Radiobiology

Question 1

What were the important years for discovering X-rays and its effects?

Answer 1

X-rays discovered 1895.

Within months, X-rays were being used for diagnostic purposes.

Natural radioactivity was discovered 1896.

As early as 1896 x-ray operators and their patients began reporting skin conditions and alopecia.

The first reported case of skin cancer caused by x-rays was not for another six (6) years (1902) and not confirmed by experimentation for an additional eight (8) years (1908).

In 1915 the British Roentgen Ray Society recommended safety precautions.

Seven (7) years later (1922) the American society followed suit.

Question 2

What were the different ways that research and knowledge was gained about X-rays?

Answer 2

Cohort studies of people previously been exposed to radiation.

1929 - 1943 = incidence of leukaemia and affect on life span.

1945 - japanese atomic bombs survivors

1926- 57 - review of 3000 children with enlarged thymus

Question 3

What are the 2 ways to classify how radiation affects biologic response?

Answer 3

Stochastic and deterministic

Question 4

Stochastic effect

Answer 4

Occurs at random
Takes a long time to appear (years to decades) (latent)
increase dose -> increase probability
There is no threshold dose. Any exposure can cause damage. This is an issue for staff and patients. Therefore, ALARA is used.

Examples of stochastic effects are radiation induced cancers and hereditary effects.

Question 5

Deterministic effect

Answer 5

Acute radiation effects
High dose
Short time period
Not random
Threshold
Causes cell mutation and death. Skin erythema, cataracts and acute radiation sickness.
Probability remains the same with increased dose but severity increases.

Question 6

What are the 3 major general effects of radiation on the person?

Answer 6

Somatic, Genetic, teratogenic

Question 7

What is the target molecule for radiation?

Answer 7

DNA

Question 8

What are two types of radiation interactions that produce biological changes?

Answer 8

DIRECT and INDIRECT

Question 9

DIRECT interactions?

Answer 9

According to target theory, cell death will only occur if the target molecule is inactivated. i.e. DNA is damaged.

DIRECT is the result of ionisation or excitation of DNA, RNA or Protein molecules.

Question 10

INDIRECT

Answer 10

INDIRECT refers to effects as a result of interactions within the surrounding medium.
ionise water to free radicals that transfer their energy to DNA.
Free radical induced damage to DNA is the primary cause of biologic damage in low LET radiation.
Because of the high water content of tissues (80%) and DNA being less than 1% of the cell volume, most interactions are INDIRECT.

Question 11

LET

Answer 11

LET is Linear Energy Transfer and is a measure of the rate at which energy is transferred from ionising radiation to tissues.

Question 12

What are the radiation related factors that determine how badly the body is affected?

Answer 12

Time of exposure
The way the tissue was exposed
What are the types and energy of radiations
What was the dose rate and absorption dose

Question 13

What are the biological related factors that determine how badly the body is affected?

Answer 13

Condition of the cells at the time of irradiation i.e. are they reproducing
Which cells and organs are affected and whether they are important cells or organs.

Question 14

Cell sensitivity is determined by?

Answer 14

Have a high division rate
Have a high metabolic rate
Are of a non specialised type
Are well nourished

Lymphocytes (white blood cells) and cells which produce blood are constantly regenerating, and therefore the most sensitive.

Reproductive and GI cells do not regenerate as quickly, so are slightly less sensitive.

Nerve and muscle cells are the slowest to regenerate and are therefore the least sensitive.

Question 15

main chain scission is?

Answer 15

MAIN-CHAIN SCISSION This is the breakage of the backbone of a molecule or DNA strand. In DNA it can sever one or both side rails of the strand.

Question 16

CROSS LINKING

Answer 16

When the side rail on a DNA strand is broken, it may slip and cross link

Question 17

POINT LESSION

Answer 17

A disruption of a single chemical bond which is not detectable but can cause malfunction within the cell.

Question 18

What is the organ sensitivity determined by?

