WhataretheGoalsofRadiationTherapy?DefinitiveRadiationTherapy

Definitive intent radiation therapy aims tominimize the long-term adverse effects ofradiationtherapyandtoenhancethe long-termcontrolofthecancer.Definitiveintentradiationtherapygenerallymeansthatsmalldosagesofradiationareadministereddailyover 2 to 4 weeks. By giving many smalltreatments of radiation we can ensure alarge total dose of radiation is safelyadministered. This increases the likelihoodof long term tumor control andminimizesthe chance of long term complications.Therearesometumortypesthataretreatedwithdefinitiveintent,howevertheyrespondbetter to less frequent dosing (i.e.melanoma).

PalliativeRadiationTherapyPalliative radiation therapy aims to relievecancer relatedpain and improvequality oflifeinpatientsratherthanprovidelong-termtumor control.This type of treatment may be used for any patient with tumor-related clinical signs such as discomfort or bleeding.It is particularlyeffectiveinalleviatingpainincasesofbonecancer.Thetreatmentschedulesarelessintenseandlessexpensive.

StereotacticRadiationTherapy (SRT or SBRT)Stereotactic radiation therapy is a highlyspecialized technique that delivers a singleor fewhighly conformal doses of radiationto a tumor with submillimeter accuracy. Ithas also been called stereotacticradiosurgery (SRS) as the high degree ofaccuracyissimilartowhatcanbeachievedwith a surgical scalpel blade. Due to thehighdosesadministeredpertreatment,itisessential to accurately localize andimmobilize the tumor. Localization isachieved by imaging at the time theradiation is delivered and with positioningdevices (mouth molds and bodymattresses). The TomoTherapy unitperforms a CT scan of the region to betreated before every treatment to ensureprecise set-up of the patient for accurate radiationdelivery.

The tumor must be well circumscribedmakingtreatmentofsometumortypes(e.g.thosewhicharevery invasiveor large) lessappropriate. For some typesof tumors theintent of stereotactic radiation can becurative(e.g.braintumors)whilstforothersitcanbeviewedaspalliative.

There is intense interest in stereotacticradiationtherapyinveterinarymedicineasitgenerally involves fewer treatments andthereforefeweranestheticevents and visits to the hospital.

TomoTherapy is specifically designed todeliverstereotacticradiationtherapy.

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Images.ThefirstimageindicatestheexquisitedoseconformityachievedwithTomoTherapyinabonetumor.Thesecondimageisacrosssectionofanasaltumorin a dog showingavoidanceofthebrain.Thethirdimageisavertebraltumorshowingavoidanceofthespinalcord, lungsandheart.Thefinal imageisanasaltumorshowingavoidanceof botheyes.Allcasesweretreated with SRT