Download Radiobiology

Radiation safety
level 5
Frits Pleiter
23/05/2017
radiation safety - level 5
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Contents
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
atomic and nuclear physics
interaction with matter
o
sources and x-ray equipment
shielding
detection
o
radiobiology
o
o
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
•
objective risk of radiation
•
subjective risk acceptation
quantities and units
regulations
o
practical health physics
o
waste
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(1)
(3)
(2)
(3)
(4)
(6)
(6)
(6)
(5)
(7)
(8 - 10)
(11)
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Radiobiology
cell
nucleus
cytoplasm
cell membrane
nucleus contains
23 pairs of
chromosomes
chromosomes carry total genetic load
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Radiobiology
DNA
chromosome = DNA-molecule
DNA = polymer of alternating suger
and a phosphate groups
suger group contains nitrogen base
A = adenine
C = cytosine
G = guanine
T = thymine
double helix structure
A-T
C-G
replication (cell division)
reparation (after damage)
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Radiobiology
DNA
gene
a gene contains the code for the synthesis of a specific protein
4 letters A, C, G and T
4  4  4 = 64 three-letter words
gene = series of three-letter words = piece of DNA
30 000 genes
protein
protein = polymer of (up to 2000) amino acids
20 different amino acids
properties of protein determined by its 3-dimensional structure
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Radiobiology
protein synthesis
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Radiobiology
from human to DNA
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Radiobiology
radiation damage
direct damage due to ionisation of biomolecules
carbonhydrate, protein, lipid, DNA, ...
tissue contains about 60% water
ionizing radiation induces free radicales H• and •OH
indirect damage by chemical reactions with biomolecules
this is the most important contribution
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Radiobiology
radiation damage
DNA is the critical molecule during cell division
a frequently dividing cell has insufficient time for repair
most radiation sensitive are stem cells and proliferating cells
bone marrow, epithelium of the intestines
least radiation sensitive are differentiated and functional cells
neuron, brains
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Radiobiology
radiation damage
time scale
process
10-18 - 10-17 s
10-16 s
10-12 - 10-7 s
seconds - minutes
minutes - hours
absorption of radiation energy
formation of primary radicals by radiolysis
reaction of radical and biomolecule
biochemical modification (enzymes)
reparation of damage
 central nervous system syndrome
cell death
 gastrointestinal syndrome
more acute effects
 bone marrow syndrome, cutaneous syndrome
late effects, cancer
genetic damage in progeny
days
days - weeks
months - years
generations
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Radiobiology
radiation damage
somatic effect
damage comes to expression in the exposed generation
genetic effect
damage comes to expression in next generations
acute effect
damage comes to expression within months
late effect
damage comes to expression after years
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Radiobiology
radiation damage
harmful tissue reaction
(deterministic effect, non-stochastic effect)
severity of the effect depends on dose
dose-effect relation shows a threshold
damage is expressed sometimes shortly after exposure (acute effect)
sometimes there is a long latency period (late effect)
stochastic effect
probability of occurrence depends on dose
severity of the effect DOES NOT DEPEND on dose
there is NO threshold
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Radiobiology
harmful tissue reaction and radiation syndrome
occurs always above a threshold dose
more severe at higher dose
LD50  3-5 Gy for total body irradiation
radiation syndrome
mortality
threshold
bone marrow syndrome
gastrointestinal syndrome
brain syndrome
cutaneous syndrome
10-30 days
4-10 days
< 2 days
1 Gy
10 Gy
50-100 Gy
brain syndrom is also called central nervous system syndrome
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Radiobiology
harmful tissue reaction and cutaneous syndrome
Gilam, Iran, July 1996
skin dose  50 Gy
body dose  4.5 Gy
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Radiobiology
harmful tissue reaction and dose-effect relation
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Radiobiology
harmful tissue reaction and cataract
probability p of occurrence of cataract for patients who have
received radiotherapy; in between the lines this probability is
0 < p < 1; below this region p = 0, above the region p = 1
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Radiobiology
harmful tissue reaction and unborn child
week 1
all-or-nothing effect: spontaneous abortion
threshold  100 mGy
week 2-8
formation of the organs (organogenesis)
radiation damage may cause malformation
week 8-15
development of the brain
radiation damage may cause a reduced IQ
threshold  100 mGy
week 16-36 development is being completed
radiation damage may cause growth retardation
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Radiobiology
stochastic effect and cancer
no threshold
effect is independent of dose (all-or-nothing effect)
very long latency period
it all begins with DNA damage
risk factor = 5% per sievert
obtained from epidemiological studies among the survivors
of the atomic bombs on Hiroshima and Nagasaki
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Radiobiology
stochastic effect and dose-effect relation
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Radiobiology
stochastic effect and latency period
minimum 3 - 5 year for leukemia
minimum 10 year for other cancers
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Radiobiology
stochastic effect and genes
(proto)oncogene enhances cancer growth
tumor suppressor (TS) gene inhibits cancer growth
oncogene cancer
N-ras
Ki-ras
c-myc
Bcl-2
Bcl-1
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TS-gene
neuroblastoma
NF-1
leukemia
lung, ovaria
NF-2
intestine, pancreas
lymphatic system
p-53
breast, stomach, lung
BRCA-1
lymphatic system
BRCA-2
breast, head, neck
VHL
radiation safety - level 5
cancer
nervous system
myeloid leukemia
brain
many cancers
breast, ovaria
breast
kidney
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Radiobiology
stochastic effect and progeny
radiation damage in gamete cells before pregnancy
sperm cell for man
egg cell for woman
sensitivity for radiation damage is not the same in the different
development stages of gamete cells
teratogene effect = risk of developing a heritable disease
is probably much smaller than generally thought
risk for unborn child and young child are about the same
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