Clinical Clinical Implementation of Implementation of Respiratory GatingRespiratory Gating

Kerry Kerry HibbittsHibbitts, MS, DABR, MS, DABRThe University of Oklahoma Medical CenterThe University of Oklahoma Medical Center

Presentation OutlinePresentation Outline

Problems arising from respiratory motionProblems arising from respiratory motion

Some methods to account for respiratory motionSome methods to account for respiratory motion

Varian RealVarian Real--Time Position Management (RPM) Time Position Management (RPM) implementationimplementation

Future techniquesFuture techniques

Problems Arising From Problems Arising From Respiratory MotionRespiratory Motion

Image acquisition limitationsImage acquisition limitations

Treatment planning limitationsTreatment planning limitations

Radiation delivery limitationsRadiation delivery limitations

Image Acquisition LimitationsImage Acquisition Limitations

Motion artifacts result if respiratory motion not Motion artifacts result if respiratory motion not accounted foraccounted for

This can result in target/normal tissue delineation errorsThis can result in target/normal tissue delineation errors

Image Acquisition LimitationsImage Acquisition Limitations

Treatment Planning LimitationsTreatment Planning Limitations

Larger margins have to be used when creating PTV from Larger margins have to be used when creating PTV from CTVCTV

Increased margins mean greater volumes of healthy Increased margins mean greater volumes of healthy tissue treatedtissue treated

Radiation Delivery LimitationsRadiation Delivery Limitations

IntrafractionIntrafraction motion produces averaging/blurring of dose motion produces averaging/blurring of dose distribution over path of motiondistribution over path of motion

InterfractionInterfraction motion produces shift of dose distributionmotion produces shift of dose distribution

Overall effect is blurring of the dose distribution near the Overall effect is blurring of the dose distribution near the beam edgesbeam edges

Methods to Account for Methods to Account for Respiratory MotionRespiratory Motion

Motion encompassing methodsMotion encompassing methods

Respiratory gating methodsRespiratory gating methods

Breath hold methodsBreath hold methods

Forced shallow breathing with abdominal compressionForced shallow breathing with abdominal compression

RealReal--time tumor trackingtime tumor tracking

Motion Encompassing MethodsMotion Encompassing Methods

Slow CT scanningSlow CT scanning

Inhalation and exhalation breathInhalation and exhalation breath--hold CThold CT

Slow CT ScanningSlow CT Scanning

CT scanner operated very slowly so that multiple CT scanner operated very slowly so that multiple respiration phases are recorded per slicerespiration phases are recorded per slice

Resulting tumor image should encompass full extent of Resulting tumor image should encompass full extent of respiratory motionrespiratory motion

Slow scanning geometry more representative of entire Slow scanning geometry more representative of entire respiratory cycle that will occur during treatmentrespiratory cycle that will occur during treatment

Loss of resolution due to motion blurring (larger errors in Loss of resolution due to motion blurring (larger errors in tumor and normal tissue delineation)tumor and normal tissue delineation)

Inhalation and Exhalation Inhalation and Exhalation BreathBreath--hold CThold CT

Acquire both inhalation and exhalation breath hold CT Acquire both inhalation and exhalation breath hold CT scansscans

To reduce CT time, acquire free breathing full scan, with To reduce CT time, acquire free breathing full scan, with inhalation and exhalation scans through tumor volume inhalation and exhalation scans through tumor volume onlyonly

Fuse images for contouringFuse images for contouring

Respiratory Gating MethodsRespiratory Gating Methods

CT scans are acquired and correlated with a concurrently CT scans are acquired and correlated with a concurrently acquired respiratory motion fileacquired respiratory motion file

CT slices obtained can be sorted based on spatial (axial) CT slices obtained can be sorted based on spatial (axial) and temporal (breathing phase) locationand temporal (breathing phase) location

CT sets can be reconstructed for any portion of the CT sets can be reconstructed for any portion of the respiratory cyclerespiratory cycle

Variations in respiratory pattern during acquisition can Variations in respiratory pattern during acquisition can affect images, breath training techniques can helpaffect images, breath training techniques can help

Respiratory Gating MethodsRespiratory Gating Methods

Gating using external markersGating using external markers

External markers placed on patientExternal markers placed on patient’’s surface used to monitor s surface used to monitor patientpatient’’s respiratory motions respiratory motion

Markers are commonly IR reflective devices used in conjunction Markers are commonly IR reflective devices used in conjunction with an infrared camera with an infrared camera

Gating using internal markersGating using internal markers

Internal markers implanted in or near tumor used to monitor Internal markers implanted in or near tumor used to monitor patientpatient’’s respiratory motions respiratory motion

Commonly gold seeds, which must then be imaged with Commonly gold seeds, which must then be imaged with stereotactic kV imaging systemstereotactic kV imaging system

Breath Hold MethodsBreath Hold Methods

DeepDeep--inspiration breath holdinspiration breath hold

ActiveActive--breathing controlbreathing control

DeepDeep--Inspiration Breath HoldInspiration Breath Hold

Patient is trained to reproduce a deep inhalation breath Patient is trained to reproduce a deep inhalation breath hold during simulation and treatmenthold during simulation and treatment

Volume of air inhaled by patient monitored by Volume of air inhaled by patient monitored by spirometerspirometer

Highly reproducible results possibleHighly reproducible results possible

ActiveActive--Breathing ControlBreathing Control

Technique for suspending breathing at any Technique for suspending breathing at any predetermined position (usually moderate or deep predetermined position (usually moderate or deep inhalation)inhalation)

Monitoring apparatus consists of Monitoring apparatus consists of spirometerspirometer connected connected to balloon valveto balloon valve

After a predefined volume of air (threshold volume) has After a predefined volume of air (threshold volume) has passed through the passed through the spirometerspirometer, a small balloon valve , a small balloon valve inflates and occludes the tube, applying an assisted inflates and occludes the tube, applying an assisted breath hold for a predefined period of timebreath hold for a predefined period of time

Forced Shallow Breathing/Forced Shallow Breathing/ Abdominal CompressionAbdominal Compression

Utilizes stereotactic body frame with attached plate or Utilizes stereotactic body frame with attached plate or respiratory belt that presses against abdomen to reduce respiratory belt that presses against abdomen to reduce diaphragm motion and encourage shallow breathingdiaphragm motion and encourage shallow breathing

RealReal--time Tumor Trackingtime Tumor Tracking

Goal is to reposition beam dynamically to follow tumor Goal is to reposition beam dynamically to follow tumor motion during treatmentmotion during treatment

To accomplish this, the system must be able toTo accomplish this, the system must be able to

Detect tumor position in real timeDetect tumor position in real time

Compensate for time delays in beamCompensate for time delays in beam--positioning positioning responseresponse

Reposition the beamReposition the beam

Adapt the Adapt the dosimetrydosimetry to allow for these changesto allow for these changes

History of RespiratoryHistory of Respiratory Management atManagement at

OU Medical CenterOU Medical Center

NonNon--Gated SolutionGated Solution

Acquire three separate series of scans :Acquire three separate series of scans :

Regular breathingRegular breathing

Full inhalationFull inhalation

Full exhalationFull exhalation

The three sets of images are fused in the planning The three sets of images are fused in the planning system, with the CTV contoured in each seriessystem, with the CTV contoured in each series

A composite CTV can then be contoured which A composite CTV can then be contoured which encompasses the extremes of motion of the CTV during encompasses the extremes of motion of the CTV during the breathing cyclethe breathing cycle

ExampleExample

Regular breathing series merged with inhalation seriesRegular breathing series merged with inhalation series

ExampleExample

Regular breathing series merged with exhalation seriesRegular breathing series merged with exhalation series

ExampleExample

ITV drawn based on motion in all seriesITV drawn based on motion in all series

Gated SolutionGated Solution

A respiratory gating system (Varian RealA respiratory gating system (Varian Real--time Positiontime PositionManagement) is used to correlate the time of theManagement) is used to correlate the time of theacquisition of an image with a breathing signal it detectsacquisition of an image with a breathing signal it detects

BreathingBreathing--synchronized acquisition of these imagessynchronized acquisition of these imagesensures that the images used for planning correspond toensures that the images used for planning correspond toa known breathing state that can be detected duringa known breathing state that can be detected duringtreatment, enabling beamtreatment, enabling beam--on only when the patient is inon only when the patient is inthat respiratory statethat respiratory state

Two Approaches to Image Two Approaches to Image AcquisitionAcquisition

ProspectiveProspective

Images are acquired only during a portion of the Images are acquired only during a portion of the respiration cyclerespiration cycle

RetrospectiveRetrospective

Images are acquired during the entire respiration cycle Images are acquired during the entire respiration cycle and sorted laterand sorted later

ProspectiveProspective

RetrospectiveRetrospective

Two Gating MethodsTwo Gating Methods

Amplitude gatingAmplitude gating

The gated range is defined by upper and lower The gated range is defined by upper and lower thresholdsthresholds

Phase gatingPhase gating

The gated range is defined by two points of the The gated range is defined by two points of the breathing cyclebreathing cycle

Amplitude GatingAmplitude Gating

Phase GatingPhase Gating

Gating System ComponentsGating System Components

Infrared camera with infrared light sourcesInfrared camera with infrared light sources

External reflective markersExternal reflective markers

GE Discovery CT scannerGE Discovery CT scanner

GE 4D SoftwareGE 4D Software

RPM switchboxRPM switchbox

RPM workstationRPM workstation

Acquiring ScanAcquiring Scan

The patient is placed in treatment position in the CT The patient is placed in treatment position in the CT roomroom

