National Committee for the Certification of Radiation Protection Officer BIOLOGICAL EFFECTS OF IONIZING RADIATION

National Committee for the Certification of Radiation Protection Officer Contents Introduction Radiation Injury Mechanism Factors That May Modify Radiation Effects Biological Effects Risk Estimates Summary

National Committee for the Certification of Radiation Protection Officer Introduction 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.

National Committee for the Certification of Radiation Protection Officer Levels of Radiation Effects Molecular Level Cellular Level Organ Level Whole Body Level

National Committee for the Certification of Radiation Protection Officer Radiation 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.

National Committee for the Certification of Radiation Protection Officer 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

National Committee for the Certification of Radiation Protection Officer 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.

National Committee for the Certification of Radiation Protection Officer Biological Effects Radiological sensitivities of cells:  Types of cells  Divisional activities Genetic and somatic damage (define). Deterministic and stochastic effects.

National Committee for the Certification of Radiation Protection Officer Biological Effects (cont.) Deterministic Effect Stochastic Effect BIOLOGICAL Dominant Recessive SOMATIC GENETIC

National Committee for the Certification of Radiation Protection Officer Biological Effects (cont.) SOMATIC GENETIC BIOLOGICAL Hereditary effect (Stochastic effect) Stochastic Effect Carcinogenic effect (Stochastic effect) Deterministic Effect Partial exposure - Hematopoietic - Intestinal - Skin - Lung Whole body exposure - BM, GI and CNS syndrome

National Committee for the Certification of Radiation Protection Officer Biological Effects (cont.) BIOLOGICAL SOMATIC GENETIC Dominant Recessive Effects on sperms and eggs (Deterministic effects) Effects on sperms and eggs (Deterministic effects)

National Committee for the Certification of Radiation Protection Officer 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.

National Committee for the Certification of Radiation Protection Officer 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.

National Committee for the Certification of Radiation Protection Officer Stochastic Effect Carcinogenesis 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.

National Committee for the Certification of Radiation Protection Officer 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 Effect Hereditary

National Committee for the Certification of Radiation Protection Officer 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.

National Committee for the Certification of Radiation Protection Officer Four 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.

National Committee for the Certification of Radiation Protection Officer 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 LD 30/60 is about Gy.

National Committee for the Certification of Radiation Protection Officer Acute Radiation Syndrome following acute exposure to low LET uniform whole body radiation of human being (ICRP #60) Whole body absorbed dose (Gy) Radiation syndromeTime of death after exposure (days) >15 Bone Marrow Syndrome Gastrointestinal Syndrome and lungs Central Nervous System Syndrome –

National Committee for the Certification of Radiation Protection Officer 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.

National Committee for the Certification of Radiation Protection Officer Gastrointestinal Syndrome (GIS) Full syndrome usually occurs with a dose of between Gy. Syndrome causes damages to the gastro-intestinal system. Prognosis 100%.

National Committee for the Certification of Radiation Protection Officer 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 days.

National Committee for the Certification of Radiation Protection Officer Risk Estimates Cancer Type Probability of Fatal Cancer, Sv -1 Bone Marrow 50 Bone surface 5 Lung 85 Thyroid 8 Breast20 Colon85 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 Sv -1 year -1 for the risk of genetic effects due to exposure to radiation

National Committee for the Certification of Radiation Protection Officer Cancer Type Probability of Fatal Cancer, Sv -1 Stomach 110 Bladder 30 Oesophagus 30 Liver 15 Skin 2 Gonad 10 Others 50 TOTAL 500 x Sv -1 Risk Estimates (cont.)

National Committee for the Certification of Radiation Protection Officer Summary

National Committee for the Certification of Radiation Protection Officer Thank You Thank You for your attention