Thisparticularmethodoftreatmentwasdiscoveredbyaccident:In1903,twoforeigndoctorstreatedapatientwithskincancer.Sinceitwascertainthattherewasnosymptomaticmedicine,andinordertocomfortthepatientmentally,somedyecalledeosinwasappliedtotheaffectedareatohelpreduceinflammation.Afewdayslater,thepatientcametoseethedoctoragain,andthedoctorunexpectedlyfoundthatthecancerhadshrunk.Afterunderstanding,thepatienthasnotusedotherdrugsandeverythingisnormalinlife,exceptthatheisbaskinginthesuneveryday.Afterstudyingtheseconditions,thedoctorbelievedthatitwastheeffectofeosindyeandsunlight,sohefurthertestedandfoundphotosensitivity.However,theuseofphotosensitivetechnologytotreatcancerhasnotmademuchprogress.Thereasonwasthatthephotosensitivematerialselectedatthattimewasnotsatisfactoryandtherewasnoideallightsource.
In1960,LipsonintheUnitedStatessucceededinresearchingaphotosensitivesubstancecalledHPD,andphotosensitivetechnologywasdeveloped.Thissubstanceisextremelyclosetocancercellsandhugstogetherwhentheymeet.Afteritwasinjectedintothehumanbody,twoorthreedayslater,theHPDinthenormaltissueswasexcreted,buttherearestillalotofcancertissues,anditcanemitfluorescencewithashort-wavelengthlight.Thisprovidesapowerfuldiagnostictoolfordoctorstocheckwhetherapatienthascancer.Furthermore,byirradiatingcanceroustissuescontainingHPDwithorange-redlight,HPDundergoesachemicalreactiontoproducemonoatomicoxygen,whichcannecrosisthecancercelltissues;HPDhasbeenexcretedfromnormalcelltissuesinotherpartsofthehumanbodyandwillnotbedestroyed.
