Beyond Dose Assessment

Using Risk with Full Disclosure of Uncertainty in Public and Scientific Communication

F. Owen Hoffman, David C. Kocher and A. Iulian Apostoaei

SENES Oak Ridge, Inc.Center for Risk Analysis

102 Donner DriveOak Ridge, TN 37830

Dose Versus Risk as Assessment Endpoint

• Risk communication paradigms:

Peter Sandman

Risk = Hazard + Outrage

Hoffman et al. (2010)

Perceived risk = Estimated risk × Outrage2

• Restricting assessment to dose reduces potential for outrage, but

• Censorship of risk information leads to distrust

Consequences of Assessments Based on Dose

• Communication limited to comparisons with

– Regulatory standards

– Natural background radiation

– Doses from medical radiation

– Epidemiological limits of risk detection

• Doses associated with Lowest Observed Adverse Effects Levels (LOAELs)

• Effects of exposure cannot be compared with those from chemicals or other hazards

Disadvantages of Dose as Assessment Endpoint

• Two individuals with same dose may have markedly different risks

– Risk per unit dose depends on organ exposed, age at time of exposure, gender, attained age, and baseline risk

• Effective dose is a poor surrogate for risk

– Especially for cancers of high incidence but low mortality such as skin and thyroid

Excess Lifetime Risk (All Cancers) from 20 mSv Effective Dose

Certainty

1 in1 million

1 chancein 10

1 in100

1 in1000

1 in 10,000

1 in100,000

Acute exposure, high-energy photons, newborn female

Mean = 1.1 x 10-2

Ranges represent 95% uncertainty intervals.Stars represent mean values.

Chronic exposure high-energy photons

male at age 70

Mean = 7.8 x 10-4

Single whole-body exposureto high-energy photons

Excess Lifetime Risk (All Cancers) from 20 mSv Effective Dose

Ranges represent 95% uncertainty intervals.Stars represent mean values.whole-body exposure

Certainty

1 in1 million

1 chancein 10

1 in100

1 in1000

1 in 10,000

1 in100,000

Chronic exposure high-energy photons

male at age 70

Mean = 7.8 x 10-4

Acute x-ray exposurenewborn female

Mean = 2.7 x 10-2

Excess Lifetime Risk (Specific Cancer) from 20 mSv Effective Dose

Certainty

1 in1 million

1 chancein 10

1 in100

1 in1000

1 in 10,000

1 in100,000

Chronic dose to colon at age 20from high-energy beta emitter

(internal exposure)

Risk of Colon Cancer:Mean = 2.2 x 10-3

Acute dose to thyroid to newborn from x rays

Risk of Thyroid Cancer:Mean = 1.4 x 10-1

Ranges represent 95% uncertainty intervals.Stars represent mean values.

Female receiving dose to specified organ at specified age

The public has legitimate questions about risk from

radiation exposure;these questions deserve answers

When Addressing Questions about Risk

• Include information about uncertainty

– Uncertainty represents state of knowledge

– 95% uncertainty ranges more informative than central “best estimate” value

• Put risk estimates into perspective

– Compare with other risks

– Communicate benefits, if any

Examples of Risk Evaluations for Major Exposure Situations

• Indoor Radon

• CT scans in medicine

• Fallout from atmospheric testing of nuclear weapons

Indoor Radon- Different Ways to Express Risk

• Excess lifetime risk of death from lung cancer (never-smoker exposed to 46 Bq m-3 [1.2 pCi L-1])

– 20 chances per 10,000 (8 to 50 per 10,000)*

– 2 × 10-3 (0.8 × 10-3 to 5 × 10-3)*

– 0.2% (0.08% to 0.5%)*

– 2000 deaths per million never-smokers exposed (800 to 5000 cases per million)*

– One excess death per 500 exposed (1 per 1250 to 1 per 200 )*

* 90% uncertainty range

Indoor Radon Risk to US Population

Number of deaths in 1995 from lung cancer – 157,400 deaths in total population

• 146,400 in ever-smokers

• 11,000 in never-smokers

Fraction of lung cancer deaths due to radon– 14% (6% to 30%)* in general population

