Koshida Kichiro

Takayama Teruhiko

Kanazawa University Repository for Academic Resources

IVmMOIRSALl凪ｎＰＲＯＥＫＡＮＡＺＡＷＡＶｏＬ１８２３～2８１９９４OriginalArticleEffectsoftheMirlDrPositionontheDistributionofX-raylntensityinRadiatio、FieldKichiroKoshida，TeruhikoTakayamaABSTRACTWeevaluatedtheeffectsofmirrorpositiononthedistlibutionofX-rayinten‐sitywithintheradiationfieldlntｈｅdirectionparalleltothetubeaxls，exposureatthepositiontowardtheanodedecreasedremarkablyWithincrcasingdistancefromthecenter､Ｏｎｔｈｅｏｔｈｅｒｈａｎｄ,inthedirectiOnpelpendiculartothetubeaxis，theeffectofdistancefromthecenterwasnotsoprominent、AtthepositionsintheparaUelorperpendiculardirection,homogeneousintensityareashiftedtowardthecathodeortheposterior,respectively、ThemaxlmumdiffermceofX-rayinte､‐sityatthedifferentmirrorpositionｗａｓ12.0％、Wheneverwetakearadiography，wealwaysshouldconsiderthepositionofthemilrorinthebeamlimitingdevicetogethomogeneousX-rayintensitywithintheradiationfieldWhenthemirrorisplacedat(A)positionwher℃ｔｈｅａｎｏｄｅｓｉｄｅｏｆｔｈｅｍｉｎ｢orapproachestheanode，theimprovementcanbeexpectedshowingunifOｒｍｉｔｙＯｆ12%←●ＫＥＹＷＯＲＤＳMirrorpOsition,X-rayintensity,Aluminumequivalent,EXposure,TaigetＩＮＴＲＯＤＵＣＴＩＯＮＩｔｉｓｗｅｌｌｋｎｏｗｎｔｈａｔX-rayintensityisnothomogeneousoverthewholeradiationfieldHowever，inordertogetexcellentradio‐grams,X-rayintensityshouldbekeptasｈｏｍｏ‐geneousaspossibleOfvanousfactorssuchastargetangle,anodematerial，filtration，mirror,ａｎｄｓｏｏｎ,thepositionofamirrorplayStheimportantrole，ｂｅcausebeamlimitingdeviceiseasilytumedtoseveralpositionsaccordingtokindsofradiographyandposi‐tioningofpatients，amirroreqUiPpedinthebeamlimitingdevicealsochangestlleposi‐tionrelativetotheX-raytubejTheeffectofmirrorpositionsonthedistributionofXTayintensitycan，tbeignoredinthelargeradia‐tionfield，althoughitmaybenegligibleinthesmallfieldSomeauthors1-3)reportedtheangu‐lardistributionofX-rayintensityondiagnos‐ticX-raytubes,However,theeffectsofmirrorpositionsonX-rayintensityhavenotbeenreporｔｅｄＴｈｅｐＵｒｐｏｓｅｏｆｔｈｉｓｐａｐｅｒｉｓｔｏｅｖaluatetheeffectsofmilrorpositionsonthedistribu‐tionofX-rayintenSitywithintheradiationfield，andtodecidethemostappropriatepositiontogethomogeneousX-rayintensity．