌ５ｉ‐‐・・‐‐叩叫ｃ二弓一意》〆菖】一二肩ｒ・邑角筐『亜』ｃ常『巨肩啄阜一宮鉱Ｆこき

x-rayimagesinvoIvingfiducialmarkersareregisteredto
digitallyreconstructedradiographs(DRRs)derivedfrom

Manycommercialfiducialmarkersarecurrentlyused.
TheGoldAnchor(GA)(NaslundMedicaIAB,Huddinge,
Sweden)andACCULOC(CIVCOMedicaISolutions,
Kalona, IA,USA)arecommonlyused inCyberKnife。とｆＣ

methodisunsuitable.3Whileusingfiducialtracking,gold
fiducialmarkersthatarevisibleunderx-rayimaging
areoftenusedtoalignthetargetduringthecourse
oftreatmentusingTargetLocatingSystem(TLS)TLS
consistsofanorthogonalx-rayimagingsystem,andthe

recognition,metalartifacts,andthesizeofthemarker's
needle.

ここ雪一仁・一亡《Ｐ卜、辱喰二宮卜

hasbeen introduced inglobal institutions.1'2There
aretwo irradiationtechniquestotreat tumorsusing
CyberKnife: (1) irradiationsynchronizedwithnducial
markers implantedinthebody(fiducial tlacking)and(2)markerlessdynamicbodytrackingirradiationusingalignmentx-rayimages,that is,XsightLungtracking
orXsightSpineTracking. Thismarkerlessdynamic
bodytrackingmethodrequiresthat thetumorhave
sufficientcontrastrelativetothesurroundingregion;fOr
example,tumor locatedanywhereinthespineornear
thespineandIocatedintheperipheral lungsandapex
lungregion･Howeverthefiducial trackingmethodcan
beusedfOrsofttissuetargets,suchastheprostate,pancreas,livenandlungtumors,whereintheXsightlung

andtake intoconsiderationfactorssuchasfiducial

こ．ＥＣ毛弓一ｃ唇仁信仁冨ｃ言二二一でソ邑語岫凸国・弓“Ｆ呂弓』ロ”風・ロ・もこａ芝君代唖

1』卜。

」○URNALOFAPPLIEDCLINICALACCUIDC

GoldAnchor(CIVCOMedicalSolutions，

Fiducialmarker’(Nash!ngMedicalAB,HuddingC・Swedcn)
ｑ 『 ９ ４ 『 ‐ ■ ｑ 皿

walcrcquivalenlgCl

岸

＄

う，

，

三申＝

ＣＩ、ｑＤｒＨ

鍵

Fiducialmarkersin

-＃
I

アー
ーー

一

Coildiamcter(mm)

の0．90

の0．28

①0．28

⑳0．40

①0．40

Coil length(mm)

3．0

10．0

20．0

i0，0

201）

NeedleWG)

18

25

25

22

22

Gold(99.S%)Gold(99.5%)

Gold(99.5%)

Gold(99.5%)

Iron(0.5%)

Iron(05%)lron(0.5%)

Iron(05%)

Composition

Gold(nmi℃thal199.99%)

Ｉ

Kalona,IA,USA)一－－口ー

FIGURE1

Characteristicsoffiducialmarkersevaluatedinthisstudy

where,theX'representstheCTvalueofvoxelsthat
exceedthethresholdHUvalue,"representstheavers
ageCTvalueofalIvoxelsandNrepresentsthenumber
ofvoxelsinanalysisregion･Therefbre,MSDrepresents
theSDoftheCTvalueswithintheanalysisregion.

