emerging image guided and adaptive RT technologies

Question 1

what is Image guidance

Answer 1

involves use of any imaging to aid decision making
main decision in RT is whether to treat and how/when to treat

Question 2

rationale for IGRT

Answer 2

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

Question 3

Treatment technologies

Answer 3

conventional LINAC
Tomo
halcyon
VERO SBRT
Cyberknife
MRL
Proton therapy

Question 4

IGRT technologies

Answer 4

planar - 2D
Volumetric -3D and 4D
Ionising
non-ionising

Question 5

conventional LINAC

Answer 5

3DCRT, IMRT, VMAT, SBRT delivery
Planar MV
Planar KV

Question 6

Planar kV vs MV imaging

Answer 6

pros: better resolution and contrast than MV
Lower imaging dose
Requires additional LINAC Hardware
Similar workflow to traditional MV methods
widely available and utilised

Question 7

Fiducial markers

Answer 7

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

Question 8

Fiducial markers Strengths

Answer 8

FMs surrogate of prostate motion
very fast method of localisation
staff have great confidence when aligning FMs
very low intra-and inter observer variability

Question 9

fiducial markers weakness

Answer 9

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

Question 10

volumetric MVCBCT

Answer 10

use the treatment beam and EPID to acquire CBCT
Low contrast - high energy
good for artefacts
same isocentre of imaging and treatment

Question 11

kVCBCT imaging

Answer 11

orthogonal to MV source
kV source
flat panel detector

Question 12

full-fan versus half-fan

Answer 12

full fan: head due to narrow FOV
half fan: chest/prostate, takes longer than full fan

Both reduces beam hardening effect and scatter

Question 13

when to replan

Answer 13

disease progression
disease response
weight loss

Question 14

varian ETHOS

Answer 14

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

Question 15

cyberknife technology

Answer 15

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

Question 16

Exactrac stereoscopic kV imaging

Answer 16

two floor-mounted kV sources
two ceiling-mounted aSi detectors
available as add-on for Varian, Elekta and Siemens Linacs
Allows frameless radiosurgery

Question 17

VERO SBRT technology

Answer 17

ring gantry similar to tomotherapy
MV source
Stereoscopic kV imaging
unrestrcited imaging

Question 18

CT on rails

Answer 18

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

Question 19

Limit CT on rails

Answer 19

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

Question 20

Helical TomoTherapy (HT) Imaging

Answer 20

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

Question 21

MR linac

Answer 21

MRIdian system
MRIdian Linac system
Elekta Unity

Question 22

Challenges in development phases for MRL

Answer 22

RF interference between linac and magnetic field
affects: radiation dose distribution and MR iamge quality
increased imaging complexity
Education for RO/RT staff

Question 23

non-ionising technologies

Answer 23

Calypso system
3D ultrasound
Optical surface imaging

Question 24

Calypso 4D localisation system

Answer 24

limited to implanted markers
continuous, real time monitoring of the prostate

Question 25

Calypso workflow

Answer 25

1. transponders permanently implanted 2. electromagnetic array is positioned above the treatment site. array sends signal that excites the transponders, which communicate the location of the target 3. System detects tumour movement in real time and if required, the RT can pause treatment to make adjustments 4. Varian Calypso system links with our linear accelerator which produces and delivers

Question 26

advantages of Calypso

Answer 26

rapid, high dose rate treatment is always on target Setup and delivery times are decreased Reduced treatment margins Reduced GI, GU and sexual complications

Question 27

Ultrasound Guided technologies

Answer 27

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

Question 28

3D US

Answer 28

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

Question 29

SGRT

Answer 29

Rapidly growing technique which uses stereo vision technology to track patients surface in 3D, for both setup and motion management during radiotherapy

Question 30

SGRT applications

Answer 30

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

Question 31

SGRT workflow

Answer 31

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

Question 32

Disadvantage of SGRT

Answer 32

no information on internal motion

Question 33

Varian RPM

Answer 33

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

Question 34

Disadvantages of Calypso

Answer 34

More invasive as seeds are required

Question 35

Clarity

Answer 35

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

Question 36

Clarity technology

Answer 36

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

Question 37

BAT

Answer 37

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