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BIOLOGICAL EFFECTS OF IONIZING RADIATION
ContentsContents
• Introduction• Radiation Injury Mechanism• Factors That May Modify Radiation
Effects• Biological Effects• Risk Estimates• Summary
IntroductionIntroduction
• The final concern of radiation hazard is its effect on living things.
• The biological effects of ionizing radiation begin with the transfer of radiation energy at the molecular level and culminates with possible damage to the individual.
• At different levels the cells or organisms different types of changes are expressed.
• Damage cells may eventually cause cell death or induce the abnormal cell.
Levels of Radiation EffectsLevels of Radiation Effects
Molecular Level
Cellular Level
Organ Level
Whole Body Level
Radiation Injury MechanismRadiation Injury Mechanism
• Radiation effects begins at the physico-chemical level in cells.
• Interaction of radiation with water is the main basis for biological effects.
• Two type of radiation interactions: Direct and Indirect interactions
• DNA is the primary radiation target.
• Depending on the dose received by the cells, radiation can alter cell’s characteristics and functions, and may cause cell death.
Biological Factors
Types of cells
Activeness in cell division
Stages in the cell cycle
Factors affecting CELLULAR responses
Physical Factors
Type of radiation (LET, RBE), dose, dose rates, dose fractionation
Environmental Factors
Radiation Sensitizers and protectors, OER
Factors That May Modify Radiation Effects
Factors That May Modify Radiation Effects
Factors That May Modify Radiation Effects (cont.)
Factors That May Modify Radiation Effects (cont.)
• Other factors affecting at whole organism levels:
Types of radiation. Total dose and dose rate. Parts of the body of total body exposure. Different organs of the body. Location of the radiation source relative to target
organ. Non-uniform distribution of radionuclide inside the
body.
Biological EffectsBiological Effects
• Radiological sensitivities of cells: Types of cells Divisional activities
• Genetic and somatic damage (define).
• Deterministic and stochastic effects.
Biological Effects (cont.)Biological Effects (cont.)
Deterministic Effect
Stochastic Effect
BIOLOGICALDominant
Recessive
SOMATIC
GENETIC
Biological Effects (cont.)Biological Effects (cont.)
SO
MA
TIC
GENETIC
BIO
LO
GIC
AL
Hereditary effect (Stochastic effect)Hereditary effect (Stochastic effect)
Sto
chas
tic
Eff
ect
Carcinogenic effect (Stochastic effect)
Carcinogenic effect (Stochastic effect)
Det
erm
inis
tic
Eff
ect
Partial exposure - Hematopoietic- Intestinal- Skin- LungWhole body exposure - BM, GI and CNS syndrome
Biological Effects (cont.)Biological Effects (cont.)
BIOLOGICAL
SOMATIC
GENETIC
Dominant
Recessive
Effects on sperms and eggs
(Deterministic effects)
Effects on sperms and eggs
(Deterministic effects)
Deterministic vs Stochastic Effects Deterministic vs Stochastic Effects
• Effects of radiation on biological system is generally divided into TWO, ie somatic and genetic.
• Both types of effects is NOT favored in radiation protection. In radiation protection a quantitative assessment of effects or risks is preferred.
• In 1990, ICRP # 60 proposed Deterministic and Stochastic Effects.
Deterministic vs Stochastic Effects (cont.)
Deterministic vs Stochastic Effects (cont.)
• Deterministic effects: There exist threshold levels for deterministic effects. Severity of its effect is proportional to the dose
received.
• Stochastic effects: Occurrence of effect is probabilistic in nature.
Example: cancer. Probability of its occurrence is proportional to the
dose received. Threshold level of radiation dose does not exist for
stochastic effect.
Stochastic EffectCarcinogenesis
Stochastic EffectCarcinogenesis
• Carcinogenesis is an example of somatic stochastic effect.
• Carcinogenesis may: Occur after low dose exposure; and The probability of malignancy increases with increase in dose.
