Radiobiology

Question 1

What is a direct effect caused by?

Answer 1

Caused by photon having a ‘direct hit’ on cell structures/chromosomes

Question 2

What is indirect effect caused by?

Answer 2

Ionization of water in a cell leads to a free radical
H2O → photon = HOH+• + e-
Free radical causes damage

Sometimes it recombines and doesn’t cause issues.

Question 3

What is radiolysis?

Answer 3

Radiolysis is the dissociation of molecules by ionizing radiation.
It is linked to both direct and indirect effects.

Question 4

What can be caused by direct effect?

Answer 4

Genetic damage- offspring
Cell mutation - cancer
Overexpress chemicals - hormones
Delayed or arrested cell division - mitosis and meiosis
Cell death - apoptosis

Question 5

What can be caused by indirect effect?

Answer 5

Ionisation of water leads to a free radical
A radical is a molecule with an unpaired electron (•)
-unstable & reactive

For example, OH • Radicals can combine to form hydrogen peroxide (H2O2). This has a relative long life and is an oxidiser which causes damage to cellular molecules.

Question 6

Factors that effect tissues

Answer 6

Radiosensitivity of the tissue
Volume of tissue irradiated
Dose received

Question 7

What are the types of BIOLOGICAL EFFECTS?

Answer 7

Somatic- individual

Genetic- offspring

Question 8

Types of somatc effects

Answer 8

Acute or early effects - occur within hours or weeks. Alopecia

Late or chronic effects - chromosomal damage. May take up to 20 years
e.g cancer, fibrosis, permanent hair loss, mental retardation in children.

Question 9

What causes of genetic effects and example

Answer 9

Irradiation of gonads (sperm and ova)
Passed onto offspring
Potentially harmful only if dose received before or during reproductive period.

Leukaemia
Mental retardation
Birth defects

Question 10

Radiation effects can also be divided into:-

Answer 10

Deterministic effects (now also termed Harmful Tissue Reaction)

Stochastic effect

Question 11

Factors of deterministic effects with example

Answer 11

Occur once a theshold dose received
Severity increases with dose
Most common-
Cataract - 1Gy
Male – >500cGy Permanent sterility

Question 12

Factors of stochastic effects

Answer 12

Effect that have no threshold

Effects occur by pure chance- statistical

Frequency (incidence) increases with dose
Usually cancer