Beta Particle Emitting Ophthalmic Applicators

1 Page 1 NBSMeasurementServices: Calibrationof Beta-Particle-Emitting OphthalmicApplicators U.S.DepartmentofCommerce NationalBureauofStandards Open at page → 2 Page 2 CenterforRadiationResearch TheCenterforRadiationResearchisamajorcomponentoftheNationalMeasurementLaboratory intheNational BureauofStandards. TheCenterprovidestheNationwithstandardsandmeasurementservicesforionizing radiat... Open at page → 3 Page 3 NBSMEASUREMENT SERVICES: CALIBRATIONOFBETA-PARTICLE- EMITTINGOPHTHALMICAPPLICATORS JohnS.Pruitt CenterforRadiationResearch NationalMeasurementLaboratory NationalBureauofStandards Gaithersburg,MD20899 U.S.DEPARTMENTOFCOMM... Open at page → 4 Page 4 LibraryofCongressCatalogCardNumber:87-619844 NationalBureauofStandardsSpecialPublication250-9 Natl.Bur.Stand.(U.S.),Spec.Publ.250-9,36pages(July1987) CODEN:XNBSAV Commercialproducts—materialsandinstruments—areidentifiedi... Open at page → 5 Page 5 PREFACE Thecalibration andrelatedmeasurement servicesoftheNationalBureau ofStandardsareintendedtoassistthemakersandusersofprecision measuringinstruments inachievingthehighestpossiblelevelsof accuracy,quality,andproductiv... Open at page → 6 Page 6 ABSTRACT Thisserviceprovidescalibrations for^^Sr+ betaparticle ophthalmicapplicators. Thecalibrationdeterminestheaverage surfaceabsorbed-dose ratetowaterovertheactiveareaofthe applicator. Thetechniqueusedistomeasurecurre... Open at page → 7 Page 7 CONTENTS Page Abstract iv ListofFigures v1 1.TheCalibrationService 1 2.TheGeneralApproach 2 3.Description oftheSystem 3 4.Operational Procedures , . . . 10 4.1Currentmeasurement andcorrection 10 4.2Measurement ofsourcear... Open at page → 8 Page 8 LISTOFFIGURES Page Fig.1.NBS-ownedophthalmicapplicator SN0258 1 Fig.2.Electronenergyspectrumfroma^^Sr+^^Ysource 2 Fig.3.Crosssectionof30-mmdiametercollectingelectrodeunit, showingrelativepositionofhighvoltageelectrodeand... Open at page → 9 Page 9 1.TheCalibrationService Thisserviceisintendedtoprovidecalibrations for^^Sr+ beta- particleapplicators usedinmedicinefortreatmentofophthalmicconditions. Itwasstartedin1977. Atypicalophthalmicapplicator isshowninfigure1. I... Open at page → 10 Page 10 Thisservicewascalled8.4KintheoldSP250manual. Thedesignation hasbeenchangedto47030Cinthe1986versionofSP250.1 Thelatteralso containsinstructions forshippingandhandlingtheapplicators. Areportentitled"Calibration ofBeta-Part... Open at page → 11 Page 11 Thedetermination ofaveragesurfaceabsorbed-dose rateisperformed in twostepsusingionizationchambersofdifferentdiameters,becausetwo quantitiesneedtobemeasured. Thetotalcurrentperunitairgapatthe sourcesurface,(I/d)^,ismeasur... Open at page → 12 Page 12 Theparticularcollectingelectrodeshownhasadiameterofabout30mm andissurrounded byaguardelectrodewithanoutsidediameterof50mm. Bothguardandcollectingelectrodes aremadeof8-mmthickA-150conducting plastic,electrically isolatedw... Open at page → 13 Page 13 5 Open at page → 14 Page 14 •Extrapolation chamber Fig.5:Sideviewofextrapolation chamber(above)andsourcesupport structure. NBSapplicator SN0258isshown. 