Radiation safety - level 5

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Radiation safety - level 5

• Frits Pleiter

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Contents

• atomic and nuclear physics (1)
• interaction with matter (3)
• sources and x-ray equipment (2)
• shielding (3)
• detection (4)
• radiobiology (6)
• objective risk of radiation (6)
• subjective risk acceptation (6)
• quantities and units (5)
• regulations (7)
• practical health physics (8 - 10)
• waste (11)

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Radiobiology

• cell
• nucleus
• cytoplasm
• cell membrane
• nucleus contains
• 23 pairs of
• chromosomes
• each chromosome
• carries part of the
• total genetic load

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Radiobiology

• DNA
• chromosome DNA-molecule
• DNA polymer of alternating suger and a
  phosphate groups
• suger group contains a N-base
• A adenine
• C cytosine
• G guanine
• T thymine
• double helix structure
• A - T
• C - G
• replication and damage reparation with the aid of
  enzymes

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Radiobiology

• 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
• 105 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
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Radiobiology

• radiation damage
• direct damage due to ionisation of biomolecules
• (carbonhydrate, protein, lipid, DNA, ...)
• tissue contains about 60 water
• ionising radiation induces free radicales H and
  OH
• indirect damage by chemical reaction between
  radical and biomolecule
• DNA is the critical molecule if a cell divides
• a frequently dividing cell has insufficient time
  for repair
• most sensitive to radiation damage are stem cells
  and proliferating cells
• (bone marrow, epithelium of the intestines)
• least sensitive to radiation damage are
  differentiated and functional cells
• (neuron, brain)

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Radiobiology

• time scale process
• 10-18 - 10-17 s absorption of radiation energy
• 10-16 s formation of primary radicals by
  radiolysis
• 10-12 - 10-7 s reaction of radical and
  biomolecule
• seconds - minutes biochemical modification
  (enzymes)
• minutes - hours reparation of damage, central
  nervous system syndrome
• days cell death, gastrointestinal syndrome
• days - weeks more acute effects, bone marrow
  syndrome, cutaneous syndrome
• months - years late effects, cancer
• generations genetic damage in progeny

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Radiobiology

• radiation damage categories
• somatic and genetic effects
• Somatic effects come to expression in the
  generation that received
• the radiation dose. Genetic effects show up in
  the next generations.
• acute and late effects
• Acute or early effects show up within months
  after the irradiation.
• Otherwise we call them late effects.
• deterministic and stochastic effects
• Characteristics of deterministic effects
• there exists a threshold dose below which the
  effect does not occur
• the severity of a deterministic effect depends on
  the received dose
• they may express themselves after a short time
  (acute effect), but also after a long period of
  time (late effect)
• Characteristics of stochastic effects
• there is no threshold dose
• severity is independent of the absorbed dose
• the probabilty of occurrence depends on the
  received dose

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Radiobiology

• deterministic effect radiation syndrome
• occurs always above a threshold dose
• more severe at higher dose
• LD50 ? 3-5 Gy is for total body irradiation
• radiation syndrome mortality threshold dose
• bone marrow syndrome 10-30 days 1 Gy
• gastrointestinal syndrome 4-10 days 10 Gy
• central nervous system syndrome lt 2 days 50-100
  Gy
• cutaneous syndrome

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Radiobiology

• dose-effect relation

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Radiobiology

• deterministic effect cataract

• Probability p of occurrence of cataract for
  patients who have
• received radiotherapy. In between the lines this
  probability is
• 0 lt p lt 1. Below this region p 0, above the
  region p 1.

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Radiobiology

• deterministic effect 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 8-15development 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 cancer
• no threshold
• effect is independent of dose (all-or-nothing
  effect)
• very long latency period
• it all begins with DNA modification
• point mutation (modification of a gene)
• insertion and deletion (piece of DNA is added or
  removed)
• inversion (piece of DNA is moved)
• 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

• dose-effect relation

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Radiobiology

• stochastic effect latency period
• minimum 3 - 5 year for leukemia
• minimum 10 year for other cancers

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Radiobiology

• stochastic effect genes
• (proto)oncogene enhances cancer growth
• tumor suppressor gene inhibits cancer growth
• oncogene cancer tumor supressor gene cancer
• N-ras neuroblastoma NF-1 nervous system
• leukemia myeloid leukemia
• Ki-ras lung, ovaria NF-2 brain
• intestine, pancreas
• c-myc lymphatic system p-53 many cancers
• breast, stomach, lung
• BRCA-1 breast, ovaria
• Bcl-2 lymphatic system BRCA-2 breast
• Bcl-1 breast, head, neck VHL kidney

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Radiobiology

• stochastic effect 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
• risk of developing a heritable disease
  (teratogene effect) is probably
• much smaller than generally thought
• risk for unborn child and young child about the
  same