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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Radiation Physiology and Effects• Sources and types of space radiation!• Effects of radiation!• Shielding approaches!• Recent advances in understanding of radiation and
its affects
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© 2015 David L. Akin - All rights reserved http://spacecraft.ssl.umd.edu
Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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The Origin of a Class X1 Solar Flare
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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The Earth’s Magnetic Field
Ref: V. L. Pisacane and R. C. Moore, Fundamentals of Space Systems Oxford University Press, 1994
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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The Van Allen Radiation Belts
Ref: V. L. Pisacane and R. C. Moore, Fundamentals of Space Systems Oxford University Press, 1994
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Cross-section of Van Allen Radiation Belts
Ref: V. L. Pisacane and R. C. Moore, Fundamentals of Space Systems Oxford University Press, 1994
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Electron Flux in Low Earth Orbit
Ref: V. L. Pisacane and R. C. Moore, Fundamentals of Space Systems Oxford University Press, 1994
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Heavy Ion Flux
Ref: Neville J. Barter, ed., TRW Space Data, TRW Space and Electronics Group, 1999
Background Solar Flare
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Radiation Units• Dose D= absorbed radiation!!!
• Dose equivalent H= effective absorbed radiation!!!!!
• LET = Linear Energy Transfer <KeV/µ m>
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1 Gray = 1Joule
kg= 100 rad = 10, 000
ergs
gm
1 Sievert = 1Joule
kg= 100 rem = 10, 000
ergs
gm
H = DQ rem = RBE � rad
Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Radiation Quality Factor
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Radiation QX-rays 1
5 MeV γ-rays 0.51 MeV γ-rays 0.7
200 KeV γ-rays 1Electrons 1Protons 2-10
Neutrons 2-10α-particles 10-20
GCR 20+
Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Radiation in Free Space
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Radiation Dose vs. Orbital Altitude
Ref: Neville J. Barter, ed., TRW Space Data, TRW Space and Electronics Group, 1999
300 mil (7.6 mm) Al shielding
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Dosage Rates from Oct/Nov 2003 SPE
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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SPEs in Solar Cycles 19, 20, and 21
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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GCR Constituent Species
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Solar Max/Min GCR Proton Flux Ratio
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Radiation Damage to DNA
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Symptomology of Acute Radiation Exposure• “Radiation sickness”: headache, dizziness, malaise,
nausea, vomiting, diarrhea, lowered RBC and WBC counts, irritability, insomnia!
• 50 rem (0.5 Sv)!– Mild symptoms, mostly on first day!– ~100% survival!
• 100-200 rem (1-2 Sv)!– Increase in severity and duration!– 70% incidence of vomiting at 200 rem!– 25%-35% drop in blood cell production!– Mild bleeding, fever, and infection in 4-5 weeks
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Symptomology of Acute Radiation Exposure• 200-350 rem (2-3.5 Sv)!
– Earlier and more severe symptoms!– Moderate bleeding, fever, infection, and diarrhea at 4-5
weeks!• 350-550 rem (3.5-5.5 Sv)!
– Severe symptoms!– Severe and prolonged vomiting - electrolyte imbalances!– 50-90% mortality from damage to hematopoietic system if
untreated
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Symptomology of Acute Radiation Exposure• 550-750 rem (5.5-7.5 Sv)!
– Severe vomiting and nausea on first day!– Total destruction of blood-forming organs!– Untreated survival time 2-3 weeks!
• 750-1000 rem (7.5-10 Sv)!– Survival time ~2 weeks!– Severe nausea and vomiting over first three days!– 75% prostrate by end of first week!
• 1000-2000 rem (10-20 Sv)!– Severe nausea and vomiting in 30 minutes!
• 4500 rem (45 Sv)!– Survival time as short as 32 hrs - 100% in one week
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Long-Term Effects of Radiation Exposure• Radiation carcinogenesis!
– Function of exposure, dosage, LET of radiation!
• Radiation mutagenesis!– Mutations in offspring!– Mouse experiments show doubling in mutation rate at
15-30 rad (acute), 100 rad (chronic) exposures!
• Radiation-induced cataracts!– Observed correlation at 200 rad (acute), 550 rad (chronic)!– Evidence of low onset (25 rad) at high LET
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Radiation Carcinogenesis• Manifestations!
– Myelocytic leukemia!– Cancer of breast, lung, thyroid, and bowel!
• Latency in atomic bomb survivors!– Leukemia: mean 14 yrs, range 5-20 years!– All other cancers: mean 25 years!
• Overall marginal cancer risk!– 70-165 deaths/million people/rem/year!– 100,000 people exposed to 10 rem (acute) -> 800
additional deaths (20,000 natural cancer deaths) - 4%
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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NASA Radiation Dose Limits
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Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Density of Common Shielding Materials
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0
2
4
6
8
10
12
Polyethyle
neWate
rGr/E
p
Acrylic
s
AluminumLea
d
Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Comparative Thickness of Shields (Al=1)
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0
1
2
3
Polyethyle
neWate
rGr/E
p
Acrylic
s
AluminumLea
d
Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Comparative Mass for Shielding (Al=1)
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0
1
2
3
4
5
Polyeth
ylene
Water
Gr/Ep
Acrylics
Aluminu
mLe
ad
Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Effective Dose Based on Shielding
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Francis A. Cucinotta, Myung-Hee Y. Kim, and Lei Ren, Managing Lunar and Mars Mission Radiation Risks Part I: Cancer Risks, Uncertainties, and Shielding Effectiveness NASA/TP-2005-213164, July, 2005
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Shielding Materials Effect on GCR
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–, Human Integration Design Handbook, NASA SP-2010-3407, Jan. 2010
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Lunar Regolith Shielding for SPE
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–, Human Integration Design Handbook, NASA SP-2010-3407, Jan. 2010
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Mars Regolith Shielding Effectiveness
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–, Human Integration Design Handbook, NASA SP-2010-3407, Jan. 2010
Radiation Physiology and Effects ENAE 697 - Space Human Factors and Life Support
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Radiation Exposure Induced Deaths
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Francis A. Cucinotta, Myung-Hee Y. Kim, and Lei Ren, Managing Lunar and Mars Mission Radiation Risks Part I: Cancer Risks, Uncertainties, and Shielding Effectiveness NASA/TP-2005-213164, July, 2005
National Aeronautics and Space Administration
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!
What’s New in Space Radiation Research for Exploration?
!Francis A. Cucinotta
NASA, Lyndon B. Johnson Space Center !
Presented to Future In-‐Space Operations (FISO) May 18, 2011
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The Space Radiation Problem
Space radiation is comprised of high-‐energy protons and heavy ions (HZE’s) and secondary protons, neutrons, and heavy ions produced in shielding – Unique damage to biomolecules,
cells, and tissues occurs from HZE ions
– No human data to estimate risk – Expt. models must be applied or
developed to estimate cancer, and other risks
– Shielding has excessive costs and will not eliminate galactic cosmic rays (GCR)
!
Single HZE ions in cells And DNA breaks
Single HZE ions in photo-‐emulsions Leaving visible images
National Aeronautics and Space Administration
National Aeronautics and Space Administration
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Executive Summary
• Estimating space radiation risks carries large uncertainties that preclude setting exposure limits and evaluating many mitigation measures !
• NASA needs to close the knowledge gap on a broad-‐range of biological questions before radiation protection goals can be met for exploration !
• The Human Research Program (HRP), Space Radiation Program Element (SRP) led by JSC is committed to solving the space radiation problem for exploration
National Aeronautics and Space Administration
Space Radiation Environments
• Galactic cosmic rays (GCR) penetrating protons and heavy nuclei -‐ a biological science challenge – shielding is not effective – large biological uncertainties limits ability to
evaluate risks and effectiveness of mitigations
!• Solar Particle Events (SPE) largely medium
energy protons – a shielding, operational, and risk assessment challenge – shielding is effective; optimization needed
to reduce weight – improved understanding of radiobiology
needed to perform optimization – accurate event alert and responses is
essential for crew safety
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GCR a continuum of ionizing radiation types
Solar particle events and the 11-‐yr solar cycle
GCR Charge Number0 5 10 15 20 25 30
% C
ontr
ibut
ion
0.001
0.01
0.1
1
10
100Fluence (F)Dose = F x LETDose Eq = Dose x QF
National Aeronautics and Space Administration
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Space Safety Requirements
• Congress has chartered the National Council on Radiation Protection (NCRP) to guide Federal agencies on radiation limits and procedures – NCRP guides NASA on astronaut dose
limits • Crew safety
– limit of 3% fatal cancer risk – prevent radiation sickness during mission – new exploration requirements limit brain
and heart disease risks from space radiation
• Mission and Vehicle Requirements – shielding, dosimetry, and
countermeasures • NASA programs must follow the ALARA principle to ensure astronauts do not approach dose limits
Cell fusion caused by radiation
Fe+TGFβ
γ
TGFβ
Fe
γ +TGFβ
Sham
Space Radiation in breast cancer formation
National Aeronautics and Space Administration
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Categories of Radiation Risk
Four categories of risk of concern to NASA:
– Carcinogenesis (morbidity and mortality risk)
– Acute and Late Central Nervous System (CNS) risks
✓ immediate or late functional changes
– Chronic & Degenerative Tissue Risks
✓ cataracts, heart-‐disease, etc.
