Radiotherapy Flashcards
What is radiotherapy?
It’s a treatment that uses high doses of targeted energy to kill cancer and shrink tumours
On average how mow much more radiation is used for therapy vs diagnostic?
3000x
Which photon energy do we see in radiotherapy?
Compton scattering
Pair production
Which photon energy is sent more in diagnostic X-rays?
Photoelectric effect
What’s the benefit of the photoelectric effect on image quality?
Excellent image quality
Whats Compton scatters effect on the Image?
interaction a electron density
what dose does skin radiotherapy use?
70-300 kv
What are the components of a radiotherapy machine?
Diagnostic x-ray tube
radiation beam defining system
simulator couch
Image intensifier and xray film holder
rotating gantry
What is the treatment planning process?
- patient referral
- decision to treat
- immobilisation
- planning CT
- Contour + organ at risk (OAR)
- create a Radiotherapy plan
- Checks and QC
- Image verification
- Delivery
How is cone beam CT used in RT?
Fan beam irradiates panel
200* or 360* rotation in 38-60 sec
reconstruction of data into 3D image matrix
Artefacts due to TIME and ARC
What are some of the common artefacts from Cone beam CT?
beam hardening
undersampling
inhomogeneity
cone - beam effect
patient motion
metal artefact
What is the new advancement in the treatment of cancers?
proton radiotherapy - proton beam instead of radiation
why do they use 2D imaging in RT?
- To verify the position of the RT beams
- Use bones for matching
- Can see the outline of the patients’ skin on MV
- Limited for internal soft tissue
- Useful for sites relying on bony anatomy
eg brain, spine, head, neck and limbs - can visualise some surgical clips
Do they use KV or MV for RT?
MV - megavolts
Why do they use 3D / Cone beam CT in RT?
+ volumetric imaging
+ allows matching to soft tissue structures
+ used daily for lung, prostate, cervix, bladder, rectum, larynx and oesophagus
+ used once a week for other sites to pick up changes in tumour size, patient size and to verify that a bony match approach is acceptable
How do they use 4DCT / Deep inspiration breath-hold in RT?
- advanced techniques used for sites where breathing motion impacts the margin required for treatment
- 4DCT for lungs/ SABR lung patients scans and bins the data into 10 phases of breathing cycle which allows the movement of the tumour to be mapped.
- DIBH - reduced moment as scan and treat in breath-hold. used for breast, lung, mediastinum.
- smaller target - less dose to normal tissue - reduced side effects
- possibility to escalate dose to targets
What does SABR stand for?
Stereotactic ablative radio therapy
