SABR verification

Question 1

What are differences between passive and active motion management techniques?

Answer 1

Passive: accepts motion exists, attempts to quantify range of movement, create the treatment to incorporate the movement prior to delivery
Active: reduce the amount of tumour motion, real-time tracking, adapt treatment throughout delivery

Question 2

What are 3 passive motion management techniques?

Answer 2

Free breathing 4DCT acquisition
ITV delineated over all phases of 4DCT
Free breathing delivery with no motion monitoring

Question 3

What are the 3 active motion management techniques and their advantages and disadvantages?

Answer 3

Compression or breath hold:
Adv - treatment delivery not interrupted
Dis - reproducibility, patient cooperation
Gated delivery:
Adv - minimises breathing motion
Dis - inefficient use of duty cycle, extended beam on time, possibility of postural changes
Tracking:
Adv - beam on throughout
Dis - relies on accurate prediction model and verification during delivery

Question 4

What are the aims and issues with compression devices?

Answer 4

Aim - provide rigid frame of reference that provides repeatable reference position
Issues - Immobilisation and referencing inadequate, IGRT required - not enough as sole method of localisation

Question 5

What treatment imaging can be used?

Answer 5

Stereoscopic 2D kV imaging
3D kVCB
2D kV fluoro
4D kVCB

Question 6

How is passive verification achieved?

Answer 6

3D kVCT to align patient
Use AvIP as reference dataset with ITV as guide
Could do MV portal imaging if using fixed gantry IMRT delivery

Question 7

How is the verification for compression devices achieved?

Answer 7

Same as passive

Need quicker treatment times - VMAT, FFF

Question 8

How is the verification for gating achieved?

Answer 8

kVCBCT to set up bony anatomy and check posture
Compare reference breathing trace with measurement on the day
Acquire fluoro to assess tumour movement
Outline colour linked to gate interval

Question 9

What differences are there between anatomical and 4D CT scans?

Answer 9

4D have fewer frames/sec
Fewer degrees/sec
Longer time

Question 10

What are the standard parameters used in 4D reconstruction?

Answer 10

10 bins

10% width

Question 11

What are he requirements from the SABR guidelines before starting to treat SABR?

Answer 11

Assess immobilisation devices
Assess respiratory compensation
Complete planning studies
Evaluate delivery options
Assess on-line image guidance techniques - available functionality, image quality adequate for purpose

Question 12

How is the ability of imaging systems to measure the tumour motion tested?

Answer 12

Use a breathing phantom with known excursion
Image using 4D
Measure imaged excursion and compare to known excursion