Principles and Practice of Radiation Therapy Chapter 23 Computed Tomography Simulation Copyright ©...

Principles and Practice of Principles and Practice of Radiation TherapyRadiation Therapy

Chapter 23Chapter 23

Computed Tomography Computed Tomography SimulationSimulation

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.Copyright © 2010 by Mosby, Inc., an affiliate of Elsevier Inc. 22

Historical FactsHistorical Facts

Godfrey HounsfieldGodfrey Hounsfield First computed tomography (CT) unit First computed tomography (CT) unit

Alan Cormack Alan Cormack Developed math calculations or algorithmsDeveloped math calculations or algorithms

Shared the 1979 Nobel PrizeShared the 1979 Nobel Prize


General InformationGeneral Information

CT simulator specific for therapyCT simulator specific for therapy High-performance scannerHigh-performance scanner Laser and patient marking systemLaser and patient marking system Virtual simulationVirtual simulation


Principles of OperationPrinciples of Operation

Gantry external controlsGantry external controls Couch controlsCouch controls Gantry tiltGantry tilt Emergency off buttonsEmergency off buttons Localizer lasersLocalizer lasers


Principles of OperationPrinciples of Operation

Gantry internal Gantry internal controlscontrols Detector arrayDetector array X-ray tubeX-ray tube


Hounsfield UnitsHounsfield Units

Shades of grayShades of gray Electron density of Electron density of

tissuetissue


Benefits of CT SimulationBenefits of CT Simulation

Outline critical structuresOutline critical structures Delineate target volumeDelineate target volume Achieve optimal beam placementAchieve optimal beam placement Boost fields planned without patient present Boost fields planned without patient present


Benefits of CT SimulationBenefits of CT Simulation

Beam’s eye viewBeam’s eye view Electronic field shapingElectronic field shaping Construction of digital reconstructed Construction of digital reconstructed

radiographs (DRRs)radiographs (DRRs) Calculation of dose distributionCalculation of dose distribution


Considerations and Limitations of Considerations and Limitations of CT SimulationCT Simulation

Bore sizeBore size Width and shape of couchWidth and shape of couch Laser systemLaser system Acquisition/patient marking timeAcquisition/patient marking time


Considerations and Limitations of Considerations and Limitations of CT SimulationCT Simulation

CT numbers in dose inhomogeneity CT numbers in dose inhomogeneity correctionscorrections

Setup parameters and treatment accessories Setup parameters and treatment accessories unable to be verifiedunable to be verified

Must visualize entire contourMust visualize entire contour


Simulation ProceduresSimulation Procedures

Presimulation planningPresimulation planning Machine limitationsMachine limitations

• ImmobilizationImmobilization

• Patient positioningPatient positioning


Contrast AgentsContrast Agents

Medical historyMedical history Oral Oral IntravenousIntravenous IntrathecalIntrathecal IntraarticularIntraarticular


CT SimulationCT Simulation

Room preparationRoom preparation Explanation of Explanation of

procedureprocedure Patient positioning Patient positioning

and immobilizationand immobilization Data acquisitionData acquisition


CT SimulationCT Simulation

Target and Target and normal tissue normal tissue localizationlocalization

Virtual simulation Virtual simulation of treatment of treatment fieldsfields

Dose distributionDose distribution Documenting Documenting

datadata


Image QualityImage Quality

Spatial Spatial resolutionresolution

Image Image contrastcontrast

NoiseNoise DoseDose ArtifactsArtifacts


CT Image Processing Controls CT Image Processing Controls

Window widthWindow width Window levelWindow level


Quality AssuranceQuality Assurance

AAPM Radiation Therapy Committee Task AAPM Radiation Therapy Committee Task Group No. 66Group No. 66

Daily Warm-up and QADaily Warm-up and QA Monthly QAMonthly QA Yearly QAYearly QA


Image Registration and Correlation Image Registration and Correlation or Fusionor Fusion

Two sets of ImagesTwo sets of Images Scans overlaidScans overlaid


Respiratory GatingRespiratory Gating

Breathing motion Breathing motion artifactsartifacts

Four-dimensional Four-dimensional scanningscanning

SpirometerSpirometer Maximum intensity Maximum intensity

projection (MIP)projection (MIP)

Principles and Practice of Radiation Therapy Chapter 23 Computed Tomography Simulation Copyright ©...

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