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Stereotactic Body RadiationTherapy (SBRT) – OneDosimetrist’s Experience
SBRT DefinitionWhat is SBRT? StereotacticBodyRadiationTherapy
SBRT DefinitionStereotactic Stereotaxy the superposition of a 3Dco-ordinate system upon a given organor structure. Requires an external frame, fixed to thebody and treatment apparatus. The cranium is really the only site thisis practical for.
SBRT Definition
SBRT DefinitionBody This seems like an odd descriptor ofradiation therapy isn’t it all given tothe body? Body Extracranial
SBRT DefinitionRadiation Therapy Hopefully, we all have some idea whatthis is or do we ?
SBRT DefinitionStandard Radiation Therapy Developed over the last 70 years Fractionated Daily Dose 1.8 – 2.0 Gy 2 – 4 Fields
SBRT DefinitionStandard Radiation Therapy Functions by disrupting cellular division Cellular division is a complex process Disruption of any part of this processcan lead to loss of reproductiveintegrity “Multiple high-value targets”
SBRT DefinitionStandard Radiation TherapyMeyer, et al. 2007
SBRT DefinitionStandard Radiation Therapy Why fractionate? Normal Tissue Increasing dose / fraction using traditionaltechniques usually leads to increasedtoxicity Traditional techniques included too muchnormal tissue
SBRT DefinitionSBRT Delivery of high dose in few fractions SBRS (Stereotactic Body RadioSurgery) 1 fraction SBRT 2 – 5 fractions
SBRT DefinitionSBRT Functions by destroying target cellularfunction Any individual cellular function istypically simpler than cellularreproduction but all of functionalitymust be destroyed “Cumulative loss of low-value targets”
SBRTSBRT We need to be able to deliver highdose / fraction without toxicity Changes to Simulation Treatment Planning Treatment Delivery
SBRT SimulationSBRT Simulation Immobilization Body frames / bags – indexable High resolution CT (0.25cm or less) Respiratory Motion Compression plates / wraps Respiratory Gating – prospective orretrospective
SBRT DeliverySBRT Treatment Delivery High accuracy daily target localization IGRT CBCT kV / MV imaging Ultrasound
SBRT Treatment PlanningSBRT Treatment Planning High accuracy target definition Internal Target Volume (ITV) constructionconsidering the role of respiratory motion Highly conformal dose volumes Multiple beams (7 – 11), IMRT, VMAT Sharp dose gradients Small field sizes, dose prescription to lowisodoses, acceptance of doseinhomogeneity inside target
RPCI SBRT Experience Started our SBRT Lung program in2007 We also treat: LiverAdrenal / KidneySpinal MetastasesHead and Neck As of Sept 1 2016 – 536 cases
Lung SBRT Experience Lung SBRT (approx. 90% of cases) Follow RTOG protocols 0236 0813 0915 Developed internal protocols andclinical trials based upon the RTOGstudies
Lung SBRT Guidelines Target Definition ITV is constructed based upon evaluationof the respiratory motion Binned into 10% increments of respiratorycycle Segments with too much motion are notused for ITV generation and will not betreated PTV ITV 0.5cm
Lung SBRT Guidelines Dose Constraints – Target High conformality, sharp dose gradients Dose is typically prescribed to the highestisodose value that: Covers 95% of PTVIs between 60% and 90% of prescription dose Why 60 – 90%? Field conform to target with virtually no margin- 95% cannot cover volumeField sizes must be kept as small as possibleto spare normal tissue
Lung SBRT Guidelines Dose Constraints – Target High Dose Conformality 95% of PTV covered by 100% of prescriptiondose99% of PTV covered by 90% of prescriptiondose High Dose Spillage 100% Conformality Index Ratio of prescription dose volume / PTV volumeless than 1.2Volume of tissue outside the PTV exceeding105% must be less than 15% of PTV volume
Lung SBRT Guidelines Dose Constraints – Target Low Dose Spillage 50% Conformality Index Ratio of 50% prescription dose volume / PTVvolumeValue varies based upon PTV volumeLower acceptable limit as PTV volume increasesRange 2.9 – 3.9Maximum Dose 2cm from PTV Value varies based upon PTV volumeHigher acceptable limit as PTV volume increasesRange 46.8 – 73.8 % rx dose