• In man there is a latent period between initiation and expression of effects. Latent period is about 8 years for induced leukemia and 2-3 X longer for solid tumor (eg lung and breast cancers).
• Stochastic effect is influenced by LET and dose rate.
• Occurs in germinal cells of the gonads.
• Radiation induces changes in genetic information (through mutation or chromosomal aberrations) and subsequently expressed in the next generation.
• Stochastic hereditary effect may be divided into different categories based on severity of genetic effects. Dominant mutation: fatality may be expressed in the first
generation. Recessive mutation produces less effect to the first generation
but more towards increasing the content of genetic damage in the general genetic pool.
Stochastic EffectHereditary
Stochastic EffectHereditary
Acute Radiation Syndrome (ARS)Acute Radiation Syndrome (ARS)
• Caused by acute high dose exposure (> 0.5 Sv) to the whole body.
• Usually due to external exposure.
• ARS is divided into three types:Bone Marrow Syndrome;Gastrointestinal Syndrome; and Central Nervous System Syndrome.
Four stages in ARSFour stages in ARS
• Prodromal Syndrome: Classic symptoms include nausea, vomiting,
possibly diarrhoea occurring within minutes - days following exposure. Symptoms last from minutes - several days.
• Latent Stage: Where patient looks and feels healthy for few
hours - weeks.
Four stages in ARS (cont.)Four stages in ARS (cont.)
• Manifest Illness Stage: Depends on the specific radiation syndrome (BMS,
GIS, CNSS). Illness last between hours – months.
• Recovery or Death Stage: Patient either recovers or dies. In case of CNSS there is no recovery and death
within days of exposure. Recovery may occur for BMS although the LD30/60 is about 2.5 - 5 Gy.
Acute Radiation SyndromeAcute Radiation Syndromefollowing acute exposure to low LET uniform whole body radiation of following acute exposure to low LET uniform whole body radiation of
human being (ICRP #60)human being (ICRP #60)
Whole body absorbed dose
(Gy)
Radiation syndrome Time of death after
exposure (days)
3-5
5-15
>15
Bone Marrow Syndrome
Gastrointestinal Syndrome and lungs
Central Nervous System Syndrome
30-60
10 – 20
1-5
Bone Marrow Syndrome (BMS)Bone Marrow Syndrome (BMS)
• Following acute exposure to dose 3 – 5 Gy.
• Mild symptom may occur as low as 0.3 Gy.
• Syndrome is caused by damages to the blood system and stem cell.
• Symptoms: nausea, vomiting and paleness.
• Changes blood picture.
Gastrointestinal Syndrome (GIS)Gastrointestinal Syndrome (GIS)
• Full syndrome usually occurs with a dose of between 5 -15 Gy.
• Syndrome causes damages to the gastro-intestinal system.
• Prognosis 100%.
Central Nervous System Syndrome (CNSS)
Central Nervous System Syndrome (CNSS)
• Syndrome occur with dose > 15 Gy.
• Death due to damages to central nervous system.
• Victims suffer motor incoordination, convulsion, coma and death.
• Prognosis is 100% death within 1 - 5 days.
Risk EstimatesRisk Estimates
Cancer Type Probability of Fatal Cancer, 10-4 Sv-1
Bone Marrow 50 Bone surface 5
Lung 85Thyroid 8Breast 20Colon 85
TOTAL cont. …
Estimates of probabilities of occurrence for various types of cancer due to exposure to radiation
ICRP gave the value of 0.6 x 10-2 Sv-1 year-1 for the risk of genetic effects due to exposure to radiation
Cancer Type Probability of Fatal Cancer, 10-4 Sv-1
Stomach 110Bladder 30Oesophagus 30Liver 15Skin 2Gonad 10Others 50
TOTAL 500 x 10-4 Sv-1
Risk Estimates (cont.)Risk Estimates (cont.)
Thank YouThank Youfor your attention