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Medical
Engineering
&
Physics
jou rn a l h o m e pa g e:w w w . e l s e v i e r . c o m / l o c a t e / m e d e n g p h y
Technical
note
X-rays
sensing
properties
of
MEH-PPV,
Alq
3
and
additive
components:
A
new
organic
dosimeter
as
a
candidate
for
minimizing
the
risk
of
accidents
of
patients
undergoing
radiation
oncology
T.
Schimitberger
a,
G.R.
Ferreira
a,
L.C.
Akcelrud
b,
M.F.
Saraiva
c,
R.F.
Bianchi
a,∗,1 aLaboratoryofPolymersandElectronicPropertiesofMaterials,UFOP,OuroPreto,MG,BrazilbLaboratoryofPolymersPauloScarpa,UFPR,Curitiba,PR,Brazil cRadiotherapyCenterofCristianoVarellaFoundation,Muriaé,MG,Brazil
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received21December2011 Receivedinrevisedform30July2012 Accepted7August2012 Keywords: Radiotherapy Polymer Organicdevice Organicelectronic Dosimeter Smartsensor
a
b
s
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Inthispaper, wereportourexperimentaldesigninsearchingasmartandeasy-to-readdosimeter usedtodetect6MVX-raysforimprovingpatientsafetyinradiationoncology.Thedevicewasbased onanorganicemissivesolutionsofpoly(2-methoxy-5(2-ethylhexyloxy)-p-phenylenevinylene)
(MEH-PPV),aluminum-tris-(8-hydroxyquinoline)(Alq3)andadditivecomponentswhichwerecharacterized
byUV–Visabsorption,photoluminescenceandCIEcolorcoordinatediagram.Theopticalpropertiesof MEH-PPV/Alq3solutionshavebeenexaminedasfunctionofradiationdoseovertherangeof0–100Gy.It
hasshownthatMEH-PPV/Alq3solutionsarespecificallysensitivetoX-rays,sincetheeffectofradiationon
thisorganicsystemisstronglycorrelatedwiththeefficientspectraloverlapbetweenAlq3emissionand
theabsorptionofdegradedMEH-PPV,whichaltersthecolorandphotoemissionofMEH-PPV/Alq3
mix-turesfromredtoyellow,andthentogreen.TherateofthischangeismoresensitivewhenMEH-PPV/Alq3
isirradiatedinthepresenceofbenzoylperoxidethanwheninthepresenceofhinderedphenolic stabi-lizers,respectively,anacceleratorandaninhibitortoactivateorinhibitfreeradicalformation.Thisgives risetooptimizetheresponsecurveofthedosimeter.Itisclearfromtheexperimentalresultsthatorganic emissivesemiconductorshavepotentialtobeusedasdedicatedandlow-costdosimeterstoprovidean independentcheckofbeamoutputofalinearacceleratorandthereforetogivepatientstheopportunity tohaveinformationonthedoseprescriptionorequipment-relatedproblemsafewminutesbeforebeing exposedtoradiation.
© 2012 IPEM. Published by Elsevier Ltd. All rights reserved.
1. Introduction
Thefatal radiationoverdose of cancerpatientsunder radia-tiontherapyhasbecomearecentfocusofprovocativeheadlines andconcernofhospitals,healthcareorganizations,professionals inradiationoncologyandinstitutionsforimprovingpatientsafety [1–3].ThisissuewasfollowedbyinvestigationsfromtheAmerican AssociationofPhysicistsinMedicineandAmericanSocietyof Radi-ationOncology,whichhavebeensummarizedinrecentarticle[4]. Inviewoftheseveralrecommendationspresentedinthispaper toavoid equipmentmalfunctions and humanmistakes, it now seemstobeanappropriatetimetoproposeinnovativesolutions
∗ Correspondingauthorat:UFOP,35400000OuroPreto,MG,Brazil. Tel.:+553135591742.
E-mailaddresses:[email protected],
[email protected](R.F.Bianchi).
1 Presently,heisaVisitingScientistatDepartmentofElectricalEngineeringand
ComputerSciences,UCBerkeley-USA.
forindicationofdoseradiationdeliveredtocancerpatientsshortly beforebeingexposedtoradiationtherapytreatment.Thiswaythey willhavetheassurancethattheprescribeddosefortheircancer treatmentwillbeadministeredcorrectly.Unfortunately,errorsare commoninradiationtherapyandtoestablishmedicalandhospital routinestopreventnegativeimpactsonthetreatmentofpatients withcancerareacurrentchallenge[4–7].Someofthedifficulties inestablishingnewroutinesareassociatedwiththecomplexity ofcancertreatmentsandalsototightercontroloftheoperating conditionsofhospitalequipmentpriortopatientexposureto radi-ation.Therefore,investmentsinnewtechnologiescanensuresafe and effectivetreatments tocancerpatientsnot only becauseit willinformthatequipmentsareworkingproperly,butalsothat suchinformation canbeobtainedanddeliveredtothepatients, andthusarenotputtingthematrisk.Accordingly,these invest-mentswillcontributetoensurethatcancerpatientswillbetreated withrespect,supportandsecurityinagreementwiththegeneral conclusionsofRef.[4].
Thispaperreportstheexperimentaldesignofapersonal real-timeradiationdetectorfor6MVX-raysforimprovingpatientsafety
1350-4533/$–seefrontmatter © 2012 IPEM. Published by Elsevier Ltd. All rights reserved.
in radiation oncology.Our main goal is tofind and evaluate a newsystemwithpotentialuseasaneasy-to-readdoseindicator radiationdetectorwhichshouldnecessarily beinexpensiveand thusaccessibleinplaceswithlimitedresources.Firstly,wewill considertheeffectofirradiationontheopticalpropertiesof light-emittingpolymers(LEPs)[8–12],whichcanbeeasilydetectedby irreversiblecolorvariation ofsuchorganicmaterialsduringthe irradiationprocess[12–15].Thesimplecorrelationbetweendose andcoloristhemainfeatureoftheproposeddevice.Infact,the phe-nomenonofcolorvariationinducedbyradiationnotonlyreveals theirreversiblechangesthatcanoccurontheopticalpropertiesof LEPsduringradiationtherapytreatments,butalsoprovidesa real-timeindependentverificationandconvenientprobeformonitoring radiation doses delivered by external beam radiation machine orequipment-relatedproblems,suchasradiationunderdoseand overdose.
2. Experimentalprocedures
Poly(2-methoxy-5(2-ethylhexyloxy)-p-phenylenevinylene) – MEH-PPVand[aluminum-tris-(8-hydroxyquinoline)]–Alq3were
purchasedfromAldrichSigmaanddissolvedinchloroformat a MEH-PPV/Alq3(w/w)ratio equalto0.5 asdescribed elsewhere [14,15].MEH-PPV/Alq3wasalsodissolvedinchloroform
contain-ingbenzoylperoxide(fromAldrichSigma)andhinderedphenolic stabilizers (Irganox 1010@, from Ciba Specialty Chemical
Cor-poration),an acceleratorand aninhibitor ofradicalformations, respectively.Theadditiveswereusedtoenhancethestabilityof MEH-PPVby ahinderedphenol aswelltoreduceit by peroxi-des [16,17], and nosignificant differences in the lineshape of ABSandPLcurvesofMEH-PPV/Alq3solutionswereobservedwith
thepresenceoftheseadditives.Thesesolutionswillbedescribed asMEH-PPV/Alq3:acceleratorandMEH-PPV/Alq3:inhibitor.Infact,
thesamples were prepared in thedark to avoid light-induced degradationof theorganicsystems, and molecularsieveswere addedtochloroformtoremovethetracesofwater.Althoughno systematic study of the effect of oxygen, moisture or daylight was undertaken, no visible change was noticed on the pris-tine samples that stood exposed to daylight on thelaboratory forseveraldays.Finally, thesolutions weretransferredtoglass ampouleswhich werethenflame-sealedtoavoid solvent evap-oration.Thespecificationsforampouleswere:nominalvolume, diameter,externalthicknessandwallthicknessof1.25ml,10mm, 8.0mmand0.50mm,respectively.Theirradiationofthesamples byX-rayswasperformedattheRadiotherapyCenterofFundac¸ão CristianoVarella–Braziltoevaluatetheeffectofionizingradiation intherangeof0–100GyontheopticalpropertiesofMEH-PPV/Alq3
hybridmaterial.In thepresentstudy,VarianClinac600CLINAC computer-controlledequipmentwithaconventionalX-rayssource wasused.Thismachinegeneratesa6MVX-raysbeamwith rectan-gularsymmetricfields[18]anddeliverstheexactprescribeddose tothepatientinthelowestnumberofmonitorunits.The irradi-ationofsampleswasperformedinawaterphantomaccordingto IAEATRS398dosimetryprotocols[19]atasource-surfacedistance of100cm witha(30cm×30cm)field in ordertosimulatethe standardconditionsofcancertreatment.Thephotoemission(PL) spectraofMEH-PPV/Alq3systemswasrecordedusinganUSB2000
OceanOpticsspectrophotometer,withanInGaNlaser(=405nm, 10mW)asexcitation source.Finally,UV–Visabsorptionspectra werecarriedoutinthe300–800nmrangeusingtheShimadzuUV 1650equipment,andthecolorcoordinatesofCIE(1931) chromatic-itydiagramwereobtainedusingthePLspectraoforganicsolutions andtheColorCalculator FreeSoftware.Allmeasurementswere doneatroomtemperature.