– Acute Radiation Risks – sickness or death
Differences in biological damage of heavy nuclei in space with x-‐rays, limits Earth-‐based data on health effects for space applications
– New knowledge on risks must be obtained
Lens changes in cataracts
First experiments for leukemia induction with GCR
cataracts
National Aeronautics and Space Administration
Space Radiation Health Risks
• NASA limits acceptable levels of risks of astronauts to a 3% Risk of Exposure Induced Death (REID) from cancer – PEL requirement to be below 95% Confidence Interval (C.I.) for cancer
risk protects against uncertainties in risk projection models – Estimates of number of days to be within a 95% C.I. are used to assess:
• Safe mission lengths • Crew selection criteria such as Age, Gender and Prior Exposure • Mitigations such as Shielding or Biological Countermeasure Requirements !
• Non-‐cancer risks are not well defined – Potential for late non-‐cancer mortality risks (Heart and CNS) on long-‐
term exploration missions confounds assessments of Acceptable Risk, which includes only cancer at this time
– Additionally, the NCRP recommends that limits for non-‐cancer morbidity risks be based on avoiding any clinically significant effect • Research in cells and murine models are not conclusive regarding clinical
significance of space radiation exposure to the astronaut's CNS • Need appropriate animal model to assess clinical significance
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• Retinal flashes observed by astronauts suggests single heavy nuclei can disrupt brain function. ― Central nervous system (CNS) damage by x-‐
rays is not observed except at very high doses
• In-‐flight cognitive changes and late effects similar to Alzheimer’s disease are a concern for GCR.
• NASA research in cells and mouse/rat models has increased concern for CNS Risks – Over 90 CNS journal publications supported
by NASA since 2000 – Studies have quantified rate of neuronal
degeneration, oxidative stress, apoptosis, inflammation, and changes in dopamine function related to late CNS risks
– Cognitive tests in rats/mice show detriments at doses as low as 10 mGy (1 rad)
• Large hurdle remains to establish significance in humans
Reduction in number of neurons (neurodegeneration) for increasing Iron doses in mouse hippocampus
CNS Risks from Galactic Cosmic Rays (GCR)
National Aeronautics and Space Administration
Radiation and Non-‐Cancer Effects
• Early Acute risks are very unlikely: – Low or modest dose-‐rates for SPE’s insufficient
for risk of early death – SPE doses are greatly reduced by tissue or
vehicle shielding • Radiation induced Late Non-‐Cancer risks are
well known at high doses and recently a concern at doses below 1 Sv (100 rem) – Significant Heart disease in Japanese Survivors
and several patient and Reactor Worker Studies
– Dose threshold is possible making risk unlikely for ISS Missions(<0.2 Sv) ; however a concern for Mars or lunar missions due to higher GCR and SPE dose
– Qualitative differences between GCR and gamma-‐rays are a major concern
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Control Iron NucleiVasculature Damage by GCR
NASA Space Radiation Laboratory• A $34-‐million facility, is located at DOE’s Brookhaven National Laboratory is managed by NASA’s Johnson Space Center. It is one of the few places in the world that can simulate heavy ions in space. • New joint DoE-‐NASA Electron beam injector source (EBIS) for 2009 increases space simulation capability • $9 M Annual operations cost
Beam port
RFQ Linac
EBIS SC solenoid
Dipoles – preparing
EBIS Construction
National Aeronautics and Space Administration
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Major Sources of UncertaintyNational Aeronautics and Space Administration
• Radiation quality effects on biological damage –Qualitative and quantitative differences between space radiation compared to x-‐rays or gamma-‐rays
• Dependence of risk on dose-‐rates in space – Biology of repair, cell & tissue regulation
• Predicting solar events – Temporal and size predictions
• Extrapolation from experimental data to humans • Individual radiation-‐sensitivity – Genetic, dietary and “healthy worker” effects
Durante & Cucinotta, Nature Rev. Cancer (2008)
(%) Fatal Cancer Risk0 3 6 9 12 15
Pro
babi
lity
0.000
0.003
0.006
0.009
0.012
0.015
Distribution aluminumDistribution polyethyleneDistribution Liq. Hydrogen (H2) E(alum) = 0.87 Sv E(poly) = 0.77 SvE(H2) = 0.43 SvR(alum) = 3.2 [1.0,10.5] (%)R(poly) = 2.9 [0.94, 9.2] (%)R(H2) = 1.6 [0.52, 5.1] (%)
Cucinotta et al Radiat Meas (2006)
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Space Radiation Shielding is Well Understood
Radiation Shielding Materials
August 1972 SPE and GCR Solar Min
Shielding Depth, g/cm20 5 10 