１．MAT1DRUAmRAsix-peakhigh-voltageX-raygeneratorwasused・ＡｎＸ－ｒａｙｔｕｂｅ(CIRCLEXq8P38CS,Shi‐madzuCorp.）hasthefO11owingdimensions；0.8ｘＯ８ｍｍＯｆｆｏｃｕｓｓｉｚｅ，１２degreesoftargetangle,andinherentfiltrationequivalentL5mmaluminUm(Ａ１).Thebeamlimitingdevice(TypeR-20）ｉｓｅｑＵｉｖａｌｅｎｔｔｏＡｌｏｆＬＯｍｍｉｎｔｈｉｃｋ‐DepartmentofRadiologicalTechnology,SChoolofAlliedMedicalProfessions,KanazawaUniversity－２３－ＫＫｏＷａｔｚ,ｅＺａＬT隼 ｅｔｒｒｏｒ (CME）(A） (D）(B）ジンａｍｐｕｓｔａｂ１ｃＤｉａｐｈｒａ８ｍ Tｊ Tｊ正10 Ｃ、Ｉ特Ａ一Ｆ＝てｇｉ＋-21.3 121Jｃ、0.0３０`c□ :薑｣＝>(（ ）））Ｉｍａ８ｉｎｇ ＴａｂｌｅＦｉｇ、lGeometHyinthisgtudy．Ｂ,Beamlimitingdevice.；Ｉ,IONEXionizationchamber・ThetaIget-toch2mherdistanceislOOcmandthechamber-to-tabledistzunceis３０ｃｍ・Theradi2tionfieldis35cmx42.5cｍ（l4inchxl7inCh）ｉｎｓｉｚｅ．Arrang巴ｍｅＩｕｔｏｆｔｈｅｍｉｒｍｒｒｅ１ａｔｉｖｅｔｏｔheX-raytmbe．Ａ,Anode.;Ｃ,Cathode.；TjTarget.；Ｍ,MiITor.(A),Therightendofthemirrorapproachestothetube；(B)ａｎｄ(D),TheposteriorendofthemilTorapproaChestothetuba;(C)ａｎｄ(E),Theleftendofthemilmrapproachestothetube.（A),⑱)，ａｎｄ（C）ｓｈｏｗmeasurementatthepositionintheparalleldirectiontothetubeaxis,while<D）ａｎｄ(E)intheperpendiculardirection．Fig.２whichｃａｎｂｅｄｅｔｅｒｍｉｎｅｄｂｙｔｈｅｂｅａｍｌｉｍｉｔ‐ingdeviceTheionizationchamberwasplacedsothatthelongaxiscouldbeperpendiculartotheprimaryX-ray・Exposurewithintheradiationfieldwasmeasuredatthedifferentpositionsintwodirections；（１）paralleltothetubeaxis,ａｎｄ（２）perpendiculaItｏｔｈｅｔｕｂｅａｘｌｓ・ＡｓｓｈｏｗｎｉｎＦｉｇ､２，arrangementoftheminForwasChangedbyturningthebeamlimitingdevice・Intheparalleldirection，（A）therightendofthemirrorapproachｅｓｔｏｔｈｅｔｕｂｅ研（B)theposteriorendofthemirrorapproachestothetube，（C)theleftendofthemirTorapproacheｓｔｏｔｈｅｔｕｂｅ・I、thepeIpendiculardirection，nessTherefore，thetotalfiltrationofX-raysourceassemblyisequivalentt０２．５mmA1withhalf-valuelayerof2､45ｍｍＡ１ａｔ８０ｋＶ､AmirrDrisequippedinthebeamlimitingdevicewithainclinedangleof36degreestothehorizon‐talplaneThebeamlimitingdevicecanbeeasilymrnedaroundtheverticalaxisandamirrorChangesthepositionrelativetotheX-raytube．２．