Fig.1. UV–Visabsorption(ABS)andphotoemission(PL)spectraobtainedfrom MEH-PPV,Alq3,andMEH-PPV/Alq3solutions.Allmeasurementswereperformed
atroomtemperature.ThePLspectrawererecordedontheUSB2000 spectropho-tometerwitha405nmlaserasexcitationsource.
3. Experimentalresults
TheopticalresponseofMEH-PPV,Alq3andMEH-PPV/Alq3
solu-tionsareshowninFig.1.Themainpeakswereobservedtooccur at495nmand385nmforabsorption(ABS), andat560nmand 515nmforphotoluminescence(PL)forMEH-PPVandAlq3,
respec-tively.AsinglePLpeakat560nmandtwodistinctabsorptionpeaks at385nmand492nmwereobservedforMEH-PPV/Alq3.This
fig-urerepresentsacontrolexperimentwhichdemonstratesthatboth MEH-PPVandAlq3absorptionspectraareobservedtooccurinthe
MEH-PPV/Alq3hybridmaterial,whilethePLofAlq3isreabsorbed
bytheMEH-PPV. Thisfindingindicatesthat anenergy transfer processfromAlq3toMEH-PPVistakingplace,sincealarge
spec-traloverlapbetweenAlq3 emissionand MEH-PPVabsorptionis
observed.Thisisinagreementwithreportedresults[20] describ-ingtheinfluenceofsmall-moleculematerialontheperformance ofMEH-PPV-basedsolarcellsindicating aprobability ofFörster energytransferfromAlq3toMEH-PPV.
3.1. Influenceof6MVdoselevelsontheopticalpropertiesof MEH-PPV/Alq3hybridmaterial
ItcanbeseenfromFig.1thatthereexistsared-orange emis-sionbandbetween520nmand 690nmfor both MEH-PPV and MEH-PPV/Alq3solutions.LetusassumetheFörsterenergy
trans-ferfromAlq3toMEH-PPVandalsotheinstabilitytoradiationof
substitutedpoly(phenylenevinylene)–PPV[21–23].Bearingthese pointsinmind,itseemstobereasonabletoexpectaquenching ofthePLintensityduetothedecreaseofthepolymerconjugation lengthunderexposuretoradiation[21,23,24],andthusaless effec-tivespectraloverlapbetweentheabsorptionofMEH-PPVandthe emissionofAlq3.
Thefindingsoutlinedabovehavebeenappliedtothedesign ofa novelsmart organicdetectorofX-rays (6MV) using MEH-PPV/Alq3-based material. We illustratethis by considering the
designofanX-raysdoseindicatorshowingcolorvariationfrom redtoyellow,andthen togreen whenexposedtodosesinthe rangeof0–100Gy.InFig.2isdisplayedtheeffectofradiationon boththeopticalproperties(ABSandPL)ofMEH-PPV/Alq3
solu-tion.It isobserved thattheMEH-PPV absorption(370–560nm) andred-orangeemission(520–690nm)bandsshifttowardslower wavelengthsanddecreaseinintensitywithdoselevels,whilethe Alq3absorption(300–450nm)andgreenemission(450–650nm)
bands remain constant with substantial increases in intensity, respectively. Aninset toFig.2 shows the linearity ofthe peak
Fig.2. UV–Visabsorption(ABS)andphotoemission(PL)spectraobtainedfrom MEH-PPV/Alq3solutionsexposureto6MVX-raysdosesequalto0,10,20,40,60,80
and100Gy.Allmeasurementswereperformedatroomtemperature.ThePLspectra wererecordedontheUSB2000spectrophotometerwitha405nmlaserasexcitation source.Inset:peakemissionwavelength(max)ofMEH-PPV/Alq3solutionsexposed
toX-raysdoses.
