Transcript Environmental and Medical Radiation Exposure

Health effects of radiation
exposure
Tilman A Ruff
Nossal Institute for Global Health, University of Melbourne
Advisor: Australian Red Cross, AusAID/UNICEF
Consultant: GSK Biologicals, Novartis Vaccines
Medical Association for Prevention of War
International Campaign to Abolish Nuclear Weapons
Hunter’s Hill Inquiry, Sydney 4 July 2008
Overview
• Overview of radiation
• Sources of environmental radiation
• Health effects of radiation
Radiation Basics
Radiation – Energy in transit:
– electromagnetic waves (gamma-γ or x-ray), or
– high speed particles ( alpha-α, beta-β, neutron-η, etc.)
Ionizing Radiation – Radiation with sufficient
energy to remove electrons during interaction
with an atom, causing it to become charged or
ionized
– Can be produced by spontaneous radioactive decay or
by accelerating charged particles across an electric
potential (eg x-rays)
Introduction
• What is ‘radiation’?
– Electromagnetic energy
– Spectrum
Ionizing vs Non-ionizing
• Ionizing radiation has high energy and displaces
electrons from their orbits creating charged
atoms (ions)/molecules
–
–
–
–
Creates DNA damage
Outright cell death
Bystander effect
Genomic instability
• Non-ionizing radiation creates heat due to low
energy eg infrared, MRI
Radiation
types
Ionizing Radiation Sources
• Average global dose: 2.4 mSv
Ionizing Radiation Sources
Multiple exposure pathways
• External - often gamma
• Most easily measured
– Direct contact – skin
• Internal
– Inhale – gas, dust, aerosol
– Ingest
• Food – many radioisotopes bioconcentrated
• Water
• Environmental source esp young children
– Wounds
Radiation Basics
Radioactivity – 1 Becquerel (Bq)= 1 radioactive
disintegration per sec
Absrbed dose – 1 Gray (Gy) = 1 joule of energy
deposited per kilogram
Equivalent dose (biological effect) – Sievert
(Sv) the unit of absorbed dose equivalent. The
energy absorbed by the body based on the damaging
effect for the type of radiation.
Sv =Gray x Quality Factor
Radiation Quantities and Units
• Biological equivalent dose: Sievert (Sv) = joules
per kilogram
– Relates to the amount of radiation harm in biological
tissues
• Beta, gamma, and x-ray Sv = Gy
• Particle weightings (electrons = 1; neutrons = 5; alpha = 20)
• Biological effective dose: Sievert (Sv) =
equivalent dose weighted for susceptibility to
harm of different tissues
U-238 radioactive
decay
tissue
injury:
alphaparticle
track …
lung cells
• Produced from radium
•
•
in decay chain of
uranium
Escapes into air –
short lived decay
products emit alpha
particles – stick to
dust, inhaled, deposit
in lung – high but
localised radiation
Second most
important cause lung
cancer
Radon
Radon
• Average outdoor levels: 5-15 Bq/m3
• Global indoor average: 39 Bq/m3
• Action levels – generally 200-400 Bq/m3
•
•
•
•
(Australia 200)
Risk of lung cancer increases by 16% per 100
Bq/m3 increase in radon
Relationship linear with no threshold
Risk synergistic with smoking
Some (weak) evidence of increased effect at low
dose rate
Radon
risk per 1000 of lung cancer by age 75 y
Non-smoker
Smoker
0 Bq/m3
4
100
100 Bq/m3
5
120
400 Bq/m3
7
160
WHO Factsheet 291 June 2005
Cell Sensitivity
• Cells most affected:
– Rapidly dividing cells:
• small intestines, bone marrow, hair, fetus
Varying tissue sensitivities
Health Effects of Radiation
Ionising radiation
• Capacity to damage core
genetic blueprint - DNA
→ cancer
→ other health effects
→ genetic damage
• Lethal dose can have
equivalent energy to
heat in a cup of coffee
• Many different isotopes
• Behave differently
biologically
Biological Effects of Radiaton
• Deterministic effects (>100mSv)
– Threshold
– Increased dose = increased damage
• Stochastic (probabilistic) effects (no safe
threshold)
– Increased dose = increased probability of
damage but not severity
Delayed Somatic Effects
• 1. Cancer: solid tumors
– Increased risk
– Latency period: 10+ y
• 2. Cancer: leukemia
– Increased risk
– Latency period: 5+ y
• 3. Degenerative effects (LSS, not sure at low
doses)
– Life shortening (not sure)
– Heart disease, stroke; digestive, respiratory,
hemopoietic systems
Cancer Risks
• Normal cancer risk (Australia):
– About 1:2 men get cancer by age 85
– About 1:3 women get cancer by age 85
• Normal mortality:
