Low Dose Effects

RADIATION

Radiation

later

Matter

15 billionyrs

1895

X-rays

WilhelmRöntgen

A.Becquerel

M. Curie

1898Radioactivity

Radiation is everywhere

We live in a sea of radiation…

Cosmic

Inhaled Radon

RocksRadioactive Elements

PlantsBodies

Life on Earth : 4 billion years

DNA damage

Oxidative stress

- Naturalmetabolismradicals

- Externalchemicalradiation

DNA RepairBasic mechanism living cells

Enormous intensity10 per second per cell10 x 50.1012

500 billion/second

500.000.000.000.000

Incomplete or erroneous repair of DNA damage

misrepair

leads to mutations

→ defects/diseases

→ evolution / life

→ cancer

When repair mechanisms are overrun

→ DNA destruction

→ CELL DEATH

Radiationdose

UNITS

1 Gray (Gy) = 1 Sievert (Sv)Gy x Q

100 RAD 100 REM

Sv used fortotal body doseradioprotection

Doses

1Sv = 100rem

1mSv = 0.1 rem100 mrem

10 mSv = 1 rem(1000 mrem)

100 mSv = 10 rem/rad

1000 mSv = 1Sv,1Gy100 rem/rad

General population: 1 mSv / year

Professional exposure: 20 mSv / year

Permitted annual additional doseabove background

SOURCES OF BACKGROUND RADIATION IN BELGIUM

Isotopes in bodyThoronRadonNuclear energyMedicalCosmicEarth/Buildings

Total average dose in Belgium: 4.3 mSv / year

Ref RUG

Average doses from natural radiation sourcesSource: Based on Green et al, 1993

Regions with high / very highbackground

2 - 4 mSv/y France (Massif Central)6 - 7 mSv/y Finland-Sweden

>30 mSv:Ramsar, Iran: 260 mSvKerala, India: 35 mSvGuarapari, Brasil 35 mSv

High mountains 0.6 – 6 mSv/year

Transcontinental flights

0.1 mSv America0.25 mSv Australia

Smoke (one pack/day)

20 to 80 mSv per year

Doses diagnosticsRadiology

Thorax 0.02 tot 0.1 mSvBarium investigation 3 à 10 mSvCT brain 2 mSvCT abdomen/thorax 10 mSv

ref. fda.gov

Nuclear medicine

average 4.6 mSv

Bone scan 3 mSvPET-scan 7 mSv

ref.hps.org

Doses thyroidDiagnosis

Thyroid gland: Iodine 123: 100 mSvIodine 131: 1000 mSv

Total body (I131) 4 to 10 mSvTherapy

- Hyperthyroidism(usually 10 mCi) thyroid gland: 5 à 15… Sv

total body 20 to 100… mSv

- Cancer (per dose of 100 mCi) thyroid gland/tissue : 50 à 150… Svtotal body 400 to 1500… mSv

(high doses may disappear slower per unit of dose)

Dose Effects

EffectsAcute exposure >>> effective than chronicalPart of body ≠ total body irradiation

Part of body (radiotherapy)20-100 Gy (20 000 to 100 000 mSv)

Total body irradiation (TBI)in therapy (with bone marrowtransplantation)

8 to 10 Gy ( 8000 – 10 000 mSv)

Acute effects TBIClinical / hematological

– Under 250 mSv nihil

– 250 – 1000 mSv decrease white blood cells

– 1000 – 2000 mSv strong decrease blood elements

– 2000 – 5000 mSv death by marrow depression

– Above 6000 mSv death by gut mucosa necrosis

– Above 10 000 mSv no recuperation possible

“Deterministic” effects

- in all irradiated subjects- skin, mucosae, organs

bone marrow …- from treshold dose 250 mSv- severity depends on organ/dose

A) results acute (deterministic) reactions

B) “stochastic” ( random/probabilistic effects) cancer / genetic abnormalities

- all or-nothing effects

- probability increases with dose(not severity)

- very low dose possibly harmfull

Chronic, late effects

STOCHASTIC EFFECTSWell known above 100 to 200 mSv

Increase of already high incidences:only statistically evaluable

• Cancer (data Japan, accidents, after radiology/therapy …)

spontaneous incidence 33 to 50 %

• Congenital defects (dataJapan, …)

spontaneous incidence 3 % defects at birth8 to 10% genetic defects

Under 100 mSvvery controversial

Legal maxima in Belgium1 mSv population/pregnants

20 mSv professionally exposed

Why so strict?

