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IAEAInternational Atomic Energy Agency
Basics of BiodosimetryPart 1
LectureModule 2
IAEA
What is Biodosimetry?
Biodosimetry is the use of any biological change in an irradiated person that can be sufficiently quantified to indicate their radiation dose
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The ideal specification for a biological dosemeter
• Specific to radiation• Low background• Low donor variability• Low doubling dose• Dose response calibration• Persistent effect• Easy sampling• Rapid result• Cost
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What are our options?
For high doses:>2 GyProdromal nausea and vomitingDifferential white blood cell counts
Localised > 3 GyErythemaConjunctivitis
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Erythema and blistering
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Changes in neutrophil numbers after irradiation
% ofnormal
Normal
Time, d
Infections, fever, death
Critical period,infections,fever
<1
2 - 51 - 2
>5 - 6
180
100
50
00 4530
Gy
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Other possible endpoints
• Altered levels of biochemicals in body fluids• Gene mutations• Genes up- or down-regulated• Increased numbers of DNA double strand
breaks
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Our best options
Cytogenetic indicators:
• Dicentrics• Translocations• Micronuclei• Aberrations in prematurely condensed
chromosomes
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Why do we need biodosimetry ?
Doctors treat symptoms, not doses• Biodosimetry can detect false positives and
false negatives• Biodosimetry can forewarn to expect later
clinical developments• Biodosimetry can indicate partial body or
inhomogeneous exposure
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Why do we need biodosimetry?
• Dose information can inform doctors in the dose range where medical intervention is needed
• Doses <1 Gy will need no treatment, only counselling
• False alarms, i.e., no dose, need reassurance• Large events result in epidemiology follow-up
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Why do we need biodosimetry?
• Physical dosemeter badges do not necessarily reflect the wearer’s dose
• People, sometimes members of the public, who are not routinely monitored can be involved in radiation events
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Overall place of biodosimetry in radiation dose monitoring
• It supplements, but does not replace, physical monitoring
• It works for overdoses, it does not have the sensitivity of a badge
• It resolves anomalies• It helps quantify dose in the absence of
reliable physics• It relieves anxiety
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Brief early history of cytogenetic dosimetry
• Early in the 20th century it was known that radiation damages chromosomes
• 1960 breakthrough; method to visualize human chromosomes in white blood cells
• Calibrations at Oak Ridge, USA• Biodosimetry performed on mid-1960s
criticality accidents in USA
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The dicentric assay
• The first type of aberration to be used• Most frequently still used• Therefore a large body of experience• Now a routine procedure• Has been described as the biodosimetry
‘gold standard’
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A dicentric in a metaphase chromosome spread
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What is the ‘dose’ that we are measuring?
• Absorbed dose• Unit is gray (Gy)
• We relate the chromosome aberration yield to dose by reference to a dose response calibration curve in Gy
• We are measuring dose to lymphocytes• We do NOT operate in sieverts (Sv)
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What are the lymphocytes that we use
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Lymphocytes
• PHA stimulates T-lymphocytes• Lymphocytes in the blood are non-dividing• They are a synchronised population of cells
that can be stimulated to divide and can be harvested at first metaphase
• In non-dividing cells dicentrics are predominantly induced by radiation
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The lymphocyte in vitro cell cycle
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Conclusions
This lecture has described:
• Requirements for biological dosemeter
• Clinically observable effects of high doses; poorly quantitative
• Best options for more quantitative dosimetry; cytogenetics
• Why we need biodosimetry; how it helps
• Early beginnings in 1960s with the dicentric
• Consideration of dose that we specify
• Some basic points about peripheral blood lymphocyte
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