Gamma Knife

Question 1

What is the half life of cobalt 60?

Answer 1

5.26 years

Source changed every 5 years

Question 2

What does the gamma knife unit include?

Answer 2

Consists of the patient positioning unit 
And the Radiation unit. 
- Collimator system 
- Cobalt 60 sources 
- Shielding around source 
- and shielding doors

Question 3

What are the treatment day steps for Gamma knife?

Answer 3

Patient arrival 
Frame attachment 
Planning CT
Planning MRI
Treatment Plan 
Quality Assurance Checks 
Treatment (30 min - 2hr)
Frame Removal 
Discharge

Question 4

What is the gamma knife imaging process and why doe we use a frame?

Answer 4

• frame provides spatial references & immobilizes the patient’s head
• Patient scanned with an Indicator box in place - locating pins and must fit perfectly
• Reference fiducials during image acquisition
• Creates the Stereotactic space for each image
• Images sent directly to Gamma Plan via dicom

Question 5

Define the terms gradient and conformity

Answer 5

Conformity: describes how well radiation dose conforms to the target volume

Gradient: Describes how well normal tissue is spared (steep dose drop off)

Question 6

Define the terms gamma angle and shot

Answer 6

shot - each isocenter/ patient position

gamma angle - tilt of patients head (70 ,90, 110). Each angle = 1 run. One room entry per run.

Question 7

What is the therapeutic window

Answer 7

The gap between tumour kill and complication of normal tissue

Question 8

Compare radiosurgery vs radiotherapy

Answer 8

Single high dose of radiation (12-150Gy) vs Multiple small doses of radiation
Tissue ablation/ destruction vs Mitotic cell death (DNA damage) in dividing cells
Requires defined target vs. often used with margins to treat lesions
Typically for targets less than 3-4cm vs. can be used for large volumes