Vertebral compression fracture during stereotactic body radiotherapy for spinal metastasis: A rare case of tracking failure

Cancer/Radiothérapie24(2020)866–869

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Case

report

Vertebral

compression

fracture

during

stereotactic

body

radiotherapy

for

spinal

metastasis:

A

rare

case

of

tracking

failure

夽

Fracture

vertébrale

en

cours

de

radiothérapie

stéréotaxique

pour

une

métastase

vertébrale

:

un

cas

rare

d’échec

de

tracking

S.

Godin

,

A.-D.

Durham

,

L.

Schiappacasse

,

E.-M.

Ozsahin

,

F.

Vilotte

Departmentofradiationoncology,centrehospitalieruniversitaireVaudois,Bugnon46,CH-1011Lausanne,Switzerland

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received16January2020

Receivedinrevisedform7March2020 Accepted27March2020 Keywords: SBRT Tracking Spinalmetastasis Cyberknife Vertebralfracture

a

b

s

t

r

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Spinalmetastasisareadailychallengeinclinicalpractice.Stereotacticbodyradiotherapy(SBRT)allows deliveryofdefinitivetreatmentwithexcellentlong-termcontrolrates.Itsimplementationneeds ded-icateddevicesandday-to-dayimage-guidedradiotherapy(IGRT).TheXSightTM_{spinetrackingsystem,}

integrateswiththeCyberKnife®_(AccurayTM_{),providesafiducial-freetrackingsystemforspinalSBRT.We}

reportararecaseoftrackingfailureduringtreatmentduetotheoccurrenceofavertebralcompression fracture(VCF).

©2020Soci ´et ´efranc¸aisederadioth ´erapieoncologique(SFRO).PublishedbyElsevierMassonSAS.All rightsreserved. Motsclés: SBRT «Tracking» Métastasevertébrale Cyberknife Fracturevertébrale

r

é

s

u

m

é

Lesmétastasesvertébralessontundéfiquotidienenpratiqueclinique.Laradiothérapiestéréotaxique (SBRT)permetdedélivreruntraitementàviséeablativeavecd’excellentstauxdecontrôleàlongterme. Sonimplémentationnécessitedesappareilsdédiésetuneimageriederepositionnement(IGRT) quo-tidienne.Le«XSightTM_{spinetrackingsystem»,intégréavecleCyberKnife}® _(AccurayTM_),permetun

«tracking»sansrepèrefiducielpourlaradiothérapiestéréotaxiquevertébrale.Nousrapportonsiciuncas rared’échecde«tracking»encoursdetraitementdûàl’apparitiond’unefracture-tassementvertébrale. ©2020Soci ´et ´efranc¸aisederadioth ´erapieoncologique(SFRO).Publi ´eparElsevierMassonSAS.Tous droitsr ´eserv ´es.

1. Introduction

Approximatelyonethirdofallcancerpatientswilldevelopbone metastasis ofwhich approximately70% willpresent metastasis involvingthe vertebralcolumn [1–3]. Radiationtherapy canbe usedtomanagepainandtopreserveorrestoreneurologicdamages

[2,4,5].

夽 Acaseoffracture-relatedtrackingfailureduringspinalSBRT,S.Godin. ∗ Correspondingauthor.

E-mailaddress:Esat-Mahmut.Ozsahin@chuv.ch(E.-M.Ozsahin).

Ascancerpatientsexperiencelongersurvivalthroughimproved systemictreatmentsandasthereisaplaceforcurativeintentin oligometasticoroligoprogressivediseases,theaimoftreatmentof spinalmetastasisforthesepatientsisalsotoachievetumorcontrol

[2,3,6,7].

Inthis context,stereotacticbody radiotherapy(SBRT)allows highdosesandthereforeincreasedtumorcontrolwhilelimiting thedosetotheorgansatrisk(i.e.,spinalcord)throughastrong dosegradientandhypofractionation[1,3–6,8,9].

It requires dedicated radiotherapy systems, immobilization devices, and adapted image-guided radiotherapy (IGRT) [1,10]. AmongthedevicesforperformingspinalSBRTwiththese charac-teristics,theCyberknife®’sXsightTM_{SpineTrackingsystem}

(Accu-https://doi.org/10.1016/j.canrad.2020.03.016

S.Godinetal. Cancer/Radiothérapie24(2020)866–869

Fig.1. XSightspinetrackingsystem,showingmisalignmentbetweentheorthogonaldigitallyreconstructedradiography(DRR)andtheimage-of-the-daygrids.

ray,Sunnyvale,California)allowsfiducial-free(non-invasive),safe andeffectivespinetracking[4–6,8,9,11].

We hereexposeaninterestingcaseoftrackingfailureofthe Cyberknife®duringavertebralSBRT.

2. Casereport

Wereportthecaseofa65-year-oldmantreatedforaninitial stageIVAlungadenocarcinoma,withasinglebrainmetastasisat diagnosis.Treatmentconsistedofbrainradiosurgery,neoadjuvant chemotherapy (cisplatine-pemetrexed)followedby surgeryand adjuvantthoracicradiochemotherapy.

Threemonthsaftertreatmentcompletion,asinglelyticspinal metastasisonvertebraC3wasfoundonfollow-upexams,with cor-pusandleftpedicleinvasion.Nocollapsewashighlighted,andpain wasefficientlymanagedbymedication.Aftertumorboard evalu-ation, thislesionwasconsideredstablewitha spinalinstability neoplasticscore(SINS)of8,andanSBRTtreatmentbyCyberknife® wasdecided[12].

Planificationconsistedofamillimetricscanographicacquisition witha3-pointthermoplasticmask,registeredwitha3Dspine mag-neticresonanceimaging(MRI)forvolumedelineation.Prescription wasforatotaldoseof30/35Gyin5fractionswithsimultaneous

integratedboost(SIB)onthegrosstumorvolume(GTV).Clinical targetvolume(CTV)wasdefinedfollowinginternationalguidelines

[3,13,14].Themaximaldoseonavolumeof0.035cm3_(Dmax)tothe

spinalcordwas20.32Gy,theV20ofthespinalcordwas0.06cm3_.

TrackingwasassuredbytheXSightTM_{spinetrackingsystem,and}

eachfractionwassupposedtolast45minutes.

Thefirstfractiontookplaceasplanned,butduetosevereneck painintreatmentposition,painmedicationwasadjusted.The sec-ondfractionneededtobepushedbacktwicedue toneckpain andtheinabilitytocorrectlytrackthevertebra.Painwasinitially attributedtoa flareupeffectandmanagedbypainmedication adaptation.Trackingdifficultieswereimputedtoprojectionofthe mandibleonthetrackinggrid,andthemodificationinspine cur-vaturewasimputedtopain(Fig.1).Finally,onthethirdattempt, thesecondfractionwascompletedbutrecurrenttracking difficul-tiesdoubledtheexpectedtreatmenttime.Thedeliveryofthethird fractionwasalsoverydifficultbecauseofpainandtracking diffi-culties.Duetothesedifficulties,these3fractionsweredeliveredin 11days,insteadof5daysasusuallyinourdepartment.

Thesedifficultiesledustoreplanthetreatment.Onthesecond planningcomputertomography(CT)scan,aC3compression frac-turewasfound,withanear5-mmcorpusheightlosscomparedto initialimagery(Fig.2).Revisionofdailyorthogonalimageswith aradiologist showedthatthespinal fractureoccurredprobably

Fig.2.PlanningCT-scanbefore(A)andafter(B)C3vertebralcompressionfracture.

S.Godinetal. Cancer/Radiothérapie24(2020)866–869 betweenthefirstandsecondfractions,explainingtheincreased

pain and tracking difficultiesdescribed above.The recalculated doseonthesecondCT-scan(onwhichtheC3compressionfracture wasdiagnosed)showedadefavorablesituationwithanincreased dose to the spinal cord compared to the initial plan, with an estimatedDmaxof27.63Gy,aV20andaV22.5of0.53cm3_and

0.27cm3 _{respectively, for thecomplete plan. Moreover,further}

treatmentwiththeinitialplan wasnotpossiblebecauseofthe trackingdifficultiesand,moreimportantly,stabilizationoftheC3 vertebrawasnecessary,fortunatelystillwithoutneurologic symp-toms.

