nuclear medicine. international atomic energy agency part 2: radiation units and dose quantities...
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Nuclear Medicine
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Nuclear Medicine
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Nuclear Medicine
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International Atomic Energy Agency
Part 2: Radiation units and dose quantities
Topic 1: Exposure and exposure rate
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Nuclear Medicine 5
X = dQ/dm
Exposure: X
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Nuclear Medicine 2: Radiation units and dose quantities 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
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International Atomic Energy Agency
Part 2: Radiation units and dose quantities
Topic 2: Absorbed dose
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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.
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 9
Adapted from Marco Zaider (2000)
IONIZATION PATTERN
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International Atomic Energy Agency
Part 2: Radiation units and dose quantities
Topic 4: Equivalent dose H
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Nuclear Medicine 2: Radiation units and dose quantities 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
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Nuclear Medicine 2: Radiation units and dose quantities 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 = 5 - 20).
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Nuclear Medicine
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 14
Interaction of ionizing radiation with DNA
DIRECT ACTIONDIRECT ACTION INDIRECT ACTIONINDIRECT ACTION
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 15
Damage to DNA
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 16
Exposure of the cell
radiation hit cell
nucleus!
No change
DNA mutation
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 17
Outcomes after cell exposure
DNA Mutation
Cell survives but mutated
Cancer?
Cell death
Mutation repaired
Unviable Cell
Viable Cell
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 18
Cell killingRadiosensitivity
• 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 RS Medium RS Low RS
Bone MarrowSpleenThymusLymphatic nodesGonadsEye lensLymphocytes (exception to the RS laws)
SkinMesoderm organs (liver, heart, lungs…)
MuscleBonesNervous system
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 20
BIOLOGICAL EFFECTSDirect
effectsIndirecteffects
Cell death
Primarydamage
Modifiedcell
Damageto organ
Somaticcells
Germcells
Hereditaryeffects
CancerLeukemia
Death oforganism
Repair
Deterministiceffects
Stochasticeffects
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 21
1 0 -6
1 0 -12
1 0 -9
1 0 -15
1 0 -3
1 s e c o n d
1 h o u r
1 d ay
1 y ea r
1 0 0 y e a rs
1 m s
1 0 0
1 0 9
1 0 6
1 0 3
Energy deposition
Excitation/ionization
Initial particle tracks
Radical formation
PHYSICAL INTERACTIO NS
PHYSICO -CHEMICAL INTERACTION S
BIO LOG IC AL RESPO NSE
M EDICAL EFFECTS
Diffusion, chem ical reactions
Initial DNA damage
DNA breaks / base damage
Repair processes
Damage fixation
Cell killing
Promotion/completion
Teratogenesis
Cancer
Hereditary defects
Proliferation of "damaged" cells
Mutations/transformations/aberrations
TIM
E (
sec)
Timing of events leading to radiation effects
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Nuclear Medicine
Biological effects of ionizing radiation
• Deterministic• e.g. Lens opacities,
skin injuries, • infertility, epilation, etc
• Stochastic• Cancer, genetic
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 24
EFFECTS OF CELL DEATH
Dose (mSv)
Probability of death
D
100%
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 25
Threshold Doses for Deterministic Effects
• Cataracts of the lens of the eye 2-10 Gy
• Permanent sterility
• males 3.5-6 Gy • females 2.5-6 Gy
• Temporary sterility
• males 0.15 Gy• females 0.6 Gy
dose
Severity ofeffect
threshold
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 26
Effects in eye
• Eye lens is highly RS.• Coagulation of proteins
occur 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)
> 0.10.5-2.0Detectable opacities
Sv/year for many years
Sv single brief exposure
Effect
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 27
Eye injuries
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 28
Whole body response : adult
Acute irradiation syndrome
Chronic irradiation syndrome
Sur
viva
l tim
e
Dose
Steps:.1Prodromic
.2Latency
.3Manifestation
Lethal dose 50 / 30
BMS(bone
marrow)GIS
(gastrointestinal) 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 29
Whole body exposure
Absorbed dose (Gy)
Syndrome or 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
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 30
Whole body exposure
Absorbed dose (Gy)
Therapy Prognosis
1-10 SymptomaticTransfusions of leucocytes and platelets. Bone marrow transplantationGrowth stimu-lating factors
Excellent touncertain
10-50 Palliative Very poor
>50 Symptomatic Hopeless
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
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)
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 33
STOCHASTIC EFFECTS OF IONIZING RADIATION
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 34
STOCHASTIC 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 35
Genetic effects
Frequency)%(
10 20 30 40 Absorbed dose (Gy)
10
5
0
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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 37
PRE-IMPLANTATION
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 38
Fetal Radiation Risk
• There are radiation-related risks throughout pregnancy which are related to the stage of pregnancy and absorbed dose
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 39
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 40
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
Fetal Radiation Risk
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 41
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
Less LeastMost risk
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Nuclear Medicine Part 1. Biological effects of ionizing radiation 42
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 43
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