Answer 18

Factors affecting sensitivity include

Rate of Reproduction

Oxygen Supply (O2 leads to  production of free radicals)

1. Sensitivity of organs relate to sensitivity of tissues
2. Sensitivity is measured by organ function that cell survival

Question 19

Regeneration (Repopulation)

Answer 19

Replacement of damaged cells by the same cell type, full functionality of the organ is give back. Radiosensitive tissues can go back to normal. Skin, G.I. tract, bone marrow

Question 20

Repair

Answer 20

Repairing of damaged cells by fibrous scar tissue, organ function is compromised. Radioresistant tissues can only repair. CNS, nerve and muscle

Question 21

What are the 5 R’s of Fractionation?

Answer 21

Fractionation is giving small doses of radiation at regular intervals. 
REPAIR
REDISTRIBUTION
REOXYGENATION
REPOPULATION
RADIOSENSITIVITY

Question 22

Whole body sensitivity is determined by?

Answer 22

Total dose
Type of cell 
Type of radiation
Age of the individual
Stage of cell division
Part of the body exposed 
General state of health 
Tissue volume exposed
Time interval over which the dose is received

Question 23

What are the two variations of exposure and time of exposure and what effects does it have on tissue? Why does the tissue react like this?

Answer 23

High dose over brief intervals:
tissue effects = acute or short term
Reason = person’s health is bad so increase susceptibility

Low dose over extended period:
tissue effects = chronic or long term effects at the level of the cell. The effects will remain for years or decades.

High doses tend to kill cells
Low doses tend to damage or change cells

Question 24

ARS (acute radiation sickness)

Answer 24

high acute radiation dose,
series of clinical responses
full body response.
Sub-syndromes seen after a while within hours to weeks
Stages are = Prodormal, latent, manifest illness, death/recovery

Question 25

Prodormal

VAN DADS

Answer 25

Dose dependent and can begin within minutes to hours after exposure.Symptoms: Anorexia, nausea, vomiting, diarrhoea, increased salivation, abdominal cramps and dehydration.

Question 26

Latent

Answer 26

The prodromal symptoms subside. Like an incubation period during which the organ system damage is progressing. Stage which may last days to weeks.

Question 27

manifest illness

Answer 27

Abrupt onset of moderate to severe symptoms relevant to the underlying organ system damage.

Question 28

Death/recovery

Answer 28

weeks to months

Question 29

supra-lethal doses in excess of 50 Gy

Answer 29

die within 24 – 48 hours from complications of neurovascular syndrome.

Symptoms.
A rapid onset of oedema, increased intracranial pressure, lethargy and prostration. If that weren’t enough, they then usually have seizures which range from random muscle contractions to generalised tonic colonic ending in ataxia and death.

There would also be cardiovascular involvement characterised by blood pressure depression, arrhythmias and shock

Question 30

People exposed to 10 - 50 Gy

Answer 30

often go through prodromal and latent periods before they exhibit gastrointestinal syndrome symptoms.

Symptoms.
Direct damage to the GI tract make the body unable to absorb nutrients. This damage also leads to massive infections as GI flora no longer contained within the GI tract. Patient would also be suffering from hematopoietic syndrome too

Generally GI syndrome leads to death within 3 – 10 days if no medical care given or as long as 2 weeks if intensive medical support is given.

Question 31

People exposed to 0.5 – 10 Gy

Answer 31

often go through prodromal and latent periods before they begin to exhibit hematopoietic syndrome symptoms.

Symptoms.
Haemorrhage, ulceration, infection due to the destruction of both red and white blood cells. Also epilation (hair loss). Most will also show GI symptoms due to damage to the mucosal barrier

Question 32

doses lower than 2 Gy.

Answer 32

Healthy adults with proper medical care almost always recover

Question 33

Death Due to ARS is an Example of

Answer 33

deterministic effect

Question 34

ARS doses in Sv

Answer 34

20 Sv. Death in hours due to severe damage to central nervous system .

10 Sv. Death in days due to damage to lining of the GI tract. Infection enters blood. Patient dies of septicaemia or haemorrhage as a result of the breakdown of the gut lining.

5 Sv. Death within weeks due to bone marrow failure (unless medical intervention).

1 Sv. Survival with low blood count.

Question 35

The amount of radiation dose to kill is large.

What are the lethal doses to humans.

Answer 35

The LD50/60 for humans is 3 - 5 Sv delivered rapidly.

The LD50/60 for humans may extend to 6 Sv with supportive medical care such as transfusions and antibiotics and possibly as high as 6 – 8 Sv in an intensive care system