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International Atomic Energy Agency RADIATION PROTECTION IN NUCLEAR MEDICINE Part 1: Biological Effects of Ionizing Radiation

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 2 Objective To become familiar with the mechanisms of different types of biological effects following exposure to ionizing radiation and results of epidemiological studies of exposed population to ionizing radiation. To be aware of the models used to derive risk coefficients for estimating the detriment

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 3 Contents Basic concepts, cellular effects Deterministic effects Stochastic effects Effects on embryo and fetus Risk estimates

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International Atomic Energy Agency Part 1. Biological Effects Module 1.1. Basic Concepts

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 5 1895 X-rays discovered by Roentgen 1896 First skin burns reported 1896 First use of x-rays in the treatment of cancer 1896 Becquerel: Discovery of radioactivity 1897 First cases of skin damage reported 1902 First report of x-ray induced cancer 1911 First report of leukaemia in humans and lung cancer from occupational exposure 1911 94 cases of tumour reported in Germany (50 being radiologists) Early Observations of the Effects of Ionizing Radiation

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 6 Information comes from: studies of humans (epidemiology) studies of animals and plants (experimental radiobiology) fundamental studies of cells and their components (cellular and molecular biology) The key to understanding the health effects of radiation is the interaction between these sources of information. Effects of Radiation Exposure

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 7 Radiation exposure affects the center of life: the cell Chromosomes

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 8

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 9 The critical target: DNA

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 10 Interaction of ionizing radiation with DNA DIRECT ACTION INDIRECT ACTION

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 11 Damage to DNA

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 12 radiation hit cell nucleus! No change DNA mutation Exposure of the Cell

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 13 DNA Mutation Cell survives but mutated Cancer? Cell death Mutation repaired Unviable Cell Viable Cell Outcomes after cell exposure

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 14 How is DNA repaired?

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 15 Altered base Enzyme Glycosylases recognizes lesion and releases damaged base AP-endunuclease makes incision and releases remaining sugar DNA-polymerase fills resulting gap but nick remains DNA ligase seals the nick. Repair completed. DNA has been repaired with no loss of genetic information

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 16 Repair The human body contains about 10 14 cells. An absorbed dose of 1 mGy per year (natural sources) will produce about 10 16 ionizations, which means 100 per cell in the body. If we assume that the mass of DNA is 1% of the mass of the cell, the result will be one ionization in the DNA-molecule in every cell in the body each year.

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 17 order of magnitudes 999 of 1000 lesions are repaired 999 of 1000 damaged cells die (not a major problem as millions of cells die every day in every person) many cells may live with damage (could be mutated)

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 18 Cell killing Radiosensitivity RS = Probability of a cell, tissue or organ of suffering an effect per unit of dose. Bergonie and Tribondeau (1906): RS LAWS: RS will be greater if the cell: Is highly mitotic. Is undifferentiated.

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 19 RADIOSENSITIVITY High RSMedium RSLow RS Bone Marrow Spleen Thymus Lymphatic nodes Gonads Eye lens Lymphocytes (exception to the RS laws) Skin Mesoderm organs (liver, heart, lungs) Muscle Bones Nervous system

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 20 Biological Effects at Cellular Level Possible mechanisms of cell death: Physical death Functional death Death during interphase Mitotic delay Reproductive failure Cellular effects of ionizing radiation are studied by cell survival curves % survival cells (semi logarithmic) Dose n = targets DqDq D0D0 (threshold) (radiosensitivity) 100%

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 21 Physical LET (linear energy transfer): RS Dose rate: RS Temperature RS Chemical Increase RS: OXYGEN, cytotoxic drugs. Decrease RS: SULFURE (cys, cysteamine) Biological Cycle status: RS: G2, M RS: S Repair of damage (sub-lethal damage may be repaired e.g. fractionated dose) G1 S G2 M G0 LET LET % survivor cells Factors Affecting Radiosensitivity

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 22 low LET high LET low LET Absorbed dose Surviving fraction LET (linear energy transfer) is the amount of energy (MeV) a particle will loose in traversing a certain distance (m) of a material. Cell Survival Radiation Quality

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 23 Adapted from Marco Zaider (2000) Ionization Pattern

