Nuclear Medicine

International Atomic Energy Agency Part 2: Radiation units and dose quantities Topic 1: Exposure and exposure rate

Nuclear Medicine 5 X = dQ/dm Exposure: X

Nuclear Medicine 2: Radiatio n units and dose quantiti es 6 Exposure: X The SI unit of exposure is Coulomb per kilogram [C kg-1] The former special unit of exposure was Roentgen [R] 1 R = 2.58 x 10-4 C kg-1 1 C kg-1 = 3876 R

International Atomic Energy Agency Part 2: Radiation units and dose quantities Topic 2: Absorbed dose

Nuclear Medicine 8 Absorbed dose, D The absorbed dose D, is the energy absorbed per unit mass. D = dE/dm. The SI unit of D is the Gray [Gy]. 1 Gy = J/kg. The former unit was the “rad”. 1 Gy = 100 rad.

Nuclear Medicine Part 1. Biological effects of ionizing radiation 9 Adapted from Marco Zaider (2000) IONIZATION PATTERN

International Atomic Energy Agency Part 2: Radiation units and dose quantities Topic 4: Equivalent dose H

Nuclear Medicine 2: Radiatio n units and dose quantiti es 11 Equivalent dose: H The equivalent dose H is the absorbed dose multiplied by a dimensionless radiation weighting factor, wR which expresses the biological effectiveness of a given type of radiation To avoid confusion with the absorbed dose, the SI unit of equivalent dose is called the sievert (Sv). The old unit was the “rem” 1 Sv = 100 rem

Nuclear Medicine 2: Radiatio n units and dose quantiti es 12 Radiation weighting factor, wR For most of the radiation used in medicine (X Rays, , e-) wR is = 1, so the absorbed dose and the equivalent dose are numerically equal The exceptions are: alpha particles (wR = 20) neutrons (wR = ).

Nuclear Medicine

Interaction of ionizing radiation with DNA Part 1. Biological effects of ionizing radiation 14 DIRECT ACTION INDIRECT ACTION

Nuclear Medicine Damage to DNA Part 1. Biological effects of ionizing radiation 15

Nuclear Medicine Exposure of the cell Part 1. Biological effects of ionizing radiation 16 radiation hit cell nucleus! No change DNA mutation

Nuclear Medicine Outcomes after cell exposure Part 1. Biological effects of ionizing radiation 17 DNA Mutation Cell survives but mutated Cancer? Cell death Mutation repaired Unviable Cell Viable Cell

Nuclear Medicine 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. Part 1. Biological effects of ionizing radiation 18

Nuclear Medicine RADIOSENSITIVITY Part 1. Biological effects of ionizing radiation 19 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

Nuclear Medicine BIOLOGICAL EFFECTS Part 1. Biological effects of ionizing radiation 20 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

Nuclear Medicine Part 1. Biological effects of ionizing radiation 21 Timing of events leading to radiation effects

Nuclear Medicine Biological effects of ionizing radiation Deterministic e.g. Lens opacities, skin injuries, infertility, epilation, etc Stochastic Cancer, genetic effects.

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

Nuclear Medicine Part 1. Biological effects of ionizing radiation 24 EFFECTS OF CELL DEATH EFFECTS OF CELL DEATH Dose (mSv) Probability of death D 100%

Nuclear Medicine Threshold Doses for Deterministic Effects Cataracts of the lens of the eye 2-10 Gy Permanent sterility males Gy females Gy Temporary sterility males 0.15 Gy females 0.6 Gy Part 1. Biological effects of ionizing radiation 25 dose Severity of effect threshold

Nuclear Medicine Effects in eye Eye lens is highly RS. Coagulation of proteins occur with doses greater than 2 Gy. There are 2 basic effects: Part 1. Biological effects of ionizing radiation 26 From “Atlas de Histologia...”. J. Boya Histologic view of eye: Eye lens is highly RS, moreover, it is surrounded by highly RS cuboid cells. > Visual impairment (cataract) > Detectable opacities Sv/year for many years Sv single brief exposure Effect

Nuclear Medicine Eye injuries Part 1. Biological effects of ionizing radiation 27

Nuclear Medicine Whole body response : adult Acute irradiation syndrome Part 1. Biological effects of ionizing radiation 28 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 Gy > 50 Gy Whole body clinic of a partial-body irradiation Mechanism: Neurovegetative disorder Similar to a sick feeling Quite frequent in fractionated radiotherapy

Nuclear Medicine Whole body exposure Part 1. Biological effects of ionizing radiation 29 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

Nuclear Medicine Whole body exposure Part 1. Biological effects of ionizing radiation 30 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% % 100%

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

Nuclear Medicine Delayed effects of radiation Classification: SOMATIC: they affect the health of the irradiated person. They are mainly different kinds of cancer (leukemia is the most common, with a delay period of 2-5 years, but also colon, lung, stomach cancer…) GENETIC: they affect the health of the offspring of the irradiated person. They are mutations that cause malformation of any kind (such as mongolism)

Nuclear Medicine STOCHASTIC EFFECTS OF IONIZING RADIATION Part 1. Biological effects of ionizing radiation 33

Nuclear Medicine STOCHASTIC EFFECTS OF IONIZING RADIATION Part 1. Biological effects of ionizing radiation 34 Health consequences of Chernobyl accident 1800 children diagnosed with thyroid cancer (1998)

Nuclear Medicine Genetic effects Part 1. Biological effects of ionizing radiation 35 Frequency (%) Absorbed dose (Gy)

International Atomic Energy Agency Part 1. Biological effects Module 1.4. Effects on embryo and fetus

Nuclear Medicine Part 1. Biological effects of ionizing radiation 37 PRE-IMPLANTATION

Nuclear Medicine Fetal Radiation Risk There are radiation-related risks throughout pregnancy which are related to the stage of pregnancy and absorbed dose Part 1. Biological effects of ionizing radiation 38

Nuclear Medicine Incidence of Prenatal & Neonatal Death and Abnormalities Hall, Radiobiology for the Radiologist pg 365 Part 1. Biological effects of ionizing radiation 39

Nuclear Medicine 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 Part 1. Biological effects of ionizing radiation 40 Fetal Radiation Risk

Nuclear Medicine Fetal Radiation Risk 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 Part 1. Biological effects of ionizing radiation 41 LessLeast Most risk

Nuclear Medicine Radiation-Induced Malformations Malformations have a threshold of 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 Part 1. Biological effects of ionizing radiation 42

Nuclear Medicine 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 weeks Part 1. Biological effects of ionizing radiation 43