Whatarethesideeffectsoftreatment?Side effects can develop when normal tissues recieve radiation.Thetypesofsideeffectsseenwilldependonmanyfactorssuchastheareatreatedandthegoalofthetreatment(definitive,palliative,stereotactic).Forsometreatments,thesideeffectscanbenotable,whilstforothersnosideeffectsareseen.

Therearetwotypesofradiationtherapysideeffects:acuteandlate.

Acutesideeffectsoccur duringorshortlyafterthecompletionof radiationtherapy–typicallystartinginthesecondorthirdweekoftreatmentandlast2–4weeks.Whileacutesideeffectsarecommon,theyaregenerallytransientandself-limiting;resolutionwilloccuroverthefollowingweeks.Rarely sideeffectsareprolonged as aresultofbiologicvariation.Acutesideeffectsareseenmostcommonlyintissuesthatrapidlydivideandhavetheabilitytorepairthemselves(skin,oralmucosa,liningofthegastrointestinaltract,andfootpads).Whilesideeffectsareresolving,wesupportourpatientswithpainmedicationsandothersupportivecare.Symptomatictherapyandpatienceisgenerallythebesttreatmentandcaremustbetakennottodamagethetissuesfurther(animalscratching,orhumanscrubbing).Onrareoccasionafterradiationofnervoustissue(brainorspinalcord)acuteedema(swelling)mayoccurandmustbetreatedwithcorticosteroidsuntilsymptomsresolve.

Left. A poodle 2 weeks afterradiationforatumorinthenasalcavity and sinuses. Note thealopecia (hair loss). Right, thesame patient 3 months aftertreatment. Note the hairregrowth. Often hair regrowswith less pigment (white). Alsonote the black hair remainsaround his eyes indicating theaccuracyofTomoTherapy.

Latesideeffectsoccur6monthsorlaterafterthecompletionofradiationtherapy.Latesideeffectsareseenintissuesthatareslowlydividing.Asthecellscannotreplicateorrepairthemselvesreadily,radiation-induceddamagecannotberepairedaseasily.Unlikeacutesideeffects,whicharecommonandself-limiting,lateeffectsaremuchlesscommon(rare).Whenlateeffectsoccurtheyhavethepotentialtobeseriousandcanbepermanent.Latesideeffectsaretypicallyseeninconnectivetissues(bone,nervoustissue,andcartilage),skinandeyes.Morespecificallywecanseemusclefibrosis,skinfibrosis,bonenecrosisandfracture,orradiationinducedsecondcancersthatcan(rarely)occurseveralyearsafterradiationtherapy.

The risk of specificsideeffectscanoftenbecontrolled with thoughtful radiation planning.Thesesideeffectswillbediscussedwithyouonanindividualbasis.OurTomoTherapyunitsignificantlyreducestheincidenceandseverityofsideeffectsseenduetopreciseradiationdelivery.StudiesperformedhereattheVeterinaryMedicalTeachingHospitalhaveindicatedsignificantlyreducedocular(eye)sideeffects in dogs treated for nasal tumors.

Overall,whatisthelikelihoodyourpetwillexperienceradiationsideeffects?Becauseofpatientandtumorvariations,wecannotaccurately predictwhichpatientswillorwillnotexperiencesideeffectsandtowhatdegreetheywilloccur.Althoughacutesideeffectsarecommonandoccurtosomedegreeinnearlyallpatients,theyaregenerallyself-limitingandtransient.Latetermsideeffectscanbemoreseriousandpermanent;however,ourdosingscheduleisaimedatminimizingthelikelihoodoflatesideeffects.Thelikelihoodofaseriouslatesideeffectislessthan5%.

Whileradiationtherapycan causesomediscomfortintheshortterm,thegoalisforourpatientstohaveagoodqualityoflifefollowingtreatment.