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 24 Direct effects Indirect effects Cell death Primary damage Modified cell Damage to organ Somatic cells Germ cells Hereditary effects Cancer Leukemia Death of organism Repair Deterministic effects Stochastic effects Biological Effects

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 25 Timing of Events leading to Radiation Effects

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International Atomic Energy Agency Part 1. Biological Effects Module 1.2. Deterministic Effects

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 27 Effects of Cell Death Effects of Cell Death Dose (mSv) Probability of death D 100%

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 28 0123456789 10 FREQUENCY ABSORBED DOSE SEVERITY Diagnostic threshold Threshold dose Most radiosensitive individual Most radioresistant individual Deterministic Effects

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 29 Cataracts of the lens of the eye 0.5 Gy [ICRP statement on tissue reactions (http://www.icrp.org/docs/icrp%20stateme nt%20on%20tissue%20reactions.pdf)]http://www.icrp.org/docs/icrp%20stateme nt%20on%20tissue%20reactions.pdf Permanent sterility males 3.5-6 Gy females 2.5-6 Gy Temporary sterility males 0.15 Gy females 0.6 Gy dose Severity of effect threshold Threshold Doses for Deterministic Effects

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 30 Note on Threshold Values Depend on dose delivery mode: single high dose most effective fractionation increases threshold dose in most cases significantly decreasing the dose rate increases threshold in most cases Threshold may differ in different persons

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 31 Systemic Effects Effects may be morphological and/or functional Factors: Which Organ Which Dose Effects Immediate (usually reversible): < 6 months e.g.: inflammation, bleeding. Delayed (usually irreversible): > 6 months e.g.: atrophy, sclerosis, fibrosis. Criteria of dose < 1 Gy: LOW DOSE 1-10 Gy: MODERATE DOSE > 10 Gy: HIGH DOSE Regeneration means replacement by the original tissue while Repair means replacement by connective tissue.

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 32 Skin Effects Following the RS laws (Bergonie and Tribondeau), the most RS cells are those from the basal stratum of the epidermis. Effects are: Erythema: 1-24 hours after irradiation of about 3-5 Gy Alopecia: 5 Gy is reversible; 20 Gy is irreversible. Pigmentation: Reversible, appears 8 days after irradiation. Dry or moist desquamation: traduces epidermal hypoplasia (dose about 20 Gy). Delayed effects: teleangiectasia, fibrosis. DERMIS EPIDERMIS Histologic view of the skin Basal stratum cells, highly mitotic, some of them with melanin, responsible of pigmentation. From Atlas de Histologia.... J. Boya

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 33 Skin Effects Skin damage from prolonged fluoroscopic exposure

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 34 Skin Effects By handling unshielded syringes and vials containing radioactive material the threshold dose of skin erythema will be reached in a short time. Example: The dose rate at the surface of a vial containing 30 GBq Tc99m is of the order of 2 Gy/h meaning that the threshold dose will be reached after 2 h of exposure. This corresponds to 36 s per working day in a year

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 35 Skin Effects Example: After an extravascular injection of 500 MBq of a Tc99m radiopharmaceutical, the locally absorbed dose at the injection site might be as high as 5-20 Gy!

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 36 Effects in Eye Eye lens is highly RS. Coagulation of proteins occurs with doses greater than 2 Gy. There are 2 basic effects: From Atlas de Histologia.... J. Boya Histologic view of eye: Eye lens is highly RS, moreover, it is surrounded by highly RS cuboid cells. > 0.155.0 Visual impairment (cataract) > 0.1 0.5-2.0 Detectable opacities Sv/year for many years Sv single brief exposure Effect The ICRP has stated in 2011 that the threshold for tissue reactions in lens of the eye is 0.5 Gy. http://www.icrp.org/docs/icrp%20statement%20on%20tissue%20reactions.pdf http://www.icrp.org/docs/icrp%20statement%20on%20tissue%20reactions.pdf

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 37 Eye Injuries

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 38 Whole Body Response : Adult Acute irradiation syndrome Chronic irradiation syndrome Survival time Dose Steps: 1.Prodromic 2.Latency 3.Manifestation Lethal dose 50 / 30 BMS (bone marrow) GIS (gastro intestinal) CNS (central nervous system) 1-10 Gy 10-50 Gy > 50 Gy Whole body clinic of a partial-body irradiation Mechanism: Neurovegetative disorder Similar to a sick feeling Quite frequent in fractionated radiotherapy

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 39 Lethal Dose 50/30 It is an expression of the per cent lethal dose as a function of time. It means: Dose which would cause death to 50% of the population in 30 days. Its value is about 2-3 Gy for humans for whole body irradiation.

