Nuclear Medicine Nuclear Medicine Nuclear Medicine International Atomic

Nuclear Medicine

Nuclear Medicine

Nuclear Medicine

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

Exposure: X X = d. Q/dm Nuclear Medicine 5

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 Nuclear Medicine 2: Radiatio n units and dose quantiti 6

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

Absorbed dose, D • The absorbed dose D, is the energy • • • absorbed per unit mass. D = d. E/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 8

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

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

Equivalent dose: H • The equivalent dose H is the absorbed • • dose multiplied by a dimensionless radiation weighting factor, w. R 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 11

Radiation weighting factor, w. R • For most of the radiation used in • medicine (X Rays, , e-) w. R is = 1, so the absorbed dose and the equivalent dose are numerically equal The exceptions are: • alpha particles (w. R = 20) • neutrons (w. R = 5 - 20). Nuclear Medicine 2: Radiatio n units and dose quantiti 12

Nuclear Medicine

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

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

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

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

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

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

BIOLOGICAL EFFECTS Direct effects Indirect effects Repair Primary damage Modified cell Cell death Damage to organ Somatic cells Germ cells Death of organism Cancer Leukemia Hereditary effects Deterministic effects Nuclear Medicine Stochastic effects Part 1. Biological effects of ionizing radiation 20

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

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

International Atomic Energy Agency Part 1. Biological effects Module 1. 2. Deterministic effects

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

Threshold Doses for Deterministic Effects • Cataracts of the lens of the eye 2 -10 Gy • Permanent sterility Severity of • males • females 3. 5 -6 Gy 2. 5 -6 Gy • males • females 0. 15 Gy 0. 6 Gy effect • Temporary sterility dose threshold Nuclear Medicine Part 1. Biological effects of ionizing radiation 25

Effects in eye Histologic view of eye: • • • From “Atlas de Histologia. . . ”. J. Boya Eye lens is highly RS, moreover, it is surrounded by highly RS cuboid cells. Nuclear Medicine Eye lens is highly RS. Coagulation of proteins occur with doses greater than 2 Gy. There are 2 basic effects: Effect Sv single brief exposure Detectable opacities 0. 5 -2. 0 > 0. 1 5. 0 > 0. 15 Visual impairment (cataract) Part 1. Biological effects of ionizing radiation Sv/year for many years 26

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

Whole body response : adult Acute irradiation syndrome 1 -10 Gy Steps: Survival time 10 -50 Gy Prodromic. 1 > 50 Gy Latency. 2 BMS (bone marrow) GIS (gastro intestinal) CNS Whole body clinic • of a partial-body irradiation Manifestation. 3 Mechanism: • Neurovegetative disorder Lethal dose 50 / 30 Similar to a sick • feeling (central nervous system) Dose Nuclear Medicine Chronic irradiation syndrome Quite frequent in • fractionated radiotherapy Part 1. Biological effects of ionizing radiation 28

Whole body exposure Nuclear Medicine Absorbed dose Syndrome or (Gy) tissue involved Symptoms 1 -10 Bone marrow syndrome Leucopenia, thrombopenia, hemorrhage, infections 10 -50 Gastrointestinal Diarrhoea, fever, electrolytic imbalance >50 Central nervous syndrome Cramps, tremor, ataxia, lethargy, impaired vision, coma Part 1. Biological effects of ionizing radiation 29

Whole body exposure Absorbed dose (Gy) Therapy 1 -10 Symptomatic Excellent to Transfusions of uncertain leucocytes and platelets. Bone marrow transplantation Growth stimulating factors 0 -90% 10 -50 Palliative Very poor 90 -100% >50 Symptomatic Hopeless 100% Nuclear Medicine Prognosis Part 1. Biological effects of ionizing radiation Lethality 30

International Atomic Energy Agency Part 1. Biological effects Module 1. 3. Stochastic effects

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 Nuclear Medicine Part 1. Biological effects of ionizing radiation 33

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

Genetic effects Frequency (%) 10 5 0 10 20 30 40 Absorbed dose (Gy) Nuclear Medicine Part 1. Biological effects of ionizing radiation 35

International Atomic Energy Agency Part 1. Biological effects Module 1. 4. Effects on embryo and fetus

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

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

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

Fetal Radiation Risk Pre-implant stage (up to 10 days) ê Only lethal effect, all or none ê Embryo contains only few cells which are not specialized ê If too many cell are damaged-embryo is resorbed ê If only few killed-remaining pluripotent cells replace the cells loss within few cell divisions ê Atomic Bomb survivors - high incidence of both - normal birth and spontaneous abortion Nuclear Medicine Part 1. Biological effects of ionizing radiation 40

Fetal Radiation Risk • Radiation risks are most significant during organogenesis and in the early fetal period somewhat less in the 2 nd trimester and least in the third trimester Most risk Nuclear Medicine Less Least Part 1. Biological effects of ionizing radiation 41

Radiation-Induced Malformations • Malformations have a threshold of 100 -200 • • m. Gy or higher and are typically associated with central nervous system problems Fetal doses of 100 m. Gy 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 Nuclear Medicine Part 1. Biological effects of ionizing radiation 42

Central Nervous System Effects • During 8 -25 weeks post-conception the • • CNS is particularly sensitive to radiation Fetal doses in excess of 100 m. Gy can result in some reduction of IQ (intelligence quotient) Fetal doses in the range of 1000 m. Gy can result in severe mental retardation particularly during 8 -15 weeks and to a lesser extent at 16 -25 weeks Nuclear Medicine Part 1. Biological effects of ionizing radiation 43