emissionwavelength(max)vs.doseofMEH-PPV/Alq3 solution.
Fromtheseexperimentalresults,itisshownthatablendofthetwo luminescentorganicmaterialsinsolutionthereforeundergoesa blue-shiftinPLemissionandabsorptionastheyareexposedto radi-ation,formingthebasisifalinear-responsedosimeterforradiation oncology.
3.2. Influenceof6MVdoselevels,benzoylperoxideandof hinderedphenolicstabilizersonperformanceof
MEH-PPV/Alq3-baseddetector
Figs. 3 and 4 show the radiation dose evaluation to MEH-PPV/Alq3:inhibitor,MEH-PPV/Alq3andMEH-PPV/Alq3:accelerator
solutions.Theirradiationusedwas6MVX-rays,andtheresults were obtained from direct measurement on the CIE (1931)
Fig.3.CIE(1931)chromaticitydiagramobtainedfromMEH-PPV/Alq3:inhibitor,
MEH-PPV/Alq3andMEH-PPV/Alq3:acceleratorsolutionsexposureto6MVX-rays
dosesequalto0,10,20,40,60,80and100Gy.Thediagramswereobtainedusing thePLspectrashowedinFig.2andtheRadiantImagingColorCalculatorFree Soft-ware.(Forinterpretationofthereferencestocolorinthisfigurelegend,thereader isreferredtothewebversionofthearticle.)
Fig.4. Setof7sealedglassampoulesfilledwith(a)MEH-PPV/Alq3:inhibitor,(b)
MEH-PPV/Alq3and(c)MEH-PPV/Alq3:acceleratorsolutionsobtainedfromexposure
to6MVX-raysdosesequalto0,10,20,40,60,80and100Gy.Alltheorganicmaterials wereexcitedbyavioletlight(emittedfromavioletLEDwithwavelengthfrom380 to410nm).(Forinterpretationofthereferencestocolorinthisfigurelegend,the readerisreferredtothewebversionofthearticle.)
chromaticitydiagramandonthepicturesofasetofsevenexcited organic samples exposed to 0, 10, 20, 40, 60, 80 and 100Gy. All samples were mounted in a specially constructed sample holderandexcitedwithavioletLED(380–410nm)atanoblique angle.Thedosimetersemissionchangedfromredtogreenwhen the dose rises above 40Gy for MEH-PPV/Alq3:accelerator, and
above60GyforMEH-PPV/Alq3andMEH-PPV/Alq3:inhibitor.With
further increases in doserate, Fig. 5 shows the peak emission wavelength (max) MEH-PPV/Alq3:inhibitor, MEH-PPV/Alq3 and
MEH-PPV/Alq3:acceleratorchangedlinearityfromgreento
green-ishbluewhendosereached60,80and100Gy,respectively.The coloroftheorganicsolutionsdoesnotchangebackafterexposure toradiation.Infact,asetof21samples,allthreeofthemwere irra-diatedwiththesamedose(0,10,20,40,60,80and100Gy)showed averysimilarcolor-changingresponse.Thisprocedureguaranteed reproducibilityinthepreparationprocesses,andalsothehigh opti-calperformanceoftheorganicsolutions.
