Low Dose Radiation Risk

8/3/2019 Low Dose Radiation Risk

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Low Dose Radiation Risk

Antone Brooks

Washington State University

TriCities

5 May 2004


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My Background

Early interest in radiation(Watching atomic weapons in southern Utah)

MS in radiation ecology (Chasing fallout)

PhD in radiation biology in genetics(Trying to discover what radiation is actually doing inside people)

Investment of my life in research on healtheffects of low doses of radiation


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Risk Models

Is risk always proportional to dose?

Can any amount dose increase risk?

Can a single radioactive ionization can cause cancer?

Dose Dose

Ris

k

Linear No Threshold Non-Linear Threshold


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Dose Response

Learn from the Past

Route of Administration

Species


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Background Radiation

andBackground Cancer


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Background

Radiation


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Radiation is everywhere

We live in a sea of radiation

Cosmic

Inhaled Radon

RocksRadioactive Elements

PlantsBodies


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BACKGROUND RADIATION

The average background radiation

per person is 370 millirems(mrem) per year. This varies

widely depending on where

someone lives, and theiroccupation, health and lifestyle.


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Most background radiation is natural.

It is part of nature.

It has always been here.

People have always lived with it.



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Radiation comes from space-

sun and cosmic rays

Because this type of radiation is

somewhat shielded by the atmosphere,the dose is higher at higher altitudes.

Space and airline travel has higher

radiation doses.


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Background Radiation Exposure

at Different Elevations

0

20

40

60

80

100

120

140

Sea Level Death

Valley

Richland,

WA

Denver,

CO

Ledville,

CO

mrem/year

Every 200 feet increase in altitude increases dose 1 mrem/year

-282 Ft 427 Ft 5,280 Ft 10,157 Ft


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Radiation comes from the earth

Some rocks, like Uranium are radioactive.So are coal and some building materials such

as granite.

The natural radiation from the granite in Grand Central Station

is higher than is allowed to certify a nuclear power plant.


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Radon is a radioactive gas that

comes from inside the earth

Usually radon escapes into the air in very small

amounts and does not hurt us. However, sometimesradon can get trapped in buildings. Then there is

more radiation than is healthy.


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Cells in our body contain radioactive

elements, such as Potassium, which

come from the food we eat

Milk


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Are low levels of radiation an essential part

of life?

The body does not distinguish between

natural and man-made.

Neither natural nor man-made background

radiation have been shown to be harmful.

The body has developed repair mechanisms

to deal with negative effects of high levels

of radiation.


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About 70 mrem/yr

Medical procedures 53 mrems

Consumer products 10 mrems

One coast to coast airplane flight 2 mrems

Watching color TV 1 mrem

Sleeping with another person 1 mrem

Weapons test fallout less that 1 mrem

Nuclear industry less than 1 mrem

Normal annual exposure from man-made radiation

Normal annual exposure from natural radiation

About300 mrem/yr Radon gas 200 mrem

Human body 40 mrem

Rocks, soil 28 mrem

Cosmic rays 27 mrem


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Dose Ranges

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

0 100 200 300 400 500 600 700 800 900 1000

0 10 20 30 40 50 60 70 80 90 100

0 1 2 3 4 5 6 7 8 9 10

0 0.1 0. 2 0.3 0. 4 0. 5 0.6 0.7 0.8 0. 9 1

0 0.01 0.02 0.03 0.04 0.05 0.0 6 0.0 7 0.08 0.0 9 0.1

(mSievert)

0 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000

Cancer Radiotherapy

Experimental Radiobiology

Cancer Epidemiology

DOE Low Dose Program

Medical Diagnostics

Regulatory Standards

Total Body Therapy Total Tumor Dose

A-bomb survivors

Significant cancer risk at > 200 mSv

(UNSCEAR)

Human LD50

Typical mission dose on Int. Space Station

Typical annual dose for commercial airline flight crews

Bone (Tc-99m)Thyroid (I-123)

Chest X-ray

Dental X-ray

ICRP Negligible Dose

NRC Dose Limit for PublicNatural background

Site Decommissioning/License Termination

3-Mile Island Ave Ind

Occupational Limit NRC, EPA

EPA Clean-up Standards NRC Clean-up Standards


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Background

Cancer


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Stomach Cancer Risk

Type A

BloodSmoked

Foods

Type A

Blood

SmokingType A

Blood

Smoked

FoodsSmoking Shipyard

Type A

Blood

Smoked

Foods

Aging

Multiple factors impact cancer


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Effects of Atomic Bomb

Killed outright by the bombor acute radiation effects.

Survived for lifespan study

100,000 people

86,572 people


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Atomic Bomb Survivor

Excess Cancer

5467

Total Cancer Excess 437

Population of Survivors Studied 86,572

Total Cancers observed after the Bomb 8,180

Total Cancers Expected without Bomb 7,743

Excess Leukemia

104

Excess Tumor

334 437+ =


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Why now?

Standards have been set from high doseeffects, but low dose effects have not beenmeasurable until now

New technological developments andbiological discoveries have made it possibleto study low dose effects


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Key Research Areas

Technological Advances

Biological Advances


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Alpha-Particle Radiation System

Video Camera

Newport Positioning StageMicroscope Objective Lens

Mylar Bottom Petri Dish

Viewing Light

Scintillation Detector

Scintillation Plastic

Manually Adjustable Collimeter

Faraday Cup

Vertical Bending Magnet

Piezoelectric Shutter

Beam Control Slits

Beam from Accelerator

Texas A&M


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GenePix: scanner by Axon

2 color laserConfocal imaging

LLNL


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Relationship between biological

responses to radiation

Adaptive

Response GenomicInstability

Bystander

Effects

R di i i d d h i


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Radiation-induced changes in

gene expression

Dose (cGy)

0 10 100 1000

Low Dose

Genes

High Dose

Genes

Wyrobek


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Adaptive Response

0

1020

30

40

50

6070

80

90

0 0.5 150 0.5 + 150

Observed

Expected

Shadley and Wolff 1987

Dose cGy

When a small dose of radiation is given before a larger one, it would be

expected there would be more chromosome aberrations than when justthe large dose was given. But that is not what happens. With a smalltickle dose before the larger dose, there were only about half as many

aberrations than with just a large dose!

Intervention


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Bystander Effects

B t d Eff t


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Bystander EffectAll-or-none dose response

0

0.01

0.02

0.03

0.04

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Numbers of particles per targeted cell

One cell targeted per dish

Four cells targeted per dish

Belyakov et al. 2001

Intervention


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Radiation-induced Genetic DamageOld Paradigm

After a cell is damaged by radiation, all of its progeny aredamaged


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Genomic Instability

Genemutation Chromosomeaberration Mitotic failure-aneuploidy

Cell death Micronuclei

Intervention

G i i i C


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Normal

Initiation

Promotion

Progression

Gene Mutation and Expression in Cancer

Gene Mutation- a rare event Gene Expression- a common event

Gene Activation

Down

Regulation

Normal

Progression


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There is a need for a change in

interpreting radiation biology

Adaptive response and protective effects vsdetrimental effects

Hit theory vs. bystander effects

Mutation vs. gene induction Single cell vs tissue responses

Wh t h


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What have we

learned? High doses of radiation can produce cancer

Radiation is a good cell killer Radiation is a poor mutagen/carcinogen

Low doses of radiation produce different

cell and molecular responses than highdoses (Protective vs harmful?)

Linear extrapolation of risk is conservative

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Low Dose Radiation Risk