Module 5: Radiation Biology - Clinical Effects

CLINICAL EFFECTS:

The clinical picture depends on which of the cellular outcomes is predominant. Two distinct clinical effects exist: DETERMINISTIC and STOCHASTIC.

Deterministic effects:

1. Due to cell death.
2. Usually high dose accidental exposure.
3. Visible damage.
4. Threshold value applies.
5. Severity of effect is related to dose.

Then tissues that are most sensitive to radiation are those that undergo rapid turnover. These are known as radiosensitive tissues:

1. Germinal tissue.
2. Haematopoetic Tissue.
3. Epithelium - skin/GIT.
4. Cornea.

Dose and Clinical Effect:

0 - 100 cGy - Subclinical
100 - 800 cGy - Haematopoetic
> 600cGy - Respiratory
800 - 3000cGy - GIT
> 3000cGy - CVS/CNS

Acute Radiation Syndrome:

Acute radiationsyndrome is an acute illness that follows a predictable course over a period of time ranging from a few hours to several weeks after exposure to ionizing radiation.

Development of groups of signs and symptoms that are manifestations of the reactions of various body systems to irradiation. The prodrome is

• Anorexia.
• Nausea.
• Vomiting.
• Diarrhoea.
• Fever.
• Conjunctivitis.
• Skin Erythema.

The onset of symptoms is dependent on dose received.

Haematopoetic Syndrome:

• Due to bone marrow depression.
• Initial granulocytosis.
• Typically pancytopaenia.
• Anaemia.
• Clotting abnormalities.
• Immune suppression.

GIT Syndrome:

• Malabsorption.
• Ileus.
• Electrolyte imbalance.
• GI bleeding.

Cerebrovascular/CNS Syndrome:

• Vomiting.
• Confusion and disorientation.
• Severe hypotension.
• Cerebral oedema.
• Convulsions - coma.
• Hyperpyrexia.
• Death.

Stochastic Effects:

Stochastic effects are by nature:

• Random.
• No dose below which there is no effect.
• Dose is related to probability of effect.
• Somatic or reproductive gene mutations.
• Effect may be expressed in exposed population or progeny.
• Effects may be felt years, decades after exposure.

CANCERS associated with radiation:

• Leukaemia (except CLL).
• Thyroid cancer.
• Lung cancers.
• Bone.
• Skin.
• Liver.

Hereditary Genetic Effects:

• Polydactyly.
• Achondroplasia.
• Huntington’s Chorea.
• Muscular Dystrophy.
• Retinoblastoma.

Clinical Effects Summary: