核医学辐射防护Radiation Protection in Nuclear Medicine

RepairLeabharlann Baidu
The human body contains about 1014 cells. An absorbed dose of 1 mGy per year (natural sources) will produce about 1016 ionizations, which means 100 per cell in the body. If we assume that the mass of DNA is 1% of the mass of the cell, the result will be one ionization in the DNA-molecule in every cell in the body each year.
radiation hit cell nucleus!
DNA mutation
Outcomes after cell exposure
DNA Mutation
Mutation repaired
Viable Cell
Cell death
Unviable Cell
Cell survives but mutated
… order of magnitudes
• 999 of 1000 lesions are repaired • 999 of 1000 damaged cells die (not a major
problem as millions of cells die every day in every person)
Information comes from:
✓ studies of humans (epidemiology) ✓ studies of animals and plants (experimental
radiobiology)
✓ fundamental studies of cells and their components
(cellular and molecular biology) The key to understanding the health effects of radiation is the interaction between these sources of information.
Radiation exposure affects the center of life: the cell
First report of leukaemia in humans and lung cancer from occupational exposure
94 cases of tumour reported in Germany (50 being radiologists)
Effects of Radiation Exposure
RADIATION PROTECTION IN NUCLEAR MEDICINE
Part 1: Biological effects of ionizing radiation
OBJECTIVE
To become familiar with the mechanisms of different types of biological effects following exposure to ionizing radiation and results of epidemiological studies of exposed population to ionizing radiation. To be aware of the models used to derive risk coefficients for estimating the detriment
DNA-polymerase fills resulting gap but nick remains
DNA ligase seals the nick. Repair completed.
DNA has been repaired with no loss of genetic information
Module 1.1. Basic concepts
Early Observations of the Effects of Ionizing Radiation
• 1895 • 1896 • 1896 • 1896 • 1897 • 1902 • 1911
• 1911
X-rays discovered by Roentgen First skin burns reported First use of x-rays in the treatment of cancer Becquerel: Discovery of radioactivity First cases of skin damage reported First report of x-ray induced cancer
Chromosomes
The critical target: DNA
Interaction of ionizing radiation with DNA
DIRECT ACTION
INDIRECT ACTION
Damage to DNA
Exposure of the cell
No change
CONTENT
• Basic concepts, cellular effects • Deterministic effects • Stochastic effects • Effects on embryo and fetus • Risk estimates
Part 1. Biological effects
Cancer?
How is DNA repaired?
Altered base
Enzyme Glycosylases recognizes lesion and releases damaged base
AP-endunuclease makes incision and releases remaining sugar