– 26% (13% to 45%)* in never-smokers

Number of deaths in 1995 from radon– 21,000 (9,000 to 50,000)*

* 90% uncertainty range

CT Scans in Medicine• Lifetime risk of cancer incidence from

abdominal scan in 50 year-old female

– 15 (6 to 35)* chances per 10,000

• Not including difference in risk between x rays and high-energy gamma rays

– 36 (7 to 110)* chances per 10,000

• Including difference in risk between x rays and high-energy gamma rays

* 95% uncertainty range

Risk to US Population from 57 million CT scans in 2007

• 29,000 (15,000 to 45,000)* excess cancers

• Not including difference in risk between x rays and high-energy gamma rays

• 60,000 (17,000 to 150,000)* excess cancers

• Including difference in risk between x rays and high-energy gamma rays

– Risk of cancer incidence would increase if non-melanoma skin cancer were included

* 95% uncertainty range

Nationwide Exposures to Iodine-131 in NTS Fallout

• Incidence of thyroid cancer in US (assuming no exposure to fallout)

– birth cohorts under age of 20 in 1952

about 400,000 cases

• Excess thyroid cancer in US from fallout

– birth cohorts under age of 20 in 1952

77,000 (13,000 to 254,000)* cases• 95% uncertainty range

Nationwide Exposures to Iodine-131 in NTS Fallout

• Probability of causation for a thyroid cancer diagnosed in later life

– Female born in 1952 who drank 1 to 3 glasses per day of fresh milk

95% uncertainty range

PC (%)City

7% to 79%36%Washington, DC

12% to 88%50%Kansas City, MO

3% to 78%28%San Francisco, CA

Probability of Causation (PC)

Placing Risk into Perspective

Challenge is to Communicate Risk to a Public Unfamiliar with Concept of

Risk Expressed as a Probability

Lifetime Risk of Cancer Incidence from Exposure to Radiation

Certainty

Indoor radon: smoker (46 Bq m-3)

Indoor radon: never-smoker (46 Bq m-3)

1 in1 million

1 chancein 10

1 in100

1 in1000

1 in 10,000

1 in100,000

* Assumes female born in 1952

Childhood exposure to 131I in NTS fallout *(thyroid dose of 0.1 Gy)

Single abdominal CT scan: 50 year-old

female

Negligible Individual Dose**

(NCRP-1993) (10 µSv/yr)

** Assumes 70-year chronic exposure

Involuntary Lifetime Risks ofCancer Incidence

Certainty

Dioxins & furans in foods

Current exposure toatmospheric fallout

(10 µGy/y)

Chromium*

Formaldehyde inindoor air

PCBs in foods

Non-smoker sharing a room with smoker (50 yrs)

1 in1 million

1 chancein 10

1 in100

1 in1000

1 in 10,000

1 in100,000

Benzene*

Vinyl Chloride*

Air pollution fromhazardous chemicals*

* outdoor air in California

What Have We Learned from Risk Assessment?

• Medical exposures now a leading source of future radiation risk to general population

– Assessments should account for

• Risk due to exposure to x rays vs. high-energy gamma rays

• Risk from incidence of non-fatal skin cancer

• Indoor radon is second leading cause of lung cancer

– May cause from 6% to 30% of lung cancers in general population

What Have We Learned from Risk Assessment?

• Thyroid cancers from childhood exposures to 131I in weapons fallout would be compensable nationwide

– If risk criteria established for compensation of energy employees were extended to public

• (i.e., upper 99th percentile of estimate of probability of causation equals or exceeds 50%)

A Vision for the Future• Radiation risk assessment embraced by regulatory

and health protection communities

• Uncertainty in risk used for decision-making

– Uncertainty represents limits to our state of knowledge about risk

– Uncertainty can include alternative hypotheses about effects at low dose

• Risk communication overcomes concern that

– Risk estimation may alarm, if not harm, an otherwise uninformed public