Biological Effects

Question 1

Give three electron interactions in tissue? (6 marks)

Answer 1

• Ionisation of molecules such as water forming harmful hydroxl ions.
• Thermal energy can be deposited, where energy is given to the whole atom.
• Excitation where energy is given to the outer shell electrons and the atom is made more reactive.

Question 2

Give four general effects of radiation in tissue? (4 marks)

Answer 2

• Ionisation, biological, chemical and thermal effects.

Question 3

What ways can biological damage be delivered to tissue via radiation? (2 marks)

Answer 3

• Directly via radiation damage causing breaks in the DNA chain. A double strand break is required for lethal damage.
• Most of the damage is done indirectly via ions generated from radiation, such as the hydroxl ion generated in water.

Question 4

Define what is meant by the LET? (2 marks)

Answer 4

Refers to the rate of energy transfer in tissue; it is higher at lower energies due to the increased probability of the PE effect.

Question 5

What biological effects are there of WB doses? (4 marks)

Answer 5

Erythema (deterministic), loss of hair, nausea, death, secondary cancer induction (stochastic process).

Question 6

What is the RBE? And what factors affect the RBE (4 marks)

Answer 6

Relative biological effectiveness:

ratio of biological effect of dose delivered to the same dose delivered at 200 keV energy.

Varies with age, sex, species…