Radiation Effects in the Lungs
RadiationEffects in the Lungs
Thelung is madeup of morethan 40 differenttypesof cells,andwhilemostof theseare regardedas radioresistant, theeffectsof radiationon thesecellsare an involvedonesince thelungs are complexbodyorgan(Coggle, Lambertn & Moorest 263).Thelungs as a completeorganpossessverylimitedregenerative capabilityandas suchitcan not be ableto putup with veryhighdosesof radiation.In fact,theradiosensitivity of thecellsliningthewallsof thelungs istheprimarylimiting elementsin radiotherapy of thetorso.Thegravedamagethatin duecourseleadto impairedventilationanddiffusioncapacityare connectedto thelevel of doseused,thefractionation of thedose,to thetotalvolumeof thelung that is under radiation(N.I.H 1).Theabsorptionof ionizing radiationleadsto instantsubcellular, biochemical andcellular impairment whileits morphological expressionin relationto thetotaltissuedamageandorgandysfunction are oftensignificantly tardy.Radiationinjuryto thelung can beexpressedat alllevels of theorganizationfrom simplest,molecularlevel to themostcomplex,theorganlevel (Coggle, Lambertn & Moorest 5). Thereactionof thelung has beenexaminedhistologically, biochemically, pathologically, cellkinetically andphysiologically usingthelung demiseas theendpoint. Thereviewshall exemplifytheradiationeffectson thelung by examiningreactionsof thelung to bothinternalandexternalradiation,includingcarcinogenesis, pneumonitis andfibrosis (Coggle, Lambertn & Moorest 265).
Effectsof Radiation in theLung
Asmentionedabove thelung is constitutedby cellsthat havedifferentdegreeof radiosensitive, nonethelesshighradiationdosecan affectall thecellsof thelung. In thisregards,thispartshall onlyexamineacuteeffectsof radiationin thelung. Latereactionof thelungs to exposureto radiationcan be separatedinto two focal typesof syndromes,which are not relatedin anywayradiationpneumonitis which crops up 6 monthsafter theexposureto radiationandradiationfibrosis which is a lateresponsethatcropsup between the6-12 monthafter exposurehighdosage of radiation(Coggle, Lambertn & Moorest 270).
RadiationPneumonitis and Radiation-inducedpulmonaryfibrosis
Radiationpneumonitis is thechronicmanifestationof radiation-induced lung disease,anditnormallycrops up after chestwallradiotherapy. Radiation-inducedpulmonaryfibrosis is thelatemanifestationof radiationto thelungs andis commonin individualswhohaveundergonethrough intrathoracic malignanciesandchestradiotherapy. RadiationPneumonitis occursdue to thedeathof thecellsandthedepletionof cellpopulationand in conditionswhenradiationhampersadequateregenerationof theparenchyma. (Coggle, Lambertn & Moorest 276). Clinically,fibrosis occursdueto bothinternalandexternalexposureto radiations.Forexample,acutex-ray dosescan leadtosubstantialfibrosis in human.Dosesthatare largerthan 20-30Gy can causesignificantfibrillar connective tissuedeposition.Fibrotic is a termthat is usedto denotetheincreaseof theconnective tissuefibersin reactionto someinsultsuchas exposureto radiation(Merrill 1). Radiation pneumonitis has been stated to account forabout 34 percent of all patients that received chest radiation. Asmentioned above the occurrence of radiation pneumonitis and fibrosisis dependent on the volume of the lungs exposed to radiation, totaldose irradiated and fractionation (N.I.H 1).
Thedemographics of individualswhodevelopradiationpneumonitis are thoseof theprimaryconditionforwhich radiationtherapyisdone.Under normalcircumstancepatientsreceiveradiationtherapybecauseof thefollowinghealthproblems.Necknodal diseaseBreastcancerBronchogeniccancerOesophagealcarcinoma
Theriskof developingradiationpneumonitis ispeggedon a numberof elementssuchasDegreeof fractionation, level of doseadministeredrare below20Gy andis nearlyinvariableabove 40Gy, Pastchemotherapy (N.I.H 1). Since pulmonaryfibrosis promptedby radiationto thelungs is a latestageof radiation-induced lung diseaseitepidemiologys synonymousto thatof theradiationpneumonitis.
