Deterministic effect

Question 1

Unexpected outcomes of radiation

Answer 1

• Bystander effect
• Genomic instability
• Adaptive responses/hormesis

Question 2

Bystander effect

Answer 2

When the irradiated (damaged) cells send signals to the neighboring cells,
disrupting their normal function.
 A number of experiments have demonstrated that radiation does not need to
deposit energy in the cell nucleus in order to produce cell death.
 Chromosome aberrations and cell death have been observed in cells which have not
been directly targeted by a toxic agent, such as radiation.

Question 3

Genomic instability

Answer 3

Genetic mutations and chromosomal damage can occur many
cell generations after the actual irradiation
It is a delayed mechanism of radiation damage

Question 4

Adaptive Responses/Hormesis

Answer 4

The phenomenon that radiation effects are less pronounced in some
cells that have received a prior small dose of radiation

Question 5

Early effect

Answer 5

a radiation response that occurs within minutes or days after
radiation exposure.

Question 6

Late Effect

Answer 6

a radiation response that is not observed for 6 months or more after
the exposure.

Question 7

Acute Radiation Syndrome

Answer 7

caused by a high dose of radiation in a very short
period of time (usually a matter of minutes). This results in cell death and in
extreme cases causes organ damage or whole body response

Question 8

Chronic radiation syndrome

Answer 8

caused by low doses of irradiation over long

periods of time. This does not cause any immediate organ/whole body response.

Question 9

Somatic Effect:

Answer 9

limited to and manifested within the lifespan of the

exposed person by affecting somatic/non-reproductive cells

Question 10

Genetic effect

Answer 10

affecting reproductive cells (e.g. egg or sperm cells)

and radiation damage can appear in offspring of the exposed person

Question 11

Stochastic effect

Answer 11

the probability or frequency of the biologic response to radiation
as a function of radiation dose. Disease incidence increases proportionally with
dose, and there is no dose threshold.

Question 12

Deterministic Effect

Answer 12

also termed as tissue reaction, is a biologic response whose
severity varies with radiation dose and a dose threshold usually exits

Occur due to cell death (loss of function permanent or temporary)

Question 13

Factors affecting the threshold dose

Answer 13

Factors affecting the threshold dose are:
 Tissue Type: some organs can cope with a small loss of cells without a loss of
tissue function. However, as the dose increases above the threshold the probability
of causing harm will sharply increase to 100%.
 State of Health: varies for different people. Individuals already in a state of health
approaching the pathological will reach that condition earlier than healthy people.
 Dose Rate and Delivery Mode: dose fractionation and decreasing the dose rate
increases the threshold in most cases.

Question 14

Deterministic effect of whole body irradiation

Answer 14

o Acute radiation syndromes (or sickness):
central nervous system (CNS)/cerebrovascular syndrome, gastrointestinal (GI)
syndrome, haematopoietic/bone marrow syndrome
o Death

Question 15

Deterministic effect of Local tissue irradiation

Answer 15

o Cataract (opacity of the lens)
o life shortening
o Sterility
o epilation (hair loss)
o erythema (skin reddening)

Question 16

Secondary deterministic effects

Answer 16

o Damage to supporting blood vessels leading to tissue damage.
o Replacement of functional cells by fibrous tissue causing a reduction in organ
function.

Question 17

Whole Body Irradiation - CNS (Cerebrovascular) Syndrome

Answer 17

Always fatal.
• Death “appears” to be a result of elevated fluid content of the brain. 
• Observed damage are to the
nerve cells in the brain
blood vessels in the brain

Question 18

Whole Body Irradiation - Gastrointestinal (GI) Syndrome

Answer 18

 Always fatal.
 Primary damage is to stem cells of GI tract (the villi do not regenerate): 
death occurs principally due to sever damage to the cells lining the 
intestine.
 Effect is to cause problems with
absorption of metabolites
fluid loss
electrolyte balance
infection

Question 19

Whole Body Irradiation – Haematopoietic/Bone Marrow Syndrome

Answer 19

 Damage by a reduction in the number of circulating blood cells: i.e. white
blood cells (WBC), red blood cells (RBC) and platelets.
 Causes of the damage are:
direct destruction of circulating WBC
haemorrhage
inhibition of blood cell production

Question 20

What is the LD50/30?

Answer 20

The LD 50/30 is the dose of radiation to the whole body that results in death
within 30 days to 50% of the exposed population.

Question 21

Why defining LD50?

Answer 21

The radiation dose-response is not the same for everyone.
It is used as a quantitative measure of acute radiation lethality in terms of
number of days from the radiation exposure until death

Question 22

What Factors Modify the LD50?

Answer 22

Physical Factors:
Dose Rate
Type of Radiation
Partial Body Shielding

Biological Factors:
Medical Support
Age
Health and Diet

Chemical Factors:
Oxygen

Question 23

 The estimated LD50/30 for humans

Answer 23

3-5gy

Question 24

annual limit for skin dose

Answer 24

500 mSv.cm-2 (occupational)
50 mSv.cm-2
(public)

Question 25

Annual limit of dose for the eye

Answer 25

150 mSv (occupational) 
15 mSv (public)

Question 26

Internal exposure limit

Answer 26

Internal exposure is limited to effective dose 20 mSv (ICRP61).

 Intakes may be averaged over 5 years - similar manner to external
exposure.