Lecture 9 - Image guidance in RT Flashcards
What is IGRT?
Defined as - external beam radiation therapy with positional verification using imaging prior to each fraction
What are types of IGRT?
- 3DCRT
- IMRT
- VMAT
- Radiosurgery
- Stereotastic RT
What is the flow of IGRT?
Original diagnostic images –>
Simulation CT –> (Fused with MRI, PET, SPECT)
DR - Digitally reconstructed radiograph —>
MV and kV
What are other parts of IGRT?
- CBCT
- ultrasound
- transponders
- fiducial markers - seeds
- respiratory gated breathing
What is systematic and random error?
Systematic - deviation that occurs in the same directions, similar magnitude for each fraction throughout treatment
Errors carried forward - happens at CT and planning
Random - deviation that can vary in direction and magnitude during treatment
Errors less likely to be repeated, laser wrong or patient movement
What are the differences in imaging, specifically colorectal cancer?
CT - mostly used, accuracy lower at 45-77%, able to assess nodes and metastases
MRI - higher accuracy 73%, but only 40% sensitivity to lymph node metastases
What is inter and intra factional?
Inter - in between fractions, varies day to day e.g. gas or bladder s
What is motion management?
- the detection and management of exceptional deviations
- gross positioning errors
- weight loss
- e.g. prostate shrinkage during treatment - thats why use seeds
IGRT vs other imaging techniques?
Soft tissue requires higher dose imaging
However high contrast targets such as bone or metalic fiducial markers can be accurately imaged by low dose imaging such as MRI
What is skin render?
- -Representation of the outside of a patient
- can check if the beams match with the skin render prior to imaging
What are transponders?
Magnetic implants 6-7cm long give off a signal to the machine of there location
- used without ionising radiation
- used for both set up and live tracking during treatment
What are anatomical match points?
Points on the image that each day are matched to- at least 3 structures visible within the field to be outlined
- head e.g. clavicle
- prostate e.g. seeds
How much do you contour?
-dependent on your treatment goals
Imaging radical vs palliative?
Palliative - expanded margins therefore expanded tolerances e.g. 1cm
Respiratory gating…
Monitors patient breathing in and out, imaging both sides because 2 isocentres