Under 100 mSv

LNT (Linear no treshold)

vs.

Treshold hormesis?

Heavy debate

Ref.illusration: web Berkeley Nuc science:lbl.gov

Extrapolation

Working hypothesis ICRP (International Commission for Radiation Protection)

“every doseis potentially harmful”

illustration:ref uic.com

.01 .05 .1 101.0 4.0 100

The “Gold Standard” --A-bomb Survivors

5-10% Cancer Risk

Low Dose Extrapolations

Dose (Sv)(from Hall)DOE Low Dose Program

• Epidemiological models use human population exposures and outcomes

• Models confirmed to an extent by animal research

• Molecular and cellular data are not fully utilized

Radiation protection standards are currently based on human exposure data

(LNT: a testable hypothesis)

Effects according to extrapolation model(“linear” scenario- ref ICRP)

On cancer incidence: 0.6 % per 100 mSv

1 in 17 000/mSv, or “8501 i.s.8500…”

On congenital defects: not under 100 mSv

above 100-200 mSv

probability x 2 per 1000 mSv

Guidelines pregnant womenICRP

• Under 100 mSvno action

• 100-200 mSvgrey zone

• Above 200 mSvindividual counseling

Ref.ICRP pub 84

mGy=mSv

Controversial dataEpidemiologic

Cancer incidence not increased in regionswith high background

Cancer incidence lowerlow dose irradiated persons Japanin “mountain states” U S

U S dose ratesbackground

Cancer mortality

Effects low dose ControversyEpidemiologic data

Cancer incidence not increased in regionswith high background

Cancer incidence lowerlow dose irradiated persons Japanin “mountain states” VSirradiated persons in Taiwan/Ural

Longer life/lower mortality in low doseirradiated (Japan)

Effects low dose-controversialExperimental- cell biology

“Unorthodox data”Adaptive response

low dose induced

Adaptive Response

0102030405060708090

0 0.5 150 0.5 + 150

ObservedExpected

Shadley and Wolff 1987

Abe

rrat

ions

Dose cGy

Intervention

Effects low dose-controversialExperimental- cell biology

“Unorthodox data”Adaptive response

low dose inducedBystander effect

other than hit cells show- mutation- genome instability- cell death

“Cancer is a problem of cell interaction”

Effects low doseRole Tissue

- more efficiënt DNA-repair

- apoptosis harmed cells

- inhibition stable mutants

Effects of doses up to 100 mSv on top of background are

- too small to be demonstrated bystatistical methods (LNT)

or

- not existent up to a treshold(T)

Maurice Tubiana

…prevailing assumption … any dose… possibility of risk …

… there is no scientific evidence of risk at doses below about 50 millisieverts in a short time or about 100 millisieverts per year.

At lower doses and dose rates, up to at least 10 millisieverts per year, the evidence suggeststhat beneficial effects are as likely as adverse ones.

Eric Hall

Discussion on effects low doses

Enormous financial and economicalconsequences

Radioprotection is a science in crisis

Media “awareness”

1974-1978 New York Times

50 items on industrial accidents

12 000 deaths (240 /item)

200 items on nuclear incidents

0 deaths

Chernobyl

Doses : - at start: workers on reactor order of Sv, up to 2028 deaths acute, 19 later

- later on reactor: thousands of workersdoses a few hundreds of mSv

- contaminated region: 10 tot 50 mSv

Thyroid doses up to 50 Gy by drinking of contaminatedmilk

4000 cases of cancer, children and adolescents; 16deaths

Influence on other cancers: unknown, probablyimpossible to distinguish

LNT is a safety norm, not a prediction method

Risk of dying 1 per million/year

- 90 km driving- 2500 km train- 4000 km flying- 3 hrs work on fishing boat- 1.5 hrs skiing- 6 min canoeing- 1.5 cigarette- 2 days New York (air)- 33 hrs at home

or once 1 mSv

We

know

much

better…