2．2IEvaluationofCTartifacts

2.21 IAcquisitionandreconstruction
protocolTheMSDwascalculatedonallaxialsIices,including

marke[First,CT imagesofawater-equivalentgel(50×50×25mm,cube-shaped),whichhadeachmarker implanted,wereacquired.AIICTimageswere
acquiredusingAquilionLBCTscanner(CanonMedical
SystemsCorporation, Japan)withthefbllowingsettings:120kM250mA,125mAs,1.0mmslicethickness,
512×512pixeIsandtheCTDIvoIwas16．6mGMTb
evaluatetheeffectofdifferentreconstructionalgorithms
oneachfiducialmarkemCTimagesbreachmarker
werereconstructedusingthefOllowingtwotypesof
reconstructionalgorithms: imageswithsingle-energy
metalartifactreduction(SEMARiCanonMedicalSystems,Japan)applied(SEMAR-on)andimageswithout
applyingSEMAR(SEMAR-off).TheSEMARalgorithm
canbeusedtoreducemetalartifactsusingfOrward
prqection,backwardprOjection,andsubtractingsinogram.PreviousstudiesdescribedtheSEMARalgorithm

fiducialmarkers,andthemeanMsDwascomparedmreachfiducialmarkel:Tbexcludepixelsbelonging
tothemarker itselfathresholdof250HUwasusedtoeliminatethesepixelsfromthecalcuiationofMsD.
Figule3k-oshowstheregionsofCTvalues>250HU
mreachmarkerasmaskimages.Welch'sILtestwas
usedtocompareMsDbetweenSEMAR-onimagesand
SEMAR-o什imagesandbetweeneachGAandACCULOC.TheseanalyseswerepermrmedusingMATLAB
2021bsoftware(Mathworks,Natick,MA,USA)
2．3IEvaluationofthefiducial

recognitionofCyberKnibsystem

一隅

MSD [HU]=

ｐＯＯｇ

Ⅳ石ソ全司

１

１

ThemarkersizeintheCTimagewasapproximately
10pixels･Therefbre,CTartifactswereanalyzedina
61×61pixelaxiaislicecenteredatthecenterofgravitycoordinatesofeachmarke[~Ibevaluatea､ifacts,thestandarddeviation(SD)ofCTvaluewasusedasametricfOrartifact intensity(MsD)definedbyEquation(1)wascalculatedfOreachnducialmarkel:Inthisstudybwe
definedMSDas,

IXﾉﾉｰ〃|2(1)

ThefiducialrecognitionintheTLSibreachmarkerwas
usedtoevaluatetheaccuracyofthefiducialtrackingof
theCyberKnifesystem.AIICTimagesofeachfiducial
markerwereacquiredusingOptimaCT660(GEMedical
Systems,Milwaukee,WI,USA)withthefOllowingsettings:120kM400mA,120mAs,1.25mmslicethickness,
and512×512pixeIs,andtheCTDIvoloftheabdomen
protocol isapproximately23.25mGMDRRimageswere
generatedusingCTimagesinatreatmentplanningsystem,CyberKnifeMultiPIanTPS(ve[3.2.0,AccuiaM
Sunnyvale,CalifOrnia,USA)fOreachfiducialmarke[FOrmarkerpositioning,templatematchingbetweencropped
imagesreconstructedfromDRRonTLSandliveimages
fromthesystemwasperfOrmed･TheTLSisaPCwith
digital imageprocessingsoftware,whichprocessestheradiographicimagesfi･omthenat-paneldetectors.'6The

ロ呂旨β］ｃ巨爵呂倫吃戸Ｌ二二二⑫ｒ一宅特産『望←ｃ一一Ｅ侭睦ｃＰ潭唾倫蒼」影昌二匿暉ひ唐命暁こぐ畠邑侭自己哩室晨藍でで』Ｅ色口冨ｒ『暉畦こぐＨＦＣ君胃二昌彦ｒ

2.3.1 I0bjectiveevaluationoffiducial
recognitionindetai1.14,15

2.2.2I0MectiveevaluationofCTartifacts

昌昌〕‘零冨吃電心

TheCTartifactswereevaluatedわreachfiducial

ご口院Ｌｃ乏画臣ｃ睡自偏巨属Ｃ旨冒罫笥リミロＥて程』，唱色色‐Ｄ乏晨、翼竜Ｃ一冒巨ｃＥ－とＤ』どこ卜壷昌ニト。』半ロェトｃｋｒｃ虐二登惹」掌七三一。弓髭偏ピニＬ室差一馬ｒ宰昌皇軍ｃ曽一ご畠ごミト色卜些。し仁代言肩一畠二軍ＥＥ〆ｃ二仁一二色差趣き芦壱苧MEDIcALpHYsIcs_L聖型』し卜。