Afteranewtumorboarddiscussion,a kyphoplastywas per-formed,3weeksaftertheCT-scanonwhichtheC3compression fracturewasdiagnosed,withagoodantalgiceffect,andanewSBRT treatmentwasdecidedtocompletethetreatment.Two comple-mentaryfractionsweredelivered16 daysafterthekyphoplasty but,inviewoftheproblemsencounteredduringthefirstphaseof thetreatment(vertebralcompressionfracture,trackingdifficulties, uncertainties concerningthetimingofthecompressionfracture andthespinalcorddose),wedecidedtoreducethefractiondoseto 5/5.85Gytopreventtheriskofneurologiccomplications.The com-positedosimetryofthe2SBRTtreatments(3fractionsofthefirst planand2ofthisnewplanpostkyphoplasty)showedaDmaxof 22.32Gy,aV20andaV22.5of0.11cm3_and0.029cm3_{respectively.}

Nodifficultywasencounteredforthisnewtreatment.

The patient unfortunately died 3 months later due to rapid progressionofthedisease,particularlyintheformofpleural carci-nomatosis.

3. Discussion

Toourknowledge,thereisnocasedescribedintheliteratureof vertebraltrackingfailurebyCyberknife®duringaspineSBRTdue toanatomicalmodificationduringtreatment.Wewantedtoexpose thisexampleoftrackingfailureandalsotoreviewthedifferent pit-fallsinthemanagementofvertebralmetastasisbySBRT,especially usingtheXsightTM_{spinetrackingsystem.}

Spinal stability isa keyfactor inthedecision totreat verte-bralmetastasis.Vertebralinstabilityinthecontextofmetastasis isnotclearlydefined,andtheSpineOncologyStudyGroup(SOSG) proposedtheSINSscoretoprovideasimpleandobjectivesystem forassessingrelativestabilityofametastaticvertebra,whichthus allowstorecognize,intheabsenceofneurologicalsigns,unstable orpotentiallyunstablesituations.TheSINSscoreslesionsonascale from0–18usingsixvariables–pain,location,bonelesionquality (lytic/blastic),alignment,vertebralbodycollapse,and posterolat-eral element involvement.Lesions are then described as stable (0–6),potentiallyunstable(7–12),orunstable(13–18)[12].This scoreshowsagreatintra-andinter-observerreliabilityandis sim-pletouseforanyphysician,withincreasedreliabilitywithtraining

[15].Nevertheless,thisscorehasneverbeenevaluated prospec-tively,andisanexpertconsensus.Moreover,optimalmanagement oftheintermediatecategoryisnotclearlydefined.Theattitudeof spinalsurgeonsinthisintermediatecategorywasanalyzed retro-spectivelytodetectapossiblecut-offfromwhichanintervention isperformed,anditwasnotedthatonly11%ofSINS<10benefited fromsurgicalinterventionagainstalmost80%ofSINS>10.The pre-dominantSINSfactorsleadingtoaninterventionarealyticbone lesion,thelossofvertebralbodyheight,andtheinvolvementof theposterolateralelementsofthevertebra[10].Inoursituation, theSINScalculatedatourtumorboardwas8(potentially unsta-ble),withoutlossofheightofthevertebralbody.Nevertheless,itis possiblethatthisscorewasinitiallyunderestimated,inparticular byunderestimatingthepatient’spain(themostsubjectivevariable oftheSINS[16]),andthepatientdidnotbenefitfromaconsultation

withasurgeon,asrecommendedforpatientsintheintermediate category[12].