– 29% of Australians die primarily from cancer
– 49.3 % die primarily or as a consequence of
cancer
Cancer in Australia: an overview 2006, AIHW
Cancer Risks
• Linear, no threshold
• Increased risk of cancer from 1 mSv of
radiation:
– Solid tumor cancer risk about 1 in 10,000
– Leukemia risk about 1 in 100,000
• Increased risk of cancer mortality about
half those :
– Solid cancer deaths: about 1 in 20,000
 BEIR
VII 2005
Cancer risks vary
• Infancy 3-4x increased risk cf 20-50y
• Female infants 2x risk of male infants
• Female risk of cancer is 37.5% greater
than males
– 50% greater risk of solid tumours
– Less risk leukaemia
 BEIR
VII 2005
Fetal radiation risk
• There are radiation-related risks throughout
•
pregnancy that are related to the stage of
pregnancy and absorbed dose
Radiation risks are most significant during
organogenesis and in the early fetal period,
somewhat less in 2nd trimester, and least in 3rd
trimester
•
Most
risk
Less
Least
Leukaemia and cancer
• The relative risk may be as high as 1.4
(40% increase over normal incidence) due
to a fetal dose of 10 mSv
• For an individual exposed in utero to 10
mSv, the absolute risk of cancer at ages 015 is about 1 excess cancer death per
1,700
Medical Radiation Exposure
Procedure
Effective
dose
(mSv)
Equivalent
CXR
EBR
(days)
Equivalent
aircraft flight
hours
Probability of fatal
cancer
Chest x-ray
(PA)
0.02
1
3
2
1:625,000
CT brain
3
150
456
300
1:4200
CT chest
8
400
1217
800
1:1600
CT abdo/pelvis
11
550
1673
1100
1:1100
CT coronary
angio
10
500
1521
1000
1:1250
Conventional
coronary angio
3-11
150
456
300
1:4200
Ba enema
8.7
435
1323
870
1:1400
mammography
0.1
5
15
10
1:125000
Nuclear
myocardial
perfusion study
12
600
1825
1200
1:1000
Nuclear bone
scan
4.4
220
669
440
1:2800
CT Scanners
CT Scanners
Nuclear industry workers 1
• 15 country retrospective cohort study of cancer mortality
•
•
•
•
auspiced by IARC
Largest such study ever conducted
Workers involved in fuel enrichment or reprocessing,
reactors, weapons or isotope production (excl uranium
mining)
407,391 workers (90% male):
– employed ≥ 1 y
– monitored for external photon (X and gamma) radiation
– > 90% whole body dose from external photons rather
than neutrons or internal exposures
Total FU 5.2 million person y
Nuclear industry workers 2
• Doses to colon used for all and solid cancer, active
bone marrow for leukemia analyses, lagged by 2 y
for leukemia and 10 y for other cancers
• Doses:
– Average 19.4 mSv
– 90% < 50 mSv
– < 0.1% > 500 mSv
• Total deaths 6516 from cancer other than leukemia,
196 from leukemia excl CLL
Nuclear industry workers 4
• Mortality from all cancers except leukemia
– central estimate 2-3 times higher than
linear extrapolation from atomic bomb
survivors
– Current recommended 5 y occup dose limit of
100 mSv → 9.7% (1.4 - 19.7%) increase in
cancer excl leukemia
– For leukemia excl CLL 100mSv → 19% (<0 84.7%) increase
Cardis E, et al. BMJ 2005 (29 June 2005)
BMJ,doi:10.1136/bmj.38499.599861.EO
‘Routine’ radiation releases
• First large meta-analysis of data on childhood
•
•
•
•
•
leukaemia and nuclear facilities
International peer-reviewed journal
Multiple sites, different populations, different time
periods, collected differently are difficult; findings
more likely to be significant
No major sources of bias identified
Countries with poorer environmental standards eg
Russia, China and developing countries are
excluded, so likely best case scenario
Effects robust to different types of analyses
‘Routine’ radiation releases
• Point estimates are all above 1
• A number of important findings are statistically
•
•
•
significant eg all of the results for childhood
leukaemia incidence
Association of young age and closeness to a
nuclear facility with higher risk are biologically
plausible, suggest dose-response effect
Heightened sensitivity of children to radiation, and
leukaemia as most radiation sensitive cancer with
shortest latent period support biological plausibility
funded by the US DOE
• German Childhood
•
•
•
Cancer Registry data
1980 – 2003, <5y
Matched case-control
study
593 leukemia cases
Odds ratio for
leukemia 2.19 (lower
95% CI 1.51) for
residence within 5 km
of nuclear power plant
• 1592 cases, 4735
•
controls
Odds ratio 1.47
(lower 95% CI 1.16)
for inner 5 km zone
Thank you!