Lung SBRT Guidelines Dose Constraints – Organs at Risk Standard dose constraints don’t work dueto: High dose / fractionDifferent mechanisms of cell damage Data from earlier protocols that resulted in“good” plans was used to determine doselimits, which are then modified accordingto total prescription dose
Lung SBRT Guidelines Dose Constraints – Organs at RiskConstraintsRTOG 023660 Gy / 3 FxRTOG 0813 RTOG 091550 – 60 Gy / 34 – 48 Gy /5 Fx1 – 4 FxRPCI I-12440730 – 60 Gy /1 – 3 FxLung V2010 %10 %10 %10 %Lung V71500 cc1500 ccLung V7.41000 cc1000 cc14 / 26 Gy14 / 18 Gy1.2 cc1.2 ccLung V12.51500 ccLung V13.51000 ccSpinal Cord MaxSpinal Cord V13.5Spinal Cord V718 Gy30 Gy0.5 cc
Lung SBRT vs 3DCRT Planning TechniquesStandard 3DCRTSBRTPrescription60 – 66 Gy30 – 60 GyDose / Fx1.8 – 2.0 Gy10 – 30 GyGTV / ITVDetermined byFree Breathing /Breath Hold CTRespiratory PhaseAnalysisPTVGTV 1.0 – 1.5cmITV 0.5cmTechnique2 – 4 Fields7-11 FieldsBlock Margin0.8 – 1.2cm0.0 – 0.2cm
Lung SBRT vs 3DCRT Targets3D CRTSBRT
Lung SBRT vs 3DCRT 95% Isodose Coverage3D CRTSBRT
Lung SBRT vs 3DCRT 50% Isodose Coverage3D CRTSBRT
Lung SBRT vs 3DCRT Low Dose Coverage (7 Gy)3D CRTSBRT
My SBRT Experience Started planning Lung SBRT in 2009 Started planning much more frequentlyin 2011 Presentation Data 70 cases2011 – 20163D and VMATHeterogeneity On and Off
My SBRT Experience Data Analysis Parameters vs Time – did I get any better?Parameters vs Technique – is VMAT better?Parameters vs Calculation – is Heterogeneitybetter?Parameter vs Patient Characteristics – is therea relationship between:––PTV volume and dose coverageTotal lung volume and lung parameters
My SBRT Experience Did I get any better?
My SBRT Experience Did I get any better?
My SBRT Experience Did I get any better?
My SBRT Experience Did I get any better?
My SBRT Experience Is VMAT better than 3D?3D (n 57)VMAT (n 13)Conformality Index / Limit0.900.83 **Max Dose PTV 2cm / Limit0.970.94V50% Rx Dose / Limit0.910.99Lung V7 / Limit0.270.46 **Lung V20 / Limit0.300.40 **Time on Treatment Couch35.515
My SBRT Experience Is Heterogeneity correction better? We plan patients with or without heterogeneitycorrections based upon the protocol we arefollowing and/or the treatment techniqueProtocolHeterogeneity CorrectionRTOG 0236NRTOG 0813YRTOG 0915YRPCI I-124407NAll VMAT casesY
My SBRT Experience Is Heterogeneity correction better? We plan patients with or without heterogeneitycorrections based upon the protocol we arefollowing and/or the treatment techniqueProtocolHeterogeneity CorrectionRTOG 0236NRTOG 0813YRTOG 0915YRPCI I-124407NAll VMAT casesY
My SBRT Experience Is there a relationship between PTVvolume and dose parameters?
My SBRT Experience Is there a relationship between PTVvolume and dose parameters?
My SBRT Experience Is there a relationship between PTVvolume and dose parameters?
My SBRT Experience Is there a relationship between PTVvolume and dose parameters?
My SBRT Experience Is there a relationship between totallung volume and dose parameters?
My SBRT Experience Is there a relationship between totallung volume and dose parameters?
Does SBRT Work? 5 months post treatment
Does SBRT Work? 17 months post treatment
Does SBRT Work? 31 months post treatment
Conclusions? SBRT planning is not for the faint ofheart Plan quality seems to be largely afactor of the protocol constraints There “appears” to be a relationshipbetween PTV volume and some planparameters It appears to be more difficult to achievethe V50%, Lung V20 and Lung V7parameter as PTV volume increases
Advice Read the protocols – but sometimesthey have English bad Make sure you’re using the rightprescription dose / OAR parameters forthe clinical situation Do a site visit Don’t get too freaked out about SBRTplanning But don’t take it lightly
Thanks Rachel HackettAndrew GorajJeremy GarvinRichard RussoAnurag SinghJorge Gomez
Thanks Callum Hales
Stereotaxy the superposition of a 3D co-ordinate system upon a given organ or structure. Requires an external frame, fixed to the . As of Sept 1 2016 – 536 cases. Lung SBRT Experience Lung SBRT (approx. 90% of cases) Follow RTOG protocols . Spinal Cord Max 18 Gy