ItcanbeseenfromFigs.3–5thatadditionofbenzoylperoxide (accelerator)hasenhanceddegradationprocessofMEH-PPV,while theaddition ofhindered phenolic stabilizers (inhibitor), onthe
Fig. 5. Peak emission wavelength (max) vs. dose obtained from
MEH-PPV/Alq3:inhibitorand MEH-PPV/Alq3:accelerator solutions exposedto X-rays
doses.
otherhand,hasretarded.Itisclearfromtheseexperimentaldata thatareasonably self-consistentpicturehasemerged regarding thebasicdegradationprocessofMEH-PPVenhancedbyhindered phenolicstabilizersandreducedbybenzoylperoxide.Ourfindings wouldseemtodemonstratethattheradiationexposurepromotes changesintheabsorptionandphotoluminescencespectraof PPV-typepolymersthatpointtowardstheideaofchainscissionand decreaseof conjugation length.Thiseffectis attributed to rad-icaltransfer reactionfrom thepolymer backbonetothe added compound,whereitisstabilizedbyresonanceintherings. Con-sequently,theslowdownofthephotodegradationbythepresence ofthefreeradicalscavengerindicatesthatfreeradicalsactasan acceleratorofthephoto-oxidationprocess.However,despitethis effort,there arestill uncertainties associatedwithrole ofthese compoundsonthedegradationprocessofPPV-typepolymers,thus becomingasignificantsubjectofstudyforfuturepublications[17]. 4. Conclusions
Inthispaper,wehavereportedtheresultsofaninvestigation ontheuseofasmallmolecule/light-emittingpolymerhybrid mate-rialtoproduceanewradiationdosimeterforminimizingtheriskof accidentsofpatientsundergoingradiationoncology.Device oper-atingprincipleisbasedonchangingtheeffectivespectraloverlap betweentheabsorptionofMEH-PPVandtheemissionofAlq3
solu-tionsduringirradiationprocess.Thisprinciplewaschosenfrom reasonsoftheinstabilitytoradiationofMEH-PPV,andthe possi-bilityofcontrollingthedegradationrateofthisPPV-typepolymer byaddingfreeradicalsscavengersordeliveringcompounds.The resultspresented demonstratedthatMEH-PPV/Alq3 devices can
successfullybeprogrammedtooperatefrom0to100Gy.Thebasic ideabehindthisconceptconsidersthesensorasanovelorganic luminescencetrafficlightdeviceinwhichredrepresents,for exam-ple,underdoseandgreentheprescribeddose,whileorange-yellow suggeststhatradiationtherapyprocedureisanongoingprocess
andgreenishblue,overdose.Oneofthebenefitsoftenpointedout inconnectionwithRef.[4]isthat theMEH-PPV/Alq3 dosimeter
hasthecapabilityof easilyprovidingtheradiationdoseshortly beforetheradiationtreatmentofcancerpatientstoavoidfatal over-doseorunderdose,becausethemajorityoftumorsrequiredoses intherangeof8–70Gy,whicharefractionedindosesof1.8–2.0Gy once a day, five times a week for 5–7 weeks. The conclusion tobedrawn fromall theworkin searching a smart and easy-to-readdosimeter isthat,although thesensitivity,performance andreproducibilityMEH-PPV/Alq3-baseddosimeterhavenotyet
beenexplored,theresultspresenteddemonstratethat:(i)small molecule-light/emittingpolymerhybridmaterialcansuccessfully appliedasadisposable,personalandverylow-cost(<US$1)X-rays detectorforminimizingerrorsintheapplicationofmedical radi-ation,suchasmiscalibrationofaLINACincomeunitresultingin incorrecttreatmentdose,andtogivepatientstheopportunityto haveinformationonthedosecalibration,equipment-related prob-lems andsystemfaults a fewminutes beforebeingexposedto radiation,and(ii)themonitoringofthisdevicemayalsobe eas-ilyachieved,forexample,byestablishingcalibrationconditionsfor colorsobtainedbypassingtheradiationthroughtheorganic sys-tem.Acheckagainstastandardizedcolorchartcaneasilysupply thedelivereddose.
Acknowledgments
This research was supported by the CNPq (grant num-bers 305646/2010-9 and PDE 200682/2011-3), by Rede Nanobiomed/Capes, by CNPq-Fapitec-SE/NExSEN, by Fapemig (grantnumbersPPM-00596-11,PPM-00306-09and APQ-04124-10)andbyINEO/CNPqAgenciesfromBrazil.RodrigoF.Bianchiwas alsosupportedbyCNPq(grantnumbers305646/2010-9andPDE 200682/2011-3)andbyFapemig(grantnumbersPPM-00596-11, PPM-00306-09andAPQ-04124-10).
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