Thissyndromecan bedividedinto two phasesthat are distinct,butthatoverlapone another.(a)Thefirstphaseis thelatentperiodthat lastfor5 one monthafter exposureto moderatedoseof radiation.Averagedoseof radiationrangesbetween -10-15 Gy andis salientfeaturesare theabsenceof grosshistoricaldamage.(b)Exudative phasethat last3-8 weeksafter radiationexposureandwhich istypifiedby proteinrichdepositsin theairspacesandmassivethiningof theendothelial andepithelial celllining.Thisphaseonlyexistswhenthere is exposureto highradiationdose,normallyabove 10Gy (Coggle, Lambertn& Moorest271).(c) ThethirdphaseI referredto as acutepneumonitis that crops up between thesecondandthesixth monthafter radiationexposureandischaracterizedby edema of thelung airspacesandthealveolar septa. Desquamative alterationsarisein endothelial andepithelial cellswith increasednumberof mononuclear inflammatorycellsin theairspacesandsepta.(d) Thelastphaseis referredto as thechronicphaseandoccursfrom thesixth monthonwards andentailstheregenerationandrepairproliferationof alveolar andseptal cellsthat resultin subtlereconstructional alterationsin vascular, septal andconnective tissues.Radiationpneumonitis isnormallyregardedas theinflammatoryresponsethat advancesto a chronicfibrotic reaction.Bothcasescan leadto death(Coggle, Lambertn& Moorest271).
Symptomsnormally develop from the first to the third month after exposure toradiation, with fibrosis happening 6-12 months. Dyspnea out offraction to the lung volume exposed to radiation is the mostprevalent symptom, and occurs to 90 percent of individual exposed toradiation. Cough which is normally nonproductive, affects 50-60percent of the patients. Mild fever is also reported in some patientsas well (N.I.H1).The following are the general symptoms that develop in most patients7-10 days after exposure to radiation:
Pleuriticpain VolumelossMediastinal shift LinescarringPleural thickening Ipsilateral pleuraleffuse TractionbronchiectasisChestdiscomfortDyspnoeaCoughLowgradefever
Whenthe diagnosis of both radiation pneumonitis and fibrosis is made,then an individual can be treated fairly effectively withsteroids.Steroids can be usedto lessentheseverityof radiationpneumonitis.Based on theextentof theinjuryto thelungs, alterationsmay be benignandspontaneouslyprogressrespiratory distresssyndrom(N.I.H1).
Oralcorticosterioids have been the most common drugs used in the courseof radiation pneumonitis therapy. At the moment there is no adequatehuman study to support the efficiency of this drug but the clinicalhistory point that corticosteroid have a reaction rate as high as 80percent in improving symptoms.Angiotensin which is a drug thatconverts enzyme inhibitors to harmless compounds has been reported toinhibit radiation pneumonitis.
Pentoxifyllinewhen used together with vitamin E has been shown to alleviateradiation-induced skin alteration. Fibrosis is an irreversibleprocess and can not improve even when the drugs mentioned above areused in therapy. Whenthehistoryof theexposureto radiationisknown,differentialdiagnosismay be donebased on thedominantsigns.Fibrosisis thelateof radiationlung diseaseandat themomentthere is treatmentavailableforthiscondition.Theonlyoptionis to follow-up to assesfortumourrecurrence (N.I.H 1).
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Coggle,E. John Lambert, E. Barrie and Moorest, R. Steve. Radiation Effectsin the Lung. EnvironmentalHealth Perspectives.2006. Vol. 70, pp. 261-291.
Merrill,W.William (MD).Radiation-inducedlung injury.Medical University of South Carolina. 2014.Web. 24 JAN. 2015. http://www.uptodate.com/contents/radiation-induced-lung-injury#subscribeMessage.
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