Tomotherapy

Question 1

What is it?

Answer 1

-standard LINAC w a wave guide
-magnetron producing radiofrequency which ↑ en of e
-6 MV (3.5MV for imaging)
-FFF but includes a beam hardener (↓ flux of low intensity photons)

Question 2

What is different (1)

Answer 2

The Linac is mounted on a CT “ring” gantry
-slip ring allow gantry to rotate continously

Question 3

What is different (2)

Answer 3

• MLC pneumatically driven
• very fast
• Binary leaf state

Question 4

What is different (3)

Answer 4

-The Beam stop is on the gantry:
– Acts as a counterweight to allow free travel on the gantry
– Absorbs photons

Question 5

What is different (4)

Answer 5

*Target to axis distance = 85 cm (not 100cm)
*51 Arc segments instead of e.g. 8 fields
*True CT image (although it is MV)

Question 6

Major differences

Answer 6

• No collimator rotation and wedges
• No couch accessories/couch rotation
• No flattening filter
• No field matching

Question 7

Radixact

Answer 7

-Upgraded system
* Tomotherapy unit
* kV CT and MVCT inbuilt

Question 8

Radixact:
-kV for
-mV for

Answer 8

-soft tissue matching, HU values, Adaptive planning
-metallic objects

Question 9

beam harder allows

Answer 9

the beam to become harder bc average en. of photons increase

Question 10

why do we want to get rid of low en photons

Answer 10

bc photons wont penetrate far and tend to get picked up at skin surface

Question 11

tomotherapy uses

Answer 11

fan beamCT MV

Question 12

problems with MVCT

Answer 12

-produces large dose w lower quality image
-lack of contrast between bone and soft tissue

Question 13

benefits with MVCT

Answer 13

metallic objects will image better