Afterstandardexternalbeamradiotherapy(EBRT),theriskof vertebralcompressionfracture(VCF)isaround3%withalowrate oflocalcontrolwhereastheriskafterSBRTcanincreasetoalmost 40%butwithlocalcontrolrates>80%[17].TheriskofVCFafter asingle-fractionSBRTishighwithanimportantinfluenceofthe doseperfraction.Indeed,theVCFriskis39%foradose>24Gy,19% for20–23Gy,and10%for<19Gy.WithfractionatedSBRT,therisk offractureis<5%(closetotheEBRTrisk),whilekeeping agood localcontrolof>80%[18].Single-dosespinalSBRTshould there-forebeusedwithcaution,giventhehighriskofcomplications.In additiontothedoseperfraction,otherpredictorfactorsofVCF afterSBRThavebeenidentified,includingsomecriteriausedin theSINS:alytictumor,pre-existingvertebralfracture,andcolumn deformity[19].Moreover,othercharacteristicswereidentifiedas predictorsinsomestudiesonly,suchassomehistologies(lungand hepatocellularcarcinoma),age>55years,locationfromthoracic10 vertebratothesacrum,majorinvasionofthevertebralbodybythe lesion(especiallyiflytic),andahighpainscore[16,20].Meantime betweenspinalSBRTandVCFisabout3months,and65%ofVCF occurwithinthefirst4months,eventhoughitcanhappenmore than1yearafter[1].Inourcase,we chosea fractionatedSBRT with5fractionsof6/7Gyperfraction,andidentifiedthattheVCF occurredprobablybetweenthefirstandthesecondfractions.So,it seemsimprobablethatonlyonefractionofSBRTledtothisVCF.

TheXsightTM _{spine trackingsystemoftheCyberKnife}® _uses

X-rayimage-guidedtargeting,andaroboticallymanipulated light-weight linear accelerator totrack themetastatic vertebra. The X-raytargetingsystemrepeatedly(typicallyevery30–60seconds) acquires high-resolution digital images onto paired orthogonal amorphoussilica detectors during treatment.These imagesare registeredtodigitallyreconstructedradiographs(DRR)generated fromtheplanningCT-scan.DuringtheSBRTplanning,aregionof interest(ROI)isdefinedontheseDRRs,usuallyaroundthetarget. WithinthisROI,agridispositioned.Differencesintranslationaland rotationalaxesbetweentheX-rayimageandtheDRRbasedonthe nodesofthegridsurroundingbonystructuresaroundthetarget aremeasuredandusedtomaintainspatialprecision.Theprocess ofimageacquisition,processing,registration,andre-targetingis automatic,and quicklyrepeatedduringtreatment[5,11].Inour situation,thelocationofthetreatedvertebra(C3)was mislead-ingbecausethetrackingdifficultieswerefalselyattributedtothe projectionofthemandible,amobilebonestructure,whichwasin thetrackingfield,andwhichcanthereforeleadtodifficultiesfor tracking,insteadofsearchingforananatomicalchangeofC3.In addition,theorthogonalimagingperformedfortrackingisdifficult tointerpretclinically,anddidnotallowustodiagnosethevertebral fracture.

Sincethecaseofourpatientdescribedabove,ourmanagement ofvertebralSBRThaschanged.TheSINSiscalculatedforallpatients presentedatourvertebralmetastasistumorboard,inthepresence ofneurosurgeonsandinterventionalradiologists.We systemati-callyassesstheindicationofastabilizationbeforeeverySBRT,even withalowintermediateSINS.Moreover,wedoanew radiologi-calassessmentmuchfasterincaseofsymptommodificationsor trackingdifficultiesduringtreatment.

Inconclusion,themanagementofvertebralmetastasisshould bediscussedinamultidisciplinarysetting,andSINSshouldbe cal-culatedtoavoidanycomplicationbyapossiblecombinedapproach betweenneurosurgery, interventional radiology, and radiother-apy.Thismethodshouldbepreferredespeciallyinthecontextof treatmentwithcurativeintentwherehighdosesperfractionare delivered.Moreover,infrontofanyclinicalmodificationorany trackingdifficultywiththeXSightTM _{spinetrackingsystem,one}

mustnothesitatetoredoplanningdiagnosticimaginginorderto 868

S.Godinetal. Cancer/Radiothérapie24(2020)866–869 searchforanyevolutionintheanatomybetweenplanningCTand

thetreatment.

Contributionofauthors

S. Godin: conceptualization, methodology, investigationand writing.

F.Vilotte:conceptualization,methodology,investigation, writ-ingandsupervision.

E-M.Ozsahin:supervisionandvalidation. L.Schiappacasse:supervision.

A-D.Durham:supervision.

Disclosureofinterest

Theauthorsdeclarethattheyhavenocompetinginterest.

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