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 40 Whole Body Exposure Absorbed dose (Gy) Syndrome or tissue involved Symptoms 1-10Bone marrow syndrome Leucopenia, thrombopenia, hemorrhage, infections 10-50GastrointestinalDiarrhoea, fever, electrolytic imbalance >50Central nervous syndrome Cramps, tremor, ataxia, lethargy, impaired vision, coma

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 41 Whole Body Exposure Absorbed dose (Gy) TherapyPrognosis 1-10Symptomatic Transfusions of leucocytes and platelets. Bone marrow transplantation Growth stimu- lating factors Excellent to uncertain 10-50PalliativeVery poor >50SymptomaticHopeless Lethality 0-90% 90-100% 100%

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International Atomic Energy Agency Part 1. Biological Effects Module 1.3. Stochastic Effects

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 43 Stochatic Effects of Ionizing Radiation

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 44 Stochatic Effects of Ionizing Radiation Health consequences of Chernobyl accident 1800 children diagnosed with thyroid cancer (1998)

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 45 Stochatic Effects of Ionizing Radiation

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 46 Frequency (%) 10 20 30 40 Absorbed dose (Gy) 10 5 0 Genetic Effects

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 47 Genetic Effects Ionizing radiation is known to cause heritable mutations in many plants and animals BUT intensive studies of 70,000 offspring of the atomic bomb survivors have failed to identify an increase in congenital anomalies, cancer, chromosome aberrations in circulating lymphocytes or mutational blood protein changes. Neel et al. Am. J. Hum. Genet. 1990, 46:1053-1072

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International Atomic Energy Agency Part 1. Biological Effects Module 1.4. Effects on Embryo and Fetus

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 49 Sensitivity of the Early Conceptus Till early 1980s, early conceptus was considered to be very sensitive to radiation - although no one knew how sensitive? Realization that: organogenesis starts 3-5 weeks after conception In the period before organogenesis high radiation exposure may lead to failure to implant. Low dose may not have any observable effect.

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 50 Incidence of Prenatal & Neonatal Death and Abnormalities Hall, Radiobiology for the Radiologist pg 365

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 51 Pre-Implantation

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 52 Pre-Implant Stage (up to 10 days) Only lethal effect, all or none Embryo contains only few cells which are not specialized If too many cell are damaged-embryo is resorbed If only few killed-remaining pluripotent cells replace the cells loss within few cell divisions Atomic Bomb survivors - high incidence of both - normal birth and spontaneous abortion

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 53

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 54 Fetal Radiation Risk There are radiation-related risks throughout pregnancy which are related to the stage of pregnancy and absorbed dose Radiation risks are most significant during organogenesis and in the early fetal period somewhat less in the 2nd trimester and least in the third trimester LessLeast Most risk

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 55 Radiation-Induced Malformations Malformations have a threshold of 100-200 mGy or higher and are typically associated with central nervous system problems Fetal doses of 100 mGy are not reached even with 3 pelvic CT scans or 20 conventional diagnostic x-ray examinations These levels can be reached with fluoroscopically guided interventional procedures of the pelvis and with radiotherapy

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 56 Central Nervous System Effects During 8-25 weeks post-conception the CNS is particularly sensitive to radiation Fetal doses in excess of 100 mGy can result in some reduction of IQ (intelligence quotient) Fetal doses in the range of 1000 mGy can result in severe mental retardation particularly during 8-15 weeks and to a lesser extent at 16-25 weeks

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 57 Heterotopic gray matter (arrows) near the ventricles in a mentally retarded individual occurring as a result of high dose in-utero radiation exposure

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 58 Effects on Embryo and Fetus

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 59 AgeThreshold for lethal effects (mGy) Threshold for malformations (mGy) 1 day100No effect 14 days250- 18 days500250 20 days>500250 50 days>1000500 50 days to birth >1000>500 Effects on Embryo and Fetus