ＭｗＩＴＩＯＤＳＵｓｉｎｇｌＯＮＥＸｔｈｉｍｂｌｅｉｏｎｉzationchamber(volumeU6cc)，exposurewasmeasuredat80kV-200mA-0.2sec､Ｆｉｇｌｓｈｏｗｓｔｈｅｇｅｏｍｅｔｒｙｕｓｅｄｉｎｔｈｉｓstudy,Thetarget-to-chamberdis‐tancewaslOOcm,andthechamber-to-tabledis‐tancewas30clnThesizeofradiationfieldwasalwayskepttobe35cmx42.5ｃｍ(l4inchxl7inCh）becausethisisthemzuximumsizefOrmedicaluseandcorresPondswith82､4％ｏｆｆｕｌｌｓｉｚｅ－２４－Ｅ舵C/S〔ＷﾉｶejMｶﾞｸｎＰｗＰｂｓｊｊわれｏ〃'んＣＤ歯t減り"'わ〃q/･ＸγzZy吻陀"s均珈Ｒａｄｉｍわれ碇〃Ｔａｂｌｅｌ EJqDoBurewithintheradiationfieIdatlOOCmh⑪mthetaZg巴t,ａｎｄ８０kV･200ｍＡ－０．２sec.(A),(Ｂｈ(C),(D)and(E)are圏howninHg､２．Table２Ⅱ｡moBmcratiobetweenthediffC-rentmirTorpositioms．IEXposure(ｍＲ）!(B)－(A)(C)－(A)の)－囮）Ｉ（A）（A）（E）DiStancefromthecenterに、）Exposure(ｍＲ）~rEi￣ｉＥ１Ｔ面７．Ｉ２４２４１１６４７５７３１１７２．１１０１０６１１６７１５６１５２１１８６１８１１７９１１９２１９７１９７１１９７２０２２０６１１９７２０２２０８１１９６１９９２０７ｉｌ９４１６６１７４１１９１。、９９１０３１１７９Distancefromthecenterに、）Ｔｏｗａｒｄ＋21.3ｔｏｔｈｅ＋17.8anode＋15.8＋10.5＋５．２±０．０－５．２－１０．５ＴＯｗａｒｄ-15.8ｔｏｔｈｅ-17.8cathode-21.3㈹一型別“噸唖獅迦噸唖蠅犯⑥｜噸翅蠅ｍｍｍｍｍｍ噸、０３５９２００５１４６●●●ｂ●●●●●‐●■●０６３１２００１３６７一一一？’＋＋＋＋３８８５２０２５８８３●●●●●●●●●●■１７５０５０５０５７１２１１１１１１２＋＋＋＋＋＋’’’’’一Towardtotheanode０８０４２００５３５０●●ひ●●●●●●０００８７４３０２４７１２１１’一一一＋＋＋＋＋－５．２－６．０－１０．２－３．１－２．６０．０＋0.5＋２．６＋３．２＋４．４＋２．９Towardtothecathode（D）theposteriorendofthemilTOrappro‐ａＣｈｅｓｔｏｔｈｅｔｕｂｅ，（E)theleftendofthemirrorapproachestothetubeMeasunngsitewasrepresentedusingboththedistancefromthecenter，andtheanglefromtheverticallineasfO11owsThecenterwithintheradiationfieldis±0.0ｃｍｏｒ±0゜、Ｆｏｒｃｏｎ‐venience，Sake,thepositiontowardtheanodeinthedirectionparalleltothetubeaxis,ｏｒｏｎｅｔｏｗａｒｄｔｈｅａｎｔｅｒｉｏｒｅｎｄｏｆｔｈｅmirmrinthedirectionperpendiculartothetubeaxiswasrepresentedwithpositivecoordinate・Expo‐surewasmeasuredatthefO110wingposi‐tions；±0.0ｃｍ，±5.2ｃｍ，±10.5ｃｍ，±15.8ｃｍ，±17.8ｃｍａｎｄ±21.3ｃｍ，Thesepositionscorres‐pondｔｏ±0.,±3゜，±6.,±9.,±10.2゜ａｎｄ±12・inthepolarcoordinate．nent,althoughexposuredecreasedwithincreas‐ingdistanceFurthennore，exposurewasnotsignificantlyaffectedbymirrorpositionsExpo‐ｓｕｒｅａｔ２Ｌ３ｃｍｏｒ-21.3cｍｗａｓｌ６４ｍＲｏｒｌ７９ｍＲｉｎ（D)，ａｎｄｌ７３ｍＲｏｒｌ７４ｍＲｉｎ（E),respectively､Table2showspercentagedifferencesofX-rayintensityamong(Ａ),(B),(C),(D)ａｎｄ(E)．Themax1mumdifferencewasｓｈｏｗｎａｔｔｈｅｐｏｓｉｔｉｏｎｏｆ－２Ｌ３ｃｍｔｏｂｅ7.6％between(Ａ)ａｎｄ(B),ａｎｄ12.0％between(Ａ)ａｎｄ(C).Therefore，iｆｔｈｅｍｉｒｒｏｒｉｓｐｌａｃｅｄａｔ（A)，ｔｈｅimprove‐ｍｅｎｔcanbeexpectedwithUniformilyofl2.0%・TheX-rayintensityattheconstantdistancefromthefocuswithvariousangleswascalcu‐latedbytheinversesquarelawEx＝EC・〔1002＋(±Ｘ)2〕/1002 （１）whereXisthedistancefromthecenter(c、)．