Transcript Low Dose Linearity and Hormesis for Radiation

Radiation Risks
Low Dose Linearity
Data, Science, Regulation and
Liability
Talk at Association of Physicists in Medicine
San Diego
10:00 a.m. Monday, August 11th, 2003
by
Richard Wilson
Mallinckrodt Research Professor of Physics
Harvard University
We should start with
Data
Then use theory (Science)
to fill in gaps
Decide on Aims of
Regulation
Discuss Science Policy
to meet these aims
Address implementation
DATA comes from
Societal Mistakes
Atom Bomb (RERF)
Excessive medical exposures
industrial exposures
animal data
Do they fit
environmental observations?
These were follow up to 1990.
A threshold at 0.1 Sv
(= 10 Rems) is possible
Dose was in < a second.
Less effect if dose spread in time
DRRF = 10 (animals)
3 (Techa River and Mayak)
2 NCRP and ICRP
Techa River (Kossenko);
Sr 90 dose
50 leukemias observed
102 expected from RERF
29 background
MAYAK workers
early period
(Koshurnikova)
“Leukemia” mortality
1/3.5 RERF
Could the effect at low
doses be worse than
linear?
It was so claimed for the
Hanford workers
by Mancuso Stewart and Kneale
but
Look at the DATA
Acute Effects
Characteristics
• One dose or dose accumulated in a
short time KILLS
• 1/10 the dose repeated 10 times
DOES NOT KILL
LINEARITY
AT LOW DOSES
IS USUAL!!
Walking blindfold across
Michigan Avenue
is safe: (Risk (R) = 0)
IF THERE ARE NO CARS!
The risk (R)
increases roughly in proportion
to the number of cars.
CHRONIC EFFECTS
including CANCER
Characteristics
A dose just sub-acute can give
effects if repeated.
Usually not all people affected dose response is flatter
• Low dose linearity is common
in societal risks
• Contrast Acute and Chronic
Effects
• Radiation Cancers look like
other cancers
• 30% of people get cancer
These are enough to set
LINEARITY as the DEFAULT
(but only for that cancer)
Some believe in a beneficial
effect or radiation at low doses
cf. Low doses of alcohol
reduce risk of stroke.
High doses give cancer and narcosis
This is controversial but cannot be
excluded
No one knows at low doses
Logical Steps
DATA
Scientific Interpretation:
APS/ANS/HPS/AAPM
Science policy
UNSCEAR/ICRP/NCRPM
Federal Regulators
DOD/DOE/NRC/EPA/OMB
State Regulators
Public Concern
Courts (toxic tort cases)
Plaintiff’s Bar/ALF/etc
Legitimate aims (RW)
Doses to be less than acute doses
Worker Risk comparable to other worker
risks
Public Exposure no larger than accepted
fluctuation in Background
Cost per life in all cases
$200,000 per person Sv (Public)
$2,000 per person Sv (worker)
Establish “de minimis” levels 10
(0.1Sv/yr)
Any Firm Limits enough to avoid Legal
Liability
ALARA dates from 1928
Originally:
“No one should be exposed without
expectation of benefit”
(Implicit risk-benefit analysis)
Doses must be reduced:
As Low As Practicable (ALAP)
As Low As Reasonably
Achievable (ALARA)
As Low As Reasonably
Practicable (ALARP)
(note word change without change
in understanding)
Assumed whole body dose effects (risk)
~ 1965 1 fatal cancer per 10,000 Man - Rems
~ 1991 1 fatal cancer per 2,500 Man-Rems
per 25 Person-Sv
Recommended Dose Limits (ICRP; NCRP similar)
When?
Public
Workers
~1965
500 mR/yr
5 R/yr
(expected public average 170 mR/yr)
~1991 (guidance) 100 mR/yr
5 R/yr
~ 1991
500 mR/5yr
5 R/yr
10 R/5 yr
‘91 NCRP
1R x age
Note that if a large group of workers received
the maximum, effects would just be detectable
(above background) at age 80
Conservatisms
Theory for low doses (<10 rems
in RERF)
Dose Rate Response Factor = 2
(data on leukemia says 3;
animal data range to 10)
Cost to reduce a risk used as a
minimum not a maximum
‘de Minimis” guidelines used as
regulation
Radiation Risk
should be comparable to
other Occupational Risks
Annual Risk per 100,000
Actual (av over all workers):
All Industries
7
manufacturing
3
Coal mining
24
Maximum (theory):
ICRP 5 yr av.
80
but average worker gets
about 1/5 of ICRP maximum
What Dose Parameter?
Average over 1/4 to full lifetime
Why regulate over 1/4 year?
What about contract workers?
Worker should control his exposure
Public? Liability for Lawsuits
Remember old rule: Average
over public is what matters
most
Be Prepared!
If someone sues you:
Have all data and
justification ready
Help stop frivolous
lawsuits
No. 98-56157
In the Supreme Court of the United States
JOE KENNEDY, et al. Plaintiffs-Appellants
v.
SOUTHERN CALIFORNIA EDISON COMPANY
and COMBUSTION ENGINEERING
On Writ of Certiorari to the United States Court of
Appeals for the First Circuit
BRIEF OF AMICI CURIAE
ROBERT K. ADAIR, BRUCE N. AMES, D.
ALLAN BROMLEY, PATRICIA A.
BUFFLER, BERNARD COHEN,
BERNARD GITTELMAN, SHELDON LEE
GLASHOW, MICHAEL GOUGH, RONALD
HART, DUDLEY HERSCHBACH,
LAWRENCE LITT, A. ALAN MOGHISSI,
RODNEY W. NICHOLS, ROBERT V.
POUND, NORMAN RAMSEY, JOSEPH P.
RING, FREDERICK SEITZ, EDWARD
THORNDIKE, LYNN H. VERHEY and
JAMES D. WATSON
IN SUPPORT OF DEFENDANTS-APPELLEES' MOTION FOR
REHEARING AND REHEARING EN BANC
Kennedy
worked at San Onofre Nuclear plant
Some workers brought “fuel fleas” home
Kennedy claimed his wife got Leukemia
from a fuel flea he brought home.
No evidence he brought one home
Uncontroverted evidence that the
maximum dose from the largest possible
fuel flea gave a risk of 10-7
(Probability of Causation 10-5)
3 week trial
Appeal originally allowed by 3 judge
panel.
The appeal was reversed, and the
plaintiffs blamed it on ALF!
(Where was AAPM? Health Physics
Society? NCRPM)
My website:
http://phys4.harvard.edu/~wilson/
Page on radiation references
/resource_letter.html
pages on Russian Chernobyl data
radiation/radiation_and_risk.html
Techa River
publications/pp747/techa_cor.htm
Wilson and Crouch
Risk Benefit Analysis
Riskad.html