Biological Effects of Radiation

Question 1

What are the three electron interactions with matter?

Answer 1

Ionisation
Excitation
Heat Production

Question 2

What is the energy loss of an electron for each ionisation caused?

Answer 2

34eV

Question 3

State and explain the three light production methods on irradiation.

Answer 3

fluorescence: prompt light emission
phosphorescence: delayed light emission
thermoluminescence: light emission when heated

Question 4

Explain how indirect damage can arise from radiation.

Answer 4

Action of radiation leads to excited macromolecules (RH -> RH*) and then to the production of free radicals R• and H •

Question 5

Which is more likely at diagnostic levels: direct or indirect action?

Answer 5

Indirect

Question 6

Define Linear Energy Transfer (LET)

Answer 6

LET is a measure of the rate at which energy is transferred to the medium (i.e. ionisation density along the track of the particle)
A more penetrating beam has a lower LET

Question 7

Define Radiobiological Effectiveness (RBE)

Answer 7

RBE = dose of 200kVp x-rays/dose of other radiation to give same biological effect

Question 8

What does RBE vary with?

Answer 8

• dose
• dose rate
• fractionation
• physiological conditions (e.g. oxygen concentration)
• biological species
• biological end point chosen for comparison
• time after irradiation when measurements made