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 60 Leukemia and Cancer Radiation has been shown to increase the risk for leukemia and many types of cancer in adults and children Throughout most of pregnancy, the embryo/fetus is assumed to be at about the same risk for carcinogenic effects as children

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 61 Leukemia and Cancer The relative risk may be as high as 1.4 (40% increase over normal incidence) due to a fetal dose of 10 mGy Individual risk, however, is small with the risk of cancer at ages 0-15 being about 1 excess cancer death per 1,700 children exposed in utero to 10 mGy

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International Atomic Energy Agency Part 1. Biological Effects Module 1.5. Risk Estimates

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 63 Risk Estimates Risk = probability of effect Different effects can be looked at - one needs to carefully look at what effect is considered: E.g. Thyroid cancer mortality is NOT identical to thyroid cancer incidence!!!! Risk estimates usually obtained from high doses and extrapolated to low doses

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 64 Epidemiological Data: Hiroshima-Nagasaki Patients with ancylosing spondylitis cervical cancer tuberculosis mastitis tinea capitis thymus enlargement thyrotoxicosis hemangiomas and more may come Chernobyl Techa river Semiplatinsk Nevada ..

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 65 Populations used in the UNSCEAR Reports

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 66 How to Use Epidemiological Data to Estimate Radiation Risks at Low Doses?

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 67 Dose-Response Curve Frequency of leukemia (cases/1 miljon) Equivalent dose (mSv)

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 68 Mortality of the Atomic Bomb Survivors Dose response curve for Solid Cancer The dose response is linear up to about 3 Sv with a slope of 0.37 ERR/Sv The excess lifetime risk per Sv for those exposed at age 30 is estimated at 0.10 and 0.14 for males and females respectively The lowest dose at which there is a statistically significant excess risk is shown to be 50 mSv Pierce DA et al, Rad Res 1996; 146:1-27

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 69 Latest news from the Hiroshima-Nagasaki Cohort Extra years 1986-1990 There are now 10 500 survivors with DS86-dosimetry out of a total population of 86 572, who were irradiated 44% had died by the end of 1990. The data is incomplete in that deaths in the first five years are not included. 7 827 have died from cancer, there being 420 excess cancer deaths. 1945-19501950-90 (1986-90) Leukemia? 87 (3) Solid cancer?335 (88) ------------------------------------------------------------------- 420 Risk for children/Risk for adults = 1.4 - 1.7

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 70 Radiation Risks Linear-Quadratic Model

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 71 What happens at the low-dose end of the graph? a)Linear extrapolation b)Threshold dose c)Lower risk per dose for low doses d)Higher risk per dose for for low doses

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 72 Low doses: 15% incidence of genetic abnormalities 4- 10% intrauterine growth retardation 4% incidence of major malformation 2- 4%

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 89 Probability of bearing healthy children as a function of radiation dose

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 90 Approximate fetal whole body dose (mGy) from common nuclear medicine procedures done in early and late pregnancy ProcedureActivity (MBq) Early 9 months Tc-99m Bone scan Lung V/Q scan Liver colloid Thyroid scan Renal DTPA Red Cell 750 240 300 400 750 930 4.7 0.9 0.6 4.4 9.0 6.0 1.8 0.9 1.1 3.7 3.5 2.5 I-123 Thyroid uptake 300.60.3 I-131 Thyroid uptake 0.550.040.15

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 91 Doses and Risks for in Utero Radiodiagnostics Exposure Mean fetal dose Hered. Disease Fatal cancer (mGy) to age 14 y X-ray Abdomen2.66.2 10 -5 7.7 10 -5 Barium enema 163.9 10 -4 4.8 10 -4 Barium meal2.86.7 10 -5 8.4 10 -5 IV urography3.27.7 10 -5 9.6 10 -5 Lumbar spine3.27.6 10- 5 9.5 10 -5 Pelvis1.74.0 10 -5 5.1 10 -5 Computed tomography Abdomen8.01.9 10 -4 2.4 10 -4 Lumbar spine2.45.7 10 -5 7.1 10 -5 Pelvis256.1 10 -4 7.7 10 -4 Nuclear medicine Tc bone scan3.37.9 10 -4 1.0 10 -4 Tc brain scan4.31.0 10 -5 1.3 10 -4

