Electron Treatment Planning

Question 1

What is the energy range of the clinical electron beam?

Answer 1

4 to 20 MeV

Question 2

What is the ideal tumor depth for electron?

Answer 2

Less than 4 to 5 cm

Question 3

What are the unique properties of electron beam vs. photon beams?

Answer 3

• Sharp depth dose fall-off
• Higher surface dose (higher the energy higher surface dose, unlike photon in which case that higher energy photon has lower surface dose)
• Little effect on distant organs unlike photons

Question 4

What are the two types of electron interactions (collisions)?

Answer 4

Inelastic and elastic collisions

Question 5

What are the two types of inelastic collisions?

Answer 5

1. With atomic electrons (ionization & excitation)

2. With nuclei (Bremsstrahlung)

Question 6

What is the main role of scattering foil?

Answer 6

Converts pencil beam to a broad beam

Question 7

What is the purpose of a primary foil and a secondary foil in the dual scattering foils?

Answer 7

The primary foil is made of high Z material and serves to give the highest scattering power vs. collision stopping power. Thickness is usually 0.05 - 0.4 mm

The secondary foil is made of lower Z material is used to reduce Bremsstrahlung production

Question 8

What is different about the penumbra of electron compared to photon?

Answer 8

Photon has a smaller penumbra

Question 9

Roles of bolus?

Answer 9

1. Increase surface dose
2. Pull the dose away from OARs
3. Makes incident surface more regular
4. Can be used to customize doses