Image fusion

Question 1

Why fuse images?

Answer 1

Optimisation of the target volume delineation. We want a tighter margin around the volume to escalate dose.

Question 2

What is the difference between image fusion and registration?

Answer 2

With fusion the two images are fused to create one. With registration the images are overlaid - there are still 2 images and a co-ordinate system monitors the movements between the two. Registration is the first step of fusion.

Question 3

What are the 2 types of fusion?

Answer 3

Hardware and software.
Hardware = a hybrid machine that is capable of taking 2 types of images
Software = 2 separate machines and fuse online.

Question 4

What are the advantages of PET-CT?

Answer 4

Reduced inter-observer variation in GTV delineation
Reduces size of GTV
Good for looking at nodes so can identify nodes missed by CT or MRI - this can lead to changing the stage and intent of treatment
Identify parts of the GTV potentially requiring additional dose
Superior sensitivity in cases of lymph nodes, mets, monitoring following treatment

Question 5

What are the advantages of MRI-CT?

Answer 5

Gives better soft tissue detail with bony anatomy and spatial resolution
Reduced inter-observer variability
Smaller target volumes

Question 6

What are the disadvantages of PET-CT?

Answer 6

Limited spatial resolution
Lack of standardised method for signal segmentation
False positive PET readings due to inflammation

Question 7

What are the advantages of fusion?

Answer 7

Precise imaging for target delineation
Inclusion of all soft tissue spread - spread that cannot be seen on CT images
Minimising OAR volume included in PTV
Precision on PTV which can lead to dose escalation