emerging image guided and adaptive RT technologies Flashcards
what is Image guidance
involves use of any imaging to aid decision making
main decision in RT is whether to treat and how/when to treat
rationale for IGRT
increase precision and accuracy in RT
reduced toxicity with the potential for dose escalation and improved tumour control
conformity
dose escalation
reduce inter and intra fraction errors
Treatment technologies
conventional LINAC
Tomo
halcyon
VERO SBRT
Cyberknife
MRL
Proton therapy
IGRT technologies
planar - 2D
Volumetric -3D and 4D
Ionising
non-ionising
conventional LINAC
3DCRT, IMRT, VMAT, SBRT delivery
Planar MV
Planar KV
Planar kV vs MV imaging
pros: better resolution and contrast than MV
Lower imaging dose
Requires additional LINAC Hardware
Similar workflow to traditional MV methods
widely available and utilised
Fiducial markers
routinely used for prostate irradiation
small gold seeds
surrogate for prostate match to fiducials to overcome factor such as: bladder filling, rectal filling and patient motion
Fiducial markers Strengths
FMs surrogate of prostate motion
very fast method of localisation
staff have great confidence when aligning FMs
very low intra-and inter observer variability
fiducial markers weakness
associated expense
invasive procedure
some patients ineligible
rely on few discrete points to localise the prostate
evaluation of nearby organs and deformation of the target is difficult
volumetric MVCBCT
use the treatment beam and EPID to acquire CBCT
Low contrast - high energy
good for artefacts
same isocentre of imaging and treatment
kVCBCT imaging
orthogonal to MV source
kV source
flat panel detector
full-fan versus half-fan
full fan: head due to narrow FOV
half fan: chest/prostate, takes longer than full fan
Both reduces beam hardening effect and scatter
when to replan
disease progression
disease response
weight loss
varian ETHOS
ETHOS therapy
FDA approval
uses AI and ML to create contours and generate adapted plans for physician review within minutes, while a patient is on the treatment couch
cyberknife technology
two ceiling-mounted kV sources
two floor-mounted aSi detectors
process:
1. fiducial placement
2. setup and imaging
3. planning
4. treatment and follow up
Exactrac stereoscopic kV imaging
two floor-mounted kV sources
two ceiling-mounted aSi detectors
available as add-on for Varian, Elekta and Siemens Linacs
Allows frameless radiosurgery
VERO SBRT technology
ring gantry similar to tomotherapy
MV source
Stereoscopic kV imaging
unrestrcited imaging
CT on rails
Patient setup on CT couch (BBs placed on reference marks)
CT scan performed
table rotated 180 degrees
patient positioned at treatment isocentre
Diagnostic quality CT reviewed
table position adjusted
Limit CT on rails
considerable differences between in room CT and EPI exist
Couch sag that occurs at the CT on rails gantry could not be totally corrected for
other confounding factors are:
- action of rotating the couch
- associated time lag between image acquisitions
- EPI image quality and outlining uncertainties
Helical TomoTherapy (HT) Imaging
MV beam source placed on a ring gantry
MV fan beam - CT
provides less sot tissue contrast than kV CT but less artefacts from high Z material
MR linac
MRIdian system
MRIdian Linac system
Elekta Unity
Challenges in development phases for MRL
RF interference between linac and magnetic field
affects: radiation dose distribution and MR iamge quality
increased imaging complexity
Education for RO/RT staff
non-ionising technologies
Calypso system
3D ultrasound
Optical surface imaging
Calypso 4D localisation system
limited to implanted markers
continuous, real time monitoring of the prostate
Calypso workflow
- transponders permanently implanted
- electromagnetic array is positioned above the treatment site. array sends signal that excites the transponders, which communicate the location of the target
- System detects tumour movement in real time and if required, the RT can pause treatment to make adjustments
- Varian Calypso system links with our linear accelerator which produces and delivers
advantages of Calypso
rapid, high dose rate treatment is always on target
Setup and delivery times are decreased
Reduced treatment margins
Reduced GI, GU and sexual complications
Ultrasound Guided technologies
not as common as other imaging modalities
previous system suffered from significant systematic errors –> inaccurate treatment localisation –> US probe
traditional 2D - hard to interpret, operator dependent
strong motivation to have inexpensive, non-IR, real-time guidance method but confidence needs to be restored
3D US
verify target position without ionising radiation
marketed for breast and prostate
can be used to monitor target over time
also used for patient alignment in the treatment room
Clarity and BAT system
SGRT
Rapidly growing technique which uses stereo vision technology to track patients surface in 3D, for both setup and motion management during radiotherapy
SGRT applications
setup: SGRT helps speed up and improve the accuracy of setup
treatment: SGRT can reduce the need for immobilisation while helping to ensure the patient is in the correct position for treatment in all 6 degrees of freedom
4DCT: SGRT enables contactless, non-invasive reconstruction of 4DCT data
SGRT workflow
reference surface model: acquiring a 3D surface with alignRT at simulation
At each treatment fraction, the system images the current patient position
this image is registered to the reference surface
couch shifts then calculated to correct inconsistencies between actual and planned positions.
will alert RTs of gross movement
Disadvantage of SGRT
no information on internal motion
Varian RPM
Non-invasive, video based system
uses an infrared tracking camera and a reflective marker array
measures the patient’s respiratory pattern and range of motion, displays as a waveform
reflectors act as surrogate for patient’s respiratory cycle
Disadvantages of Calypso
More invasive as seeds are required
Clarity
Ultrasound system using TRUS or TPUS
More commonly used TPUS for continual matching
Can be applied in both simulation and treatment
Can be used for patient aligament in the treatment room
Can verify the target position without additional ionising radiation
Provides real time monitoring of prostate
Clarity technology
ultrasound probe is calibrated to the same
isocentre as the CT system
• series of reflective markers used to track its
position in space
• enables the volumetric ultrasound image to be
automatically fused with the planning CT
• providing additional information for contouring
• no extra appointment is needed
BAT
Can be used for patient alignment in the treatment room
Can verify the target position without additional ionising radiation
Provides real-time monitoring of the target
Requires only 90 seconds for scanning and repositioning