Existheexposureateachposition(±Ｘｃｍ)andEoistheexposureatthecenter・ＴｈｅｓｅｖａｌｕｅｓａｒｅｓｈｏｗｎｉｎＦｉｇ,３ａｓｔｈｅｍｔｉｏｔｏｔｈｅｖａｌｕｅａｔｔｈｅｃｅｎｔｅｒ・Ｔｈｅａｒｅａｓｈｏｗｉｎｇ９０％ｔｏ１１０％ofexposureatthecenterranged4･ｔｏ-10゜ｉｎ(A）ａｎｄ(B),ａｎｄ3.5゜ｔｏ-11.ｉｎ(C),whilel2oto-12･ｉｎの)ａｎｄ(E).TherefOre,(D)ａｎｄ(E)showedthewidestarearanging＋12゜ｔｏ－１２．，althoughthevalueatbothedgestowardtheanodeandthecathodedecrcasedsigni‐ficantlyascompar℃ｄｗｉｔｈｔｈａｔａｔｔｈｅｃｅｎｔｅｒ・ＡｓｓｈｏｗｎｉｎＦｉｇ３,intheparallelorperpendi‐culardirection，ｔｈｅａｒｅａｓｈｏｗｉｎｇ９０％ｔｏ１１０％RESILTSTablelshowsexposureinthedirectionsbothparallelandperpendiculartothetubeaxls・ExposurewithintheradiationfieldwasaffectedbythedifferentmirrorpOsitionsln(A),(B)ａｎｄ(C)，exposureatthepositivecoordinatedecreasedremarkablywithincreasingdistancefromthecenter，Exposureat＋21.3cｍｏｒ－２Ｌ３ｃｍｉｎ（A）ｗａｓ２４ｍＲｏｒ９２ｍＲ，respect‐ively・Tothecontrary,ｉｎ(D)ａｎｄ(E),theeffectofdistancefmmthecenterwasn，ｔｓｏｐｒｏｍｉ‐－２５－７ＫＫｂＷＺｊｈｚ,ｅ'ａＬ、(岸催 ノ！ （ （ E）＄８ ８ ８0％1００ 1００ １００。 ｡ 「．Ⅱ -If-I9-Io-j･Ｉｏ１ｊ。}I･ｌＭＩFig.３ DiBtributionofX-myintenBityontlBepolarcoordimteBatlOOcm企omthefOcugandwitlwario頤angUestothecentralray．Ａ,Anode.；Ｍ,Mirror.(A),(B),ａｎｄ(C）ｓｈｏｗmeasurementatthepositionsinthedirectionparalleltothetubeaxis,whileの)ａｎｄ(E)perpendiculartothetubeaxis．(B),3.5゜ｔｏ-11゜ｉｎ(C),ａｎｄｌ２ｏｔｏ－１２゜ｉｎ(D）and(E).Itshouldbenotedthatthemaximumintensityareaandtheareashowing90％ｔｏ110％ofeXposureatthecentershiftedfromthecentertowardthecathodeintheparalleldirection,ｏｒｔｏｗａｒｄｔｈｅｐｏｓｔｅｒｉｏｒｓｉｄｅｉｎｔｈｅｐerpendi‐culardirectionTheareashowing90％ｔｏ110％isregardedashomogeneousintensityarealnthediscussionofX-rayintensity,wehavetotakeaccountofinherentfiltration，theabsorptionofX-raybytargetitselfandthick-nessofamilTor・FirsUy,inherantfiltrationisdefinedasthefiltrationofmaterialsbetweenthetargetandtheexteriorofthetubeafterallthematerialsinthebeamhavebeenremoved，butthetubehasbeenremainingoperationaLThereisnostandardmethodformeasunnginherantfiltrationofintacttubes3).Secondly，X-raythatoccurreddeeplytothesurfaceofthetargetaremoreheavilyfilteredbeforeleavingthetarget､Thisphenomenoniscalledthe“heel，，effectandinfluencesX-rayqualityaswellasX-rayintensity・Lastly，thicknessofamirrorchangesaccordingtotheangleatwhichX-raysareemittedbecauseamirrorisobliquelｙｅｑｕｉｐｐｅｄｏｎｔｈｅｗａｙｏｆｔｈｅｐａｓｓａｇｅｏfX-ray・Themirrorusedinthisstudyinclined36degreestOthehorizontalplane，Thereforeatofexposureatthecentershiftedtowardthecathodeortheposterior・Themaxlmuminten‐ｓｉｔｙｗａｓｓｈｏｗｎａｔ－３。