A reflective marker box is taped to the chest and itA reflective marker box is taped to the chest and it’’s s position is marked for reproduction during treatmentposition is marked for reproduction during treatment

Acquiring ScanAcquiring Scan

The camera is adjusted so that the reflective markers The camera is adjusted so that the reflective markers are visible on the monitorare visible on the monitor

Acquiring ScanAcquiring Scan

The patient is coached to breathe normallyThe patient is coached to breathe normally

Once a regular breathing pattern is established, the CT Once a regular breathing pattern is established, the CT scan is acquired and exported to the 4D workstationscan is acquired and exported to the 4D workstation

Preparing Scan For PlanningPreparing Scan For Planning

The 4D workstation uses the patientThe 4D workstation uses the patient’’s respiratory file to s respiratory file to sort the series images into one of ten segments of the sort the series images into one of ten segments of the breathing cyclebreathing cycle

Preparing Scan For PlanningPreparing Scan For Planning

Once the images are sorted, the position of the tumor is Once the images are sorted, the position of the tumor is noted in each of the ten phases, and those phases that noted in each of the ten phases, and those phases that exhibit minimal motion are chosen for treatment exhibit minimal motion are chosen for treatment planningplanning

Preparing Scan For PlanningPreparing Scan For Planning

A new CT series is created based on these phases and is A new CT series is created based on these phases and is exported to the treatment planning systemexported to the treatment planning system

Preparing Scan For PlanningPreparing Scan For Planning

To confirm the proper choice of phases for gating, a movie mode is available in the 4D software for observing tumor motion

Treatment PlanningTreatment Planning

•• Once the gated CT series is created, the physician Once the gated CT series is created, the physician delineates the ITVdelineates the ITV

•• The The dosimetristdosimetrist creates the PTV by adding a 7mm creates the PTV by adding a 7mm margin to the ITVmargin to the ITV

•• The CT series and associated contours are then exported The CT series and associated contours are then exported to planning system, where planning proceeds as usualto planning system, where planning proceeds as usual

Treatment DeliveryTreatment Delivery

The patient is repositioned on the treatment couch per The patient is repositioned on the treatment couch per CT simulation and planningCT simulation and planning

A reflective marker box is repositioned on the chest per A reflective marker box is repositioned on the chest per CT simulation and planningCT simulation and planning

The camera response is adjusted until the markers are The camera response is adjusted until the markers are just visible in the monitorjust visible in the monitor

The patient is coached in previously established The patient is coached in previously established breathing techniquebreathing technique

At the treatment console, the RPM gating switch is At the treatment console, the RPM gating switch is turned on and respiratory tracking is begunturned on and respiratory tracking is begun

Treatment DeliveryTreatment Delivery

Treatment DeliveryTreatment Delivery

Once a regular breathing pattern is established, the Once a regular breathing pattern is established, the phase limits for gating established during treatment phase limits for gating established during treatment planning are selectedplanning are selected

Treatment DeliveryTreatment Delivery

Once respiratory motion recording has begun, treatment Once respiratory motion recording has begun, treatment delivery is enabled, with radiation being delivered only delivery is enabled, with radiation being delivered only during those portions of the breathing cycle which were during those portions of the breathing cycle which were established during planningestablished during planning

Treatment DeliveryTreatment Delivery

When treatment is completed, the breathing pattern When treatment is completed, the breathing pattern used for treatment is saved to the databaseused for treatment is saved to the database

Quality AssuranceQuality Assurance

A breathing phantom in conjunction with the marker A breathing phantom in conjunction with the marker block is used to test the RPM systemblock is used to test the RPM system’’s tracking ability in s tracking ability in both the CT room and the treatment room daily prior to both the CT room and the treatment room daily prior to any respiratory gating procedureany respiratory gating procedure

Quality AssuranceQuality Assurance

Quality AssuranceQuality Assurance

An IMRT dose verification phantom (Standard Imaging) An IMRT dose verification phantom (Standard Imaging) in conjunction with a respiratory gating platform is used in conjunction with a respiratory gating platform is used monthly to verify the RPM systemmonthly to verify the RPM system’’s gating capability in s gating capability in both the CT room and the treatment roomboth the CT room and the treatment room

Quality AssuranceQuality Assurance

Quality AssuranceQuality Assurance

Future TechniquesFuture Techniques

Recently have begun using forced shallow breathing with Recently have begun using forced shallow breathing with abdominal compressionabdominal compression

Future TechniquesFuture Techniques

Future TechniquesFuture Techniques

Recent commission of Recent commission of ExacTracExacTrac with possibility of realwith possibility of real-- time tumor trackingtime tumor tracking

Future TechniquesFuture Techniques

Thank You!Thank You!