Radiotherapy Treatment Verification Flashcards
(8 cards)
What are the benefits of IGRT?
More confidence that the dose is delivered to the right place, minimising the risk of missing the target or irradiating neighbouring tissue/OARs- internal anatomy may change between fraction therefore imaging shows the size and position and shows what/where you will be irradiating.
What is a systematic error?
Error with a consistent magnitude and direction, affecting the mean, consistent in every measurement.
What is a random error?
Error which varies in magnitude and direction, therefore they ‘average out’ over a large enough sample size.
What are some examples of systematic errors in radiotherapy treatment verification?
- Lasers miscalibrated
- Planning CT was an an extreme exhale
- Patient lost weight
- Error in creation or transfer of set up reference images
- kV imaging system not calibrated
What are some examples of random errors in radiotherapy treatment verification?
- Small error in patient position on treatment couch
- Small change in bladder filling
Discuss some of the advantages/disadvantages of Cone Beam Computed Tomography (CBCT) over kV planar imaging.
Advantages
1. Soft tissue visualisation
2. Monitor for tumour growth/shrinkage
3. Monitor patient weight
4. Monitor bladder/rectal filling
Disadvantages
1. Relatively high dose
2. Slow scan time
Give a brief description of the imaging modalities that are typically available on a linear accelerator? What clinical situation would each be used for?
MV images – images show the treatment aperture – imaging and treatment isocentres the same
kV planar images – good bony contrast / fiducial markers
CBCT – soft tissue contrast required / assess flexion
4D CBCT – quantify breathing motion
What are the primary aims of patient immobilisation? Give an example of what is employed for each aim.
Keep the patient in a reproducible position – mask
Keep the patient comfortable - Belly/breast/Wing board / arm rest