，－６゜，－９．，－９゜ａｎｄ±0°ｉｎ(A),(B),(C),(D),ａｎｄ(E),respectively．DISCUSSIONThepositionofbeamlimitingdevicerela‐tivetotheX-raytubecanbechangedaccordingtokindsofradiographyandpositioningofpatients，andsoonSimultaneously，amirrorwithwhichthebeamlimitingdevicehasequiP‐pedalsOchangesthepositionrelativetotheX-raytube､SinceamirmrisobliquelyinsertedonthewayｏｆｐａｓｓａｇｅｏｆＸ－ｒａｙｂｅａｍ，whichwasweakenedaccordingtothedistancefromthefOcus，penetratesthemilTorwiththedifferentintensity・Therefore，thechangeofmirrorpositioncausestheheterogeneousdis‐tributionofX-rayintensityanddegradestheimagmgquality、Inordertodecidethebestpositionofthemirror,westudiedtheeffectsofmirrorpositiononthedistributionofX-rayintensitywithintheradiationfieldlnourresultsthemaximumintensiｔｙａｒｅａｗａｓｓｈｏｗｎａｔ－３．，－６．，－９．，－９゜，ａｎｄＯ・ｉｎ(Ａ),(B),(C),(D),ａｎｄ(E),r巳spectivelyFurther‐more,ｔｈｅａｒｅａｓｈｏｗｉｎｇ９０％ｔｏ110％ｏｆｅｘｐｏ‐sureatthecenterranged4oto-10．ｉｎ(Ａ)ａｎｄ･－２６－助bcjsqﾌﾟｵﾙeMH)'７℃γ"s"われｏ〃ﾒｶＣＤだ'が6ｍわれq/正ｍｙ"…s吻劾Ｒ(zditztjo〃Ｆ泥〃小 tuswithoutbeamlimitingdevice・Hereportedthatchangesinoutputwereproducedbyfiltra‐tion，andindicatedthatthequalityofradiationalsovariedwiththeanglefiomthecentralray・ArdranG,Ｍｅｔａｌ3）reportedtheeffectoftargetangleonX-rayqualitywiththeinhe‐rentfiltrationandconcludedthatthetargetangleofthetubehadtheimportanteffectinalteringX-rayquality・Fromourresults,itwasconsideredthattheshiftofthemaxlmumandhomogeneousareatowardthecathodewascausedbytheheeleffectOntheotherhand,althoughthearrange‐mentｉｎ(D)did､'trdatetoheeleffect,themaxi‐mumandhomogeneousareashiftedtowardtheposteriorside・Thisshiftwasconsideredtobeduetotheeffectsofamirrorposition・ThemaxlmumdifferenceamongvanousarTange‐mentofamilTorwas12.0％intheparalleldirec‐ｔｉｏｎＡｍｉｒｒｏｒｅｘｉｓｔｉｎｇｏｎｔｈｅｗａｙｏｆｔhepassageofX-rayweakenstheintensityandactsasafilter､ThisactionisenhancedagainstweakX-ray．