InadditiontoaffectingDNAandnuclei,radiantenergymayinduceavarietyofcytoplasmic changes, includingcytoplasmicswelling,mitochondrialdistortion,anddegenerationoftheER.Plasmamembranebreaksandfocaldefectsmayappear.Thehistologicconstellationofcellularpleomorphism,giantcellformation,changesinnuclei,andmitoticfigurescreatesamorethanpassingsimilaritybetweenradiation-injuredcellsandcancercells,aproblemthatplaguesthepathologistwhenevaluatingpost-irradiationtissuesforpersistenceorrecurrenceofcancer.
Atthelightmicroscopiclevel,vascularchangesandinterstitialfibrosisareprominentinirradiatedtissues(
Fig.8.15 ).Duringtheimmediatepostirradiationperiod,vesselsmayshowonlydilation.Later,orwithhigherdoses,avarietyofdegenerativechangesappear,includingendothelialcellswellingandvacuolation,orevennecrosisofthewallsofsmallvesselssuchascapillariesandvenules.Affectedvesselsmayruptureorundergothrombosis.Stilllater,endothelialcellproliferationandcollagenoushyalinizationwiththickeningofthemedialayerareseeninirradiatedvessels,resultinginmarkednarrowingorobliterationofthevascularlumina.Atthistime,anincreaseininterstitialcollagenintheirradiatedfield,leadingtoscarringandcontractions,usuallybecomesevident.
Fig. 8.16 depicts the main consequences of radiation injury. As already mentioned, the most sensitive organs and tissues are the gonads, the hematopoietic and lymphoid systems, and the lining of the GI tract. Estimated threshold doses for the effects of acute exposure to radiation in various organs are shown in
Table 8.7 . The changes in the hematopoietic and lymphoid systems, along with cancers induced by environmental or occupational exposure to ionizing radiation, are summarized as follows: • Hematopoietic and lymphoid systems. The hematopoietic and lymphoid systems are extremely susceptible to radiation injury and deserve special mention. With high
Embryonic – destruction of neurons and glial cells (weeks to months)
Erythema, edema (early)
Dyspigmentation (weeks to months) (months to years)
Interstitial fibrosis (months to years)
Fibrosis of wall (late)
Atrophy and fibrosis of gonads (late)
Table 8.7 Estimated Threshold Doses for Acute Radiation Effects on Specific Organs 0.15 0.50
Reversibleskineffects(e.g.,Skin1.0–2.0erythema)
PermanentsterilityOvaries2.5–6.0