SABR motion management Flashcards
What sites can SABR be used for?
Oligometastases - intermediate spread of cancer between local disease and widespread mets Lung Liver Adrenal Spine Pelvic nodes
What immobilisation is available for lung SABR?
Wingboards
Vac-bags
Thoraxsupport
How should the immobilisation of choice be decided?
Compare set up errors of the systems using IGRT
What planning CT techniques should be used?
4D CT
Slow CT
kV fluoro
How does the Varian RPM 4D respiratory measuring system work?
Light weight, small marker - single region surrogate of breathing motion
IR light/camera system
6 IR reflective markers - on block placed on patient’s sternum
Tracks block to create waveform of breathing
How does the ANZAI 4D respiratory measuring system work?
Pressure sensor in elastic belt around diagphram
Change in pressure = waveform
How does the CDRAD catalyst 4D respiratory measuring system work?
Optical surface scanning without markers or fiducials
Can be used to assist patient posture correction
How does the VISIONRT gatert/gatect 4D respiratory measuring system work?
3D surface mapping - no markers or fiducials
Can be used to assist patient posture correction
How does the Calypso 4D respiratory measuring system work?
Implanted EM transponders
Use EM array detector
Not a motion surrogate and invasive
What are the issues with normal CT, 4DCT and breath hold for locating the tumour?
Normal CT - tumour caught at arbitrary snapshots
4DCT - Image artefacts due to motion
Breath hold - most accurate tumour shape but at an extreme position
How does the retrospective gating on Siemens CTs work?
Slow CT scan with a pitch of 0.1
Thorax is imaged with overlapping spirals
Each part imaged for 10 tube rotations
Each rotation takes 0.5s - each part of patient is imaged for whole breathing cycle
What are the disadvantages of retrospective gating?
Imaging dose ~3x 4D scan
Automatic dose control not available for 4D acquisitions
Scan length limitations
Imaging anatomy outside CT’s normal FoV not possible
What binning methods are used?
Amplitude binning - fewer image artefacts
Phase binning - better for reconstruction of peaks, contains image artefacts
Bin size independent of number of bins
What are the uncertainties in retrospective gating?
Single movie representation - is it representative of breathing cycle? Has the surrogate modified the breathing behaviour?
What is prospective gating?
CT only gathered during defined interval of breathing cycle