Ｉnordertogethomogeneousdistribu‐tion，amirrorshouldbeplacedattheposi‐tionwhereX-raywithhighintensitypenetratesthethiCkpartOfamirror､Therefore,(A）seemstobethemostappropriateposition〆Inconclusion，wheneverwetakearadio‐graphy，wealwaysshouldconsidertheposi‐ｔｉｏｎｏｆａｍｉｒｒｏｒｉｎｔｈｅｂｅａｍｌｉｍｉｔｉｎｇdevice．e（゜） １．１０』３』６．９ユロ０４ユ ０．９６５ユ．089 ０．９３４ユ．１４４ ０．９０８1．1５４ﾕ０．２ ０．９００ユ．２０９ﾕ２ ０．８８５FYg、４ Relation8hipbetweentheanglefromthevertiCaIIineandrelativeｔｈｉｄｍｅｇｇｏｆｔｈｅｍｍｏｒ．Ｆ，Focus.；Ｍ，Mirror．lZinthepolorcoordinate,thicknessofamirmratthenear,orfarlocationversusthecentralthicknesswascalculatedtobeO885，ｏｒ1.209,respectively(Fig.4).Thisdifferencecan'tbeignoredonthediscussionofX-rayintensity，Someauthors1-3)reportedontheX-rayinten‐sityWithintheradiationfieldandfiltrationHowever，theydidn'tdiscusstheeffectofamirrorposition､CooligeWD・ｅｔａｌ１)describedthatwithoutfilter,themaxlmumintensityfromthebackofthethrgetwasl1.1％ｏｆｔｈｅｍａｘｉ‐ｍｕｍｆｒｏｍｔｈｅｆｒｏｎｔｏｆｔｈｅｔａｒｇｅｔ；with3mmand6mmofAlfilteritwasl0.4％ａｎｄ9.0%,res‐pectively、ZintheoCJ2）investigatedthatthevariationintheX-rayoutputwasaffectedbytheａｎｇｌｅｔｏｔｈｅｃｅｎｔｒａｌｒａｙｕｓｉｎｇｔｈｅａｐpara‐ＲＥＦＥＲＥＮＣＥＳ１）Coolidge,ＷＤ.,Kearsley,ＷＫ.：HighvoltageX-rayworkAm.J・Reontgenal.＆RadThera.,９:77-101,1922.2）Zintheo,ＣＪ.：Variationsintheintensityandqua‐lityofreontgen-rayoutputasaffectedbytheangletothecentralray,therEontgentubeandther巳ontgenmachine.Ａｍ､JReontgenaL＆Ｒａ｡.Ｔhera.,37:98-104,1937.3）Ardran,ＧＭ.,Crooks,ＨＥ.：Themeasu正mentofinherentfiltrationindiagnosticX-raytubesandeffectoftargetangleonX-rayquality・Ｂｒit.Ｊ・Radio1.,45：599-602,1972.－２７－ＫＫＤｓ〃jZjtz,ｅｍＬ ’照射野内のＸ線強度分布に及ぼすミラー位置の影響越田吉郎，高山輝彦要旨Ｘ線発生装置の照射野限定部には，光学的照射野とＸ線照射野を一致させるためにミラーが取り付けられている．このミラーの位置がＸ線強度に及ぼす影響について検討した。Ｘ線管の管軸と平行方向の陽極側の位置では，中心からの距離の増加につれてＸ線強度は著明に低下した。しかし，管軸に垂直方向では中心からの距離の影響は平行方向ほど著明でなかった。Ｘ線強度が均一分布を示す領域は，管軸に平行な方向では陰極側へ移動し，垂直方向では後側に移動した。またミラーの陽極側が陽極に近づく配置では，最も均一なＸ線強度分布を示したが，陽極から遠ざかる配置では，最も不均一な分布を示した。ミラーの陽極側が陽極に近づく位置に配置すると，均一性が改善した。以上より，照射野内のＸ線強度分布は，ミラーの位圃によって影響されることから，撮影に際しては照射野内のＸ線強度を均一にすザるために，ミラーの位置について考慮しなければならない。2８

照射野内のX線強度分布に及ぼすミラー位置の影響

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照射野内のX線強度分布に及ぼすミラー位置の影響

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