Radiotherapy

Question 1

What is radiotherapy?

Answer 1

It’s a treatment that uses high doses of targeted energy to kill cancer and shrink tumours

Question 2

On average how mow much more radiation is used for therapy vs diagnostic?

Answer 2

3000x

Question 3

Which photon energy do we see in radiotherapy?

Answer 3

Compton scattering
Pair production

Question 4

Which photon energy is sent more in diagnostic X-rays?

Answer 4

Photoelectric effect

Question 5

What’s the benefit of the photoelectric effect on image quality?

Answer 5

Excellent image quality

Question 6

Whats Compton scatters effect on the Image?

Answer 6

interaction a electron density

Question 7

what dose does skin radiotherapy use?

Answer 7

70-300 kv

Question 8

What are the components of a radiotherapy machine?

Answer 8

Diagnostic x-ray tube
radiation beam defining system
simulator couch
Image intensifier and xray film holder
rotating gantry

Question 9

What is the treatment planning process?

Answer 9

1. patient referral
2. decision to treat
3. immobilisation
4. planning CT
5. Contour + organ at risk (OAR)
6. create a Radiotherapy plan
7. Checks and QC
8. Image verification
9. Delivery

Question 10

How is cone beam CT used in RT?

Answer 10

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

Question 11

What are some of the common artefacts from Cone beam CT?

Answer 11

beam hardening
undersampling
inhomogeneity
cone - beam effect
patient motion
metal artefact

Question 12

What is the new advancement in the treatment of cancers?

Answer 12

proton radiotherapy - proton beam instead of radiation

Question 13

why do they use 2D imaging in RT?

Answer 13

• 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

Question 14

Do they use KV or MV for RT?

Answer 14

MV - megavolts

Question 15

Why do they use 3D / Cone beam CT in RT?

Answer 15

+ 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

Question 16

How do they use 4DCT / Deep inspiration breath-hold in RT?

Answer 16

• 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

Question 17

What does SABR stand for?

Answer 17

Stereotactic ablative radio therapy