6 Open at page → 15 Page 15 Formeasurements ofthesource areaA,thecollecting-electrode- guard-electrodeunitoffigure3can beliftedoutoftheextrapolation chamberandreplacedbyaunitwith approximately thesameoutlinebut withamuchsmallercollectingelec- trode... Open at page → 16 Page 16 Duringmeasurements ofboth(I/d)^andA,thesourcesurfacemustbe raiseduntilittouchestheextrapolation chamberhigh-voltage-electrode foil. (Thisdoesnotproduceashortcircuitsinceonlytheinnerfoilsurfaceisat highvoltage.) Fordeterm... Open at page → 17 Page 17 Et_ OO) i-(-> 4—O) O)o 00t_ •r-4-> 3:O ^OJ o.— o<u on •> -t-> c:^ O)=» eo Z3— • £_ C_ -!->t- (1) 00OJ4_> c -(->o; •r-a;e Eo C7>+->L_ •r-O t_> =3 -a V) IT- fCfOo <D-Mt- E-r-OJ CDC fT3^ .—-C\J 4_)— ' -c -a •r—t_ (tJ c_O) —... Open at page → 18 Page 18 constantforceontheflexiblehighvoltageelectrode. Ithasbeenfoundthat electrodeflexureisnegligible ifthevoltagegradientdoesnotexceed 40V/mm.Measurements havebeenmadesuccessfully withgradientsbetween 10V/mmand40V/mm.Correcti... Open at page → 19 Page 19 Themeasuredcurrentisthesumoftwocomponents, anioncurrent generated inthechamberairgapbyinteractionbetweenairmoleculesandthe incidentbeta-particles, andaparasiticcurrentgenerated inthebodyofthe collectingelectrodebybeta-pa... Open at page → 20 Page 20 Thegraphofparasiticcurrentinfigure8showsevidencebothof electronscomingtorestinthecollectingelectrode(thecentralpeakofthe distribution), andbackground (thenegativetails). Thecentralpeakofthe parasiticcurrentismoresymmetri... Open at page → 21 Page 21 WiththeapplicatorandHV-electrode foiljustbarelyseparatedbyeye,the operatorcanmeasuretheion-chambercurrent,reducetheseparation by0.01mm usingthebarrelmicrometerreading,repeatthecurrentmeasurement, etc. It willbefoundthatt... Open at page → 22 Page 22 IfXqandyarethevaluesofxandywiththeapplicatorcenteredby 0 eyerelativetothecollectingelectrode, ithasbeenfoundthat36current measurements at'2-mmintervalsovertherangesXq-5<x<xq"*"^ yQ-5<y<Yq+Scoveralargeenoughareasothatthec... Open at page → 23 Page 23 dm (8) whereintermsofthecoordinates offigure1,y =r/R,n =Az/R, r=/x2+y2,andKisaconstant. Thisequationwasderivedbytheauthorassumingthattheactivityis spreaduniformlyoveracircleofradiusRonthesourcesurface,thatthe beta-partic... Open at page → 24 Page 24 SN0258 THEORY Figure11isaplotofprobeioncurrent vs^.radiusfortwoapplicators and matchingsourceprofilescalculatedfromeq(8).Theparameterazwas assignedtheapproximatevalue0.1mminthecalculation, andvaluesof R=3.18mmand4.35mmwe... Open at page → 25 Page 25 Fig.12:Frontviewofextrapolation chamber(above),showingsourcesupport structureretractedforqualityassurancemeasurements. NBS applicatorSN0258isshownwithitsplasticshieldmovedtowardsthe source. 