Radiotherapy Equipment

Question 1

What are the features of an x-ray tube?

Answer 1

1. Cathode shield
2. Filament
3. Radiation shield (tungsten)
4. Target
5. Cooling fins
6. Thin glass window
7. Glass envelope

Question 2

What is a cathode shield in an x-ray tube?

Answer 2

Cathode shield is a negatively charged cup that focuses the electron beam

Question 3

What is the filament in an x-ray tube?

Answer 3

Filament is thin metal wire that is heated to release electrons – acts as cathode. Thermionic emission – electrons are boiled off

Question 4

What is the radiation shield in an x-ray tube?

Answer 4

Minimises leakage of scattered radiation

Question 5

What are the cooling fins in an x-ray tube?

Answer 5

Often have coolant running through to extend the life of the tube components. Only about 1% of electrical input goes into creating electrons, the rest creates heat which can damage components if raised above a critical temp

Question 6

What is the purpose of the thin glass window in an x-ray tube and how does it achieve this?

Answer 6

The glass window will be transparent to higher energies but will absorb low energy x-rays, hardening the beam, and lowering the skin dose to patients due to absorption and attenuation of the beam

Question 7

What are the features of a linear accelerator head (MV photons)?

Answer 7

1. Removable X-ray target
2. Primary collimator
3. Flattening filter
4. Ionisation chamber
5. Secondary collimator (jaws)
6. Tertiary collimator (MLC / multi-leaf collimator)

Question 8

What are some of the implications of removing the flattening filter? How is this clinically useful?

Answer 8

Slightly softer beam as less filtration, much higher dose rates available, quicker treatments