LET & RBE

Question 1

Linear Energy Transfer

Answer 1

Average energy deposited per unit track length (keV/um)

Question 2

Low LET Radiations

Answer 2

X-Rays

Gamma Rays

High Energy Beta particles

Question 3

High LET Radiations

Answer 3

Alpha particles

Low Energy Beta particles

Protons

Neutrons

Question 4

LET vs. Energy for photons

Answer 4

LET tends to increase with photon energy until very high energies

Question 5

Relative Biological Effectiveness

Answer 5

The ratio of the standard dose to the test dose required for equal biological effect.

Question 6

RBE depends on…

Answer 6

Radiation Quality

Biological Endpoint

Biological System

Choice of radiation “standard”

Radiation dose and dose rate

Number of dose fractions

Question 7

Relationship between RBE and LET

Answer 7

RBE increases with LET up to about 100 keV/um

Question 8

Optimal LET

Answer 8

About 100 keV/um

Greatest RBE because the separation between ionizing events is approximately equal to the diameter of the DNA double helix, leading to the highest probability of double strand break per dose