17 Open at page → 26 Page 26 Way =exp(XAt) (9) whereAtisthetimesincethereferencedateof1986Jan1,andxisthe decayconstant(6.659 x10" ^dayifor90sr). Finally,Qqshouldbedetermined byfittingthecorrectedcurrentstothe equation: I=Cq+c^g (10) andcalculating:... Open at page → 27 Page 27 Thecorrectedcurrentperunitairgapatzeroairgap,(I/d)g,comes fromfittingthefivecorrectedcurrentstotheequation: I/d= (I/d)o(1+ad+ 6d2) (12) Thisextrapolation isonlyapproximate forthispoor-geometry determination. Sometimes aq... Open at page → 28 Page 28 6.CalibrationUncertainty Thereissomeuncertaintyassociatedwitheachtermofeq(13).Those determined byextrapolation-chamber measurements withthe30-mm-diameter collectingelectrode, suchas(I/d)Qandk^Q^--| ,have(relative)standar... Open at page → 29 Page 29 REFERENCES 1.Calibrations andRelatedServices,NationalBureauofStandards, Spec.Publ.250,Gaithersbury ,MD20899(1986). 2.J.S.Pruitt,"Calibration ofBeta-Particle OphthalmicApplicators at NBS,"J.Res.Nat.Bur.Stand.(U.S.),91,165... Open at page → 31 Page 31 APPENDIXA.Examplesfromadatabook TheexamplesgivenarefourpagesfromdatabookDB863,pages133-136. Thesecoverthecalibrations ofapplicatorSN176. Thefirstthreepagescover theareadetermination, usingprobeelectrode0.5A,andthefourthp... Open at page → 32 Page 32 z,d: Sourcedistanceandelectrodeseparation, respectively, bothinmm. A,9(org,e): Theextrapolation chambercoordinatesneededtoobtaintheelectrode separation d. i(org)ismeasuredintenthsofaninchand6in fractionsofarevolution. m,... Open at page → 33 Page 33 NBSS06—Analyalfpap«r 901-10? GPO 9«70F—•404e« U/»A^/n - /I /) 1 IA -ir/jo g>-. <^.a SN 17^^ . ( •37«7 bTi 677^ — -T7<?4 ^i77^— -;37 ' 177 iTHI'o.HW €,Oo •f 32/ — I7i - 377— - - Ho - 7^/ 7f ._r3„ - -^•^-^ 7< 7/ 2_'^5_ 17... Open at page → 34 Page 34 13^ NBS506—Analytlipaper 901-10? croi»i2of ^1 J) *J 1/\/ vnHv ^ .-^T^h .^ /^H^0,1 l|«,2.3V ' - -1-77 - - - 1 5",75" 4. 7 1 -— - 1A35 HI ^,L0 -t- <J27 - 1 1 - 2)1,0 Oil 11^5',C'5+ _ s:c7 4- /I - — . -7.066- £'.11 f "l/t'... Open at page → 35 Page 35 NBS306—Analysispap«r GPOt»«2or—•«048« lijWW] A-5 Open at page → 36 Page 36 NHS.'>06—Analyiltpaper 901-10 • CPO 19«2OF—*404*« r/ n r S- 4.^H l=^== L ^ )l A 1 ^/^p J/ J + i\7 &n ... .._ ici^l.lpF o -> , .... •f — - JAO -14;^ ^— _ •J^c^„ ACA .— — . ^fj 1 _ »- —-- LC^ 7.7c^Z^' - . . 1 t -fjor ^.1^7... Open at page → 37 Page 37 APPENDIX B OG8420/86 OB863/133 TFN?35324 1985JUN24 Pdge Iof2 IJ.S.DEPARTMENT OFCOMMERCE NATIONALBUREAUOFSTANDARDS GAITHERSBURG. MO20899 REPORTOFCALIBRATION ^^SrBeta-particle Source Submittedby TechnicalOperationsSourceNo... Open at page → 38 Page 38 OG84^0/85 1985JUN24 Pdtjp?of^ Forthesourcesubmitted, onecalibration wasmade,todeterminetheaverage absorbed-dose ratetowateracrossthesurfaceofthesource. Theactive sourceareawasdeterminedbymappingtherelativedoserateacrosst... Open at page → 39 Page 39 FORMNBS-114A(REV.1184) U.S.DEPT.OFCOMM. BIBLIOGRAPHICDATA SHEET(Seeinstructions) 1.PUBLICATIONOR REPORTNO. NBS/SP-250/9 2.PerformingOrgan.ReportNo 3.PublicationDate July1987 4.TITLEANDSUBTITLE InBSMeasurementServices: Ca... Open at page → 43 Page 43 PUBLICATIONS INTHESP250SERIESFROMTHECENTERFORRADIATIONRESEARCH SP250-1 NBSMeasurement Services: SpectralRadianceCalibrations J.H.Walker,R.D.Saunders, andA.T.Hattenburg SP250-2 NBSMeasurement Services: FarUltravioletDetec... Open at page → 44 Page 44 U.S.DepartmentofCommerce NationalBureauofStandards Gaithersburg,MD20899 OfficialBusiness PenaltyforPrivateUse$300 Open at page →