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 92 Comment on Fetus/Embryo Fetus/embryo is more sensitive to ionizing radiation than the adult human Increased incidence of spontaneous abortion a few days after conception Increased incidence Mental retardation Microcephaly (small head size) especially 8-15 weeks after conception Malformations: skeletal, stunted growth, genital Higher risk of cancer (esp. leukemia) Both in childhood and later life

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 93 Scale of Radiation Exposures Annual Background CT scan Bone scan Typical Radiotherapy Fraction

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 94 Example for Risk Calculation Assume Risk of 0.05 per Sv 1,000 people are exposed to 5 mSv/y for 20 y Expected additional cancer deaths is 0.05 [cancers/Sv]x0.005[Sv/y]x20[y]x1,000[people] = 5 additional cancer deaths due to radiation (5/1000) General population: 23% (230/1000) of all deaths due to cancer (difficult to ascertain 5 additional ones caused by radiation) Calculations become more complex for individual tissue exposures vs. whole body exposures

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 95 Examination Skin dose Effective dose Risk (mGy) (mGy) (%) Urography 30 8 0.04 Lumbar spine 40 5 0.025 Abdomen 10 2.5 0.013 Chest 2 0.25 0.0013 Extremities 3 0.025 0.00013 Radiation Risks in X-RAY Examination

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 96 Examination Radiopharmaceutical Effective dose Risk (mSv) (%) Myocardium Tl-201 chloride 23 0.12 Bone Tc-99m MDP 3.6 0.018 Thyroid Tc-99m pertechnetate 1.1 0.006 Lungs Tc-99m MAA 0.9 0.005 Kidney clearance Cr-51 EDTA 0.01 0.00005 Radiation Risks in Nuclear Medicine

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 97 Average Annual Risk of Death in the UK from Industrial Accidents and from Cancers due to Radiation Work From L Collins 2000 These figures can be compared to an estimate of 1 in 17000 for 1.5 mSv/year received by radiation workers

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 98 Comparison of Radiation Worker Risks to Other Workers Mean death rate 1989 (10 -6 /y) Trade40 Manufacture60 Service40 Government90 Transport/utilities240 Construction320 Agriculture 400 Mines/quarries430 Safe industries 2 mSv/y (100 mSv over a lifetime) max permissible exposure (20 mSv/year or 1000 mSv over a lifetime max permissible exposure (20 mSv/year or 1000 mSv over a lifetime

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 99 The following activities are associated with a risk of death that is 1/1000000 10 days work in a nuclear medicine department smoking 1.4 cigarette living 2 days in a polluted city traveling 6 min in a canoe 1.5 min mountaineering traveling 480 km in a car traveling 1600 km in an airplane living 2 months together with a smoker drinking 30 cans of diet soda Risks

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 100 Expected reduction of life Unmarried man3500 days Smoking man2250 days Unmarried woman1600 days 30% overweight1300 days Cancer 980 days Construction work 300 days Car accident 207 days Accident at home 95 days Administrative work 30 days Radiological examination 6 days Risks

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 101 Questions??

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 102 Discussion A woman was referred to a bone scan. After the examination she turned out to be pregnant at a very early stage. She is extremely worried and wants to have an abortion. Discuss how to act.

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 103 Discussion Dose fractionation results in: increased radiation sensitivity for photons? decreased radiation sensitivity for photons? decreased radiation sensitivity for heavy charged particles? increased radiation sensitivity for heavy charged particles?

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 104 Discussion A patient (radiobiologist) wants to know the radiation risk he will suffer in an examination of the cerebral blood flow (1000 MBq 99m Tc). What to answer?

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Nuclear Medicine Part 1. Biological effects of ionizing radiation 105 Where to Get More Information Other sessions Part 2 Radiation Physics Further readings WHO/IAEA. Manual on Radiation Protection in Hospital and General Practice. Volume 1. Basic requirements ICRP publications (41, 60, 84) UNSCEAR reports ALPEN E.L Radiation Biophysics. Academic Press, 1998 RUSSEL, J.G.B., Diagnostic radiation, pregnancy and termination, Br. J. Radiol. 62 733 (1989) 92-3.