Hall 25 - Alternative Radiation Modalities

Question 1

What kind of ionization do neutrons cause?

Answer 1

Indirectly ionizing
Produce recoil protons, alpha particles, heavy nuclear fragments

Question 2

What is the LET of neutrons and how do they differ radiobiologically from photons?

Answer 2

High LET
Low OER
No/less SLD
No/less cell cycle variation/sensitivity

Question 3

What is the RBE of protons?

Answer 3

1.1
Proton LET/RBE peaks at Bragg peak (depth increases with increasing energy)

Question 4

What advantage do carbon ions have over protons?

Answer 4

LET/RBE is low in the entrance region (better normal tissue sparing) and peak in Bragg peak with high RBE (more effective for tumor kill)

Less scattering (sharper penumbra) but small tail of fragments beyond Bragg peak

Question 5

How can you verify the location of spread-out Bragg peak for carbon ions?

Answer 5

PET

Carbon ions can lose 1 or 2 neutrons to unstable C-11 or C-10 > decay via beta+ > annihilation gamma ray detected by PET