JOURNALOFAPPLIEDCLINICAI
NEMmoETAL

些型-LMEDIcALpHYsIcs
pixelsintheanterior-posteriomsuperior-inferiol;andleftrightdirectionsfromthecenteroftheselectedfiducial
markenrespectivelYThepixelsizeofbothtemplateandtiontotheabovesettings,albughWaterPhantom(TW)(KYOTOKAGAKUCorporation,Japan)consistingof30×30×10cmwater-equivalentrectangularvaluedisplayedontheTLSwasusedtoevaluatethemateriaIswasplacedonawater-equivalentgeltoevaluatetheeffectofpatientbodythicknessonfiducial

fiducial lecognitionofthefiducial tracking.Theuncele
taintyvaluewascalculatedbetweenthetemplateimage

imageswereacquiredunderthreedifferentconditions:recognitionfOreachmarker (Figure2b-d).The live

andliveimageusingthesimilarityindex,zero-means

5,15,and20cmwiththefOllowingimagingacquisi-

normalizedcross-correlation(ZNCC),fbraregionof
21×21pixels,whichincludedafiducialmarker;Thus,

tionparameters:120kM100mA,100msandl30kV
100mA,100ms;thewateFequivalentthicknessofthe

theevaluationoftheZNCCregionincludednotonly
thebodyofthefiduciaimarkerbutalsothesurrounding

approximately9.55,24.42,and31.34cm,respectively

anatomynearthefiducialmarke[TheZNCCwascalculatedusingtheintensityvaluebetweenthetemplate

TWontheaxisfromthemarkertotheA-camerawas

valuewasdennedbyEquation(2).

signed-ranktestwasperiOrmedonthemeanunceF

where,(2)

酬j,,(IDRR(x'-xjy'-y)‐応)(ILiv､x',y')-"ﾉⅣcc(x,y)=2

似咋べ（IDRR(x'-x,y'-y)-")'Vzﾙﾉﾙ(x',y')-ILive）－

taintyvalueoftheACCULOCandeachGAfOreachconditiontoevaluatethenducial recognitionofeach
markeK

3

IRESULTS

3.1ICTartifacts

2.32ILiveimageacquisitionp｢oximatetothemarke[Figure4shows themean

三岳房巨ｃ弓ｒ『侭崖呈く伝〆亡冨二二Ｃ『万ｒ石昌一

paringtheliveandDRRimages.Thepositioningof

placedonthetreatmentcouchwherethemarkeroveIB賑Ｃ之屍冒』啄色巳迂lapswiththevertebral phantomatoneof thekV
prqectionangles.Next,tenliveimageswereacquired
fOreachmarkerusingtheCyberKnifesyrem,andthe
averageuncertaintyvalueswerecalculatedbycom-

Figure3showstheCTimagesintheaxial sIicefbr
eachmarkenreconstructedusingtwotypesofalgorithms:SEMAR-onandSEMAR-off lnFigure3,highfrequencystreakartifactsareobservedaroundthe
marker intheACCULOCof (f).Howeveh intheGAof(gJ), lowfrequencystreakartifactsareextensively
observedinadirectionalfashion,whilehighfrequency
reakartifactsarepartiallypresentinaparticulardirectionlnseverecaseslikeO),metalartifactscompletely
obscuretheadjacentwaterequivalentgelregion. lnthe
SEMAR-onimages,thestreakartifactswereobserved
asshowninFigure3a-eihowevel;theirintensitywas
markedlymitigated incomparisontotheSEMAR-off
imagesshown in(fJ).ThissubstantiallyamelioIated
thediscernibilityof thewater-equivalentgel region

WhentreatingabdominaltumorsusingtheCyberKnife(G4)system, fiducialmarkersoftenoverlapwiththevertebralbone.TherefOre,thisstudyevaluatedfiducial
recognition intheabdominal regionunder theconditionthat thevertebralphantom(AA/icelnc.,Tbkyo,
Japan)overlapsthenducialmarker inTLSFigure2ashowstheexperimentalsetupusingavertebialphantomandwater-equivalentgeIswithamarkeKFirst,
water-equivalentgeIswitheachnducialmarkerwere

色１代ｃ言仁呂這冨些ご言ゴー傭）〆苫二君君ｒ一口『畠く、戸色吋車匡訂畝こ』匡睦乎〆」湧畠呂昌

TheﾉDRRandﾉLjverepresentsintensityvalueinaDRR
imageandliveimage,respectivelybTheZNCCalways
fallsintherangeof-1tol･AZNCCvalueoflindicates
thatthetwoimagesarecompletelymatched･Ingeneral,
anuncertaintyof40%istheclinical thresholdibrthe
CyberKnifesystem.

ｒ・弓酉匡■】Ｃ弓一こｇご篭』トヒいい｝し硯倫呂肩二倫冨邑与色昌ＥｒＣ邑匡】二ｃ回し一二二℃“ミロ『ｇ南］・隼冨、蓮ＥＣ

Uncertainty (%)=100－ﾉⅣcc(x,y)℃屋号。こく冒冗と戸Ｌ

imageand liveimage．Subsequentlyl theuncertainty(Figure2b-d)StatisticalanalysiswaspelfOrmedonthe
measureduncertaintyvaluesusinglBMSPSSStatisticsve[24software(IBM,Armonk,NY;USA).AWilcoxon

弓』弓‐…・』宕倫ニロニ巴揖）・至筥侭亟壺Ｃ二時仁ＣＥｐｃ』ここと睡喰』邑卜Ｌ４←４トロ瞳〆《屑liveimagesisapproximately0.4mm,andthemaximum
lengthofrecognitionregionis8.0mm・Theuncertainty

markersandthevertebralphantomsweremadetobe
asidenticalaspossibleusingavisiblelaseIz Inaddi-

ｇ令戸」こ手ミニ』Ｃ陛酋、ここＣ冨一雪乞でtemplateimagefiomDRRimagewascroppedbylO

NEMOTOETAL

しｆＣ

JOURNALOFAPPLIEDCI INICAl

－－

■

(b)

(a)

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5cm

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FIGURE2 Expenmentalset-upofeachfiducialmarkenvertebralbonephantom,andTbughWaterPhantom(a)Ariangementof
watersequivalentgelwithinsertednducialmarkerandstaticphantom(vertebralbone).Thepositionofeachnducialmarkerwasoverlappedwith
thevertebralboneinTLS.(b-d)TWPhantomwasplacedonwaterequivalentgeltoevaluatetheeffectofpatientbodythicknessonfiducial

notshowstatisticallysignincantdifferencescomparedtothatofACCULOC(p=008-0.426).AdditionallyIthe

MsDfOralISEMAR-onimageswasreducedcomparedtothatofSEMAR-offimageswithstatisticallysignificant
differences(P<005).

3．2IEvaluationofthefiducial

respectivelyTheMsDforGAO.28mm×10mm,GA

recognitionoftheCyberKnifesystem

O､28×20mm,andGAO4×10mmdidnotshow

Figure5showsliveandDRRimagesibreachmarker
acquiredusingtheTLSoftheCyberKnifesystem･AII
markerscouldbevisuallyrecognizedintheliveimage
andDRRimages intheconditionofoverlappingthe
vertebral bone･TablelandFigure6showthemean
uncertaintyvaluesandtheirstandarddeviationsfOrlO
liveimagesfOreachmarkeracquiredunderthreedifb

20.26,26.76,24.89,and33．6HUfOrACCULOC,GA

ferentconditionswithTWthicknessesof5, 15,and

0.28mm×10mm,GAO､28mm×20mm,GA

0.40mm×10mm,andGAO.4mm×20mm,respec-

20cm,respectiveIMoverlappingthevertebralphantom.
Foreachfiducialmarkennduciai recognition inTLS

tiveIMForSEMAR-onimages,theMsDofaIIGAdid

decreasedwithincreasingTWthickness.FOraTW

毛でstatisticallysignificantdifferencescomparedtothatof
ACCULOC(p=Q14-0.41).HoweventheMsDfOrGA
O､4×20mmwassignificantlyhigherthanthatof
ACCULOC(p=004).TheMSDfOrACCULOCwas
Iower thanthatofallGAexcept0．28mm×10mm
sizeintheSEMAR-offimages.ConcerningSEMAR-on
images,themeanMsDofall axialsliceswas23.52,ｒ』ｃ『邑壺電』Ｃ『菌匡一偏呼Ｃ一こり⑤．戸Ｌ、〆也亘二侭二倫呼Ｌ『、晩こぐ偏邑肩色。〕

LOC,GAO.28mm×10mm,GAO.28mm×20mm,
GAO.4mm×10mm,andGAO.4mm×20mm,

二５Ｆ亡二亡Ｏ彼ｃ二Ｅ二』但雲シ』ｃ弓哲ご呈侭》ＰＬ

MsDfOreachmarker inallaxialslicesincludingthe
fiducialmarke[TheMsDof theCTvalueswascalculatedbr the61×61-pixel regionexcludingthe
regionofthemarker (>250HU).RegardingSEMARoff images, themeanMsDofall axial sIiceswas
78.80,74.50,97.25,83.29,and149.64HUfOrACCU-

ｃ南色【】きく客頂く“眼ＣＱ

recognition.TWthicknesswasfOllowingsetting:(b)TW=5cm(c)TW=15cm,and(d)TW=20cm.

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4

1

DISCUSSION

Thefiducial recognitionofmarkersonTLSmaybe
significantlyreducedwhenimplantedfiducialmarkers
overlapwithboneorotherhighx-rayabsorbentsinthe
bodylnthisstudyiwecomparedfOurtypesofGAsand
ACCULOCfOrCTartifactsandfiducial recognitionon
TLS,lbrdifferentpatientbodythickness.
Fiducialmarkersarecommerciallyavailableinavarietyofdiametersand lengths. Ingeneral, the larger
thesizeofthemarkerithebetterthevisualevaluation

maybegenerated･Thegenerationofstrongmetal
artifactscansignificantlyaffectthecontouringofthetumorandorgansatrisk8､9anddosecalculationsibr
treatmentplanningledtoreporteddoseoverestimation
rangingfrom9to39.8%inheadandneckcancertreat-

theimpactonthedosedistributionmaybelowerthan
thereportede｢『o[ThisisaconcerntobeaddressedfOr
fUtureinvestigations･TherefOre,itisimportanttoreduce
themetalartifactscausedbynducialmarkers inthe
CyberKnifesystem.OurresultsshowedthatinSEMERoff images,theMSDfOrGAO､28mm×10mm,GA
O､28×20mm,andGAO､4×10mmdidnotshow

statisticallysignificantdifferencescomparedtothatof
ACCULOC(p=0.14-0.41)HoweventheMsDfOrGA
O,4×20mmwassignincantlyhigherthanthatofACCULOC(p=0.04)IntheSEMAR-onimages,allGAsand
ACCULOCshowednostatisticallysignificantdifference
inMsDTherefOre,theresultssuggestthattheSEMAR
aigorithmhasthepotentialtominimizetheintensityof
artifactscausedbyeachmarkertoanequal level.Brook
etal.evaluatedsoftwaretoimprovethetumorvisibilityin
thevicinityofnducialmarkersinspectialC~I;whichisdifL

mentusinglinearaccelerato[17-20Regardingthedose

ficulttouseinradiationtherapy2'Huangetal.suggest

overestimation,theareainwhichtheCTvaluesareinnu-

thatartifactreductionallowsmoreconfidentcontouF

encedbyartifactsofthenducialmarkerislimited,thus

ingofstructuresPHence,inthefuture,fiducialmarkers■

Ｅ」〆昌臣喧雇伊Ｅ便娠Ｃく塁・壽侭ｃｐ哩二肩と毛迄』晨宕毎届Ｆ｝暉営乏侭ｒ色置冨冨Ｃ【ＦＦ旨皇andfiduciai recognitionjhowever;strongmetalartifacts『ご弓”：．…．…・・‐・・〉芝』届吹冶こ】号仁ｃＥ戸』・』ここ卜『医食邑】ト。←４－＆恥。虻〆ｃ厘呂哩一肩畠】胃二Ｆ迂望一高〕戸』再旨】届ｒ】弓毎三哩色二一臣。『匡署卜ごトレ』，、

120/100

p-value

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一一

句surroundingstructures,anddosecalculationsshouldbe
evaluatedinmoredetail.

MEDICALPHYSICSl聖型

ingonthepersonperfOrmingtheimplantation,which

under theconditionsofdifficuit-to-tlackmarkers indosecalculationunderconditions,whereinthemarker

theCyberKnifbsystem.5HoweveEnostudyhasevaluatedfiduciai recognitionof thenovel-sizednducial

movesowingtothephysiologicaldisplacementatothertreatmentsitesisrequired･Third,wedidnotevaluate

markernewlyavailablefOrCyberKnifetreatment･ In

theeffectofSEMARonDRRimageandfiducialrecog-

addition,theuncertaintyvalueiscalculatedfOracon-

nitionintheCyberKnifesystem.Fourth,usingSDalone
toevaluatemetalartifactsinCTimagesmaynotcompletelyevaluatetheartifactseveritMAndweusedthe
ROl thresholdingmethodtoeliminateregionsofthemarkerbodyfiomtheanalysisregion･Thisstudyused
SDasasimpleandquantitativemeasureofartibct
severitythatcanbeeasilycomparedacIossdifferent
markers.Dongetal usedartifact indexandZhang
etalandMeyeretal usedmotmeanssquareerror

nned21×21-pixelregion,includingthefiducialmarker;
and isafbctedbythex-rayattenuationcoefficientoftheanatomicalstructuresnearthemarkel:Conse-

quentIMasthex-rayattenuation increases, thex-ray
doseincidentonthedetectordecreases, resulting inhigheruncertaintyvaluesanddecreasedfiducialrecog-

toevaiuatetheseverityofartifacts24-26; thus,evaluationofmetalartifactusingothermetricshouldaIsobe
considered･FinallyitheROI thresholdingmethodmay
haveartificiallyloweredthemeasuredSDbyeliminatinginducedstreakartifacts.InthisstudXweusedthe
ROI thresholdingmethodbecauseoftheslightvariation insizeof the implantedball-shapedmarkers.
Nevertheiess, fbroptimal evaluation,artifactsshould
beassessedatconsistentdistancefromtheexpectedmarkerposition.

.n･aXFX4(Shimadzu,Kyoto,Japan)andVISICOIL(Seti
Medical, 1bkyo, Japan).Theirresultsshowedasimilartrendtoourresults･HoweveEtheyreportedthat intheliverregion,whenthewaterequivalentthicknessis
greaterthan25cm,fiducialmarkersaremoredifficult

torecognize,andtheprobabilityofsuccessfultracking
decreases230urresultsshowedthatevenwhenthe

waterequivalentthicknesswasincreasedto9､55,24.42
and31.34cm,somegoodrecognitionwasmaintained
mrGA0.28×20mmandGAO､4×20mmpartic-

ularlyUndertheconditionthateachfiduciaimarker

fiducialmarkers:GAO.28×10,GA0．28×20mm,GA
0.40mm×10mm,GAO､40mm×20mm,andACCU-

LOC(0.90mm×3mm)Wedemonstratedthepotential
toreducemetalartifactintheCTimagetothesamelevel
fbrall themarkersweevaluatedbyapplyingSEMAR.
AdditionallXthefiducialrecognitionofeachmarkermay

varydependingonthethicknessofthepatient'sbody
ParticularlMweshowedthatGA0.40×20mmmayhave
moreoptimal recognitionfbrCyberKniietreatment incasesofhighbodilythicknessincomparisontotheothermarkersevaluated･Theresultsofthisstudysupportthe
selectionoffiducialmarkersfOrCyberKnifetreatment.

O,28×10mmhadanuncertaintyofapproximately40%
undertheconditionof20cmTWthickness,resultingin
Iowerfiducial recognition.TherefOre,werecommenda
GAO､4mm×20mmtobeusedwhenthepatienthas
higherbodythicknessandthemarkeroverlapswiththe

Conceptualization:H､N,M.S.,andH.O｡DataCuration:
H､N,~I:S, ~I:S､,andKU.FormaIAnalysis:H､N,M.S,TTS.,
andZ｡MMethodology;H.N,M.S,T:S.,andH.O.P｢qectvertebralboneintheTLS.

Administration:HN,MS,H.~[,andH､0.Resources:H､N,

Thisstudyhadseveral limitations.Fir:,becausetheevaluationwasperfOrmedusingaphantom,CTartifacts,
andnduciairecognitionmaydifferdependingonthedif

H.N,MS.,and-IHS.Supervision:MS,H.TH, andH､0.
Writing-originaldraftpreparation:H.N,MS,TS.,and

AUTHORCONTRIBUTIONS

N､S,Z.M,K.M,rK,K.M,S.A,M.O.,andH､O.So廿ware:

匡陸塵く夢巨二命辰酢舅壺帷こぐ暉害展ｃｃとＥ堀Ｆ壱七二塁一口菌ｒ二に色こぐ⑤ｒｃ屋昌ご畠咋ｒ弓昌一

theconditionof20cmTWthickness.inaddition,GA

ThisstudyevaluatedtheCTartifactandfiduciairecognitionof fivefiducialmarkers includingnovel sizedｒ』ｃ『目と』ｃローこ』

overlappedthevertebralphantom,GAO.40×20mm,
andGAO.28×20mmhadsignificantlybetterfiducial
recognitionthanACCULOC(0.90mm×3mm)underall
conditions(liveimageacquisitionsettingandTWphantomthicknessevaluatedinthisstudy).ParticularIMGA
O,40×20mmhadthebestfiducial recognitionunder

5 ICONCLUSION

届僅邑ｃｒｃ三色産声霊藍妬涯桿℃脾拍・・…．。“也裳Ｃ三二茸弓室一三侭瞠冶ｃ一吾ｉｏｑｑ１１暉侶ＦⅡＡ豊目置呂昌昌７・匡茜莞旨吟】〆口斡

nition.Specincallyl increaseduncertaintyvaluewas
observedinpatientswithgreaterbodythickness,low
tubevoltageinDRRimaging,andenhanceddensityofhigh-absorbinganatomicalstructures,suchasthepelvis
andvertebral bones,whichoverlapfiducialmarkers.
TheiefOre,thisstudyevaluatedthefiducial recognition
ofclinicallyavailableandnovelsizenducialmarkers,andthe impactofdifferences inbodythicknessonnducialrecognition.
FOreachfiducialmarkeRfiducial recognitioninTLS
decreasedwithincreasingTWthickness.Yasueetal
evaluatedthefiducialmarkerrecognitionusingSync-

mayhave ledtodifferent resultsfromthoseof thepresentstudMInthefuture,evaluationoftheeffectson

ここ碓呉回皇君卜。一Ｊ』４卜皀冨ｒｃ昌糧目浸危も密画ｇ雷。要呂堀叱宍Ｌ邑弓糧侭ｒ』目園昌浬Ｃ邑｛ＥＣ、ご署卜と卜し』“しForfiducial recognitioninTLS,Marsicoetal. pera
fOrmedasubiectivevisualevaluationofCTimages,22
andourpreviousstudyevaluatedfiducial recognition

甲ferencebetweentheshapeofthephantomusedandtheactualpatient'sbodyshapeandphysiologicalbody
movements,suchasbreathing･Second,theshapeandorientationoftheimplantedmarkermaydifferdepend-にｃ更】ＥＣｇＥａ仁裳ｃ営一宮量目ｒ『＆僅回戸旨‐己再．目》、学笘肩￥向ｃ冨旨侯ｃshouldbeevaluatedunderotherconditions,andtheirimpactontheaccuiacyofcontouringthetargetandits

JOURNALOFAPPLIEDCLINICAL

レト。

NEMOTDETALNEMOTOETAL

1i2ili_LMEDICALPHYSICS
H.0.Writing-review&editing:H.N,M・S,TS.,andH.O
Thedatathatsupportthenndingsof thisstudyare
openlyavailableinMendeleyDataathttps:"doi.org/10.
17632/c9vrmr9ms3.1.
ACKNOWLEDGMENTS

CONFLICTOFINTERESTSTATEMENT
Theauthorsdeclarenoconflictsofinterest.
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