Hormesis and Possible Dose Threshold for Cancer Risk

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Hormesis and Possible Dose Threshold for Cancer
Risk

• Richard Wakeford

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Dose-response Curves
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Excess relative risk (and 95 CI) of solid tumour
incidence among the Japanese atomic bomb
survivors during 1958-1987 (showing fitted
linear dose-response, and 95 CI on the slope)
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Excess relative risk (and 95 CI) of solid tumour
incidence among the Japanese atomic bomb
survivors during 1958-1987 (showing linear
dose-response fit to data for the 0-3 Sv dose
range)
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Relative Risk of Solid Tumour Incidence among the
Japanese Atomic Bomb Survivors during 1958-1994,
showing the Smoothed Fitted Curve through the Low
Dose Data plus 95 Confidence Band. The Straight
Line is the Linear Fit to the Data for the 0-2 Sv
Dose Range.
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Excess Relative Risk (and 95 CI) of Thyroid
Cancer from the Pooled Data of Five Cohort
Studies of External Irradiation in Childhood (lt15
years of age)
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Medical Diagnostic Irradiation

• Antenatal X-ray Examinations
• Evidence that fetal doses 10 mGy discernibly
  increase the risk of childhood cancer
• Chest Fluoroscopy
• Multiple fluoroscopic examinations during
  treatment of TB with artificial pneumothorax
• Large doses given in fractions of 10 mGy
• Risk of breast cancer fully additive
• Risk of lung cancer not detectably raised

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Relative Risks (and 90 CI) of Leukaemia
(excluding CLL) by Cumulative External Radiation
Dose for the UK National Registry for Radiation
Workers compared with the Japanese Atomic Bomb
Survivors
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Japanese
Japanese
5
NRRW
4
Relative Risk
3
2
1
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Dose (Sv)
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Relative Risks (and 90 CI) of All Solid Tumours
by Cumulative External Radiation Dose for the UK
National Registry for Radiation Workers compared
with the Japanese Atomic Bomb Survivors
1.50

Japanese
Japanese
NRRW
1.25
Relative Risk
1.00
0.75
0.50
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Dose (Sv)
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(No Transcript)
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Relative Risk of Lung Cancer by Cumulative
Exposure to Radon Progeny (Working Level Months,
WLM). Combined Data from Eleven Cohorts of
Underground Hard Rock Miners.
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Residential Exposure to Radon
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Dose-response Model

• there is no conclusive evidence on which to
  reject the assumption of a linear-nonthreshold
  dose-response relationship for many of the risks
  attributable to low-level ionizing radiation
• NCRP Report No. 136 (2001)

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Dose-response Model

• the probability of effects at very low doses
  such as are received from natural background is
  so small that it may never be possible to prove
  or disprove the validity of the
  linear-nonthreshold assumption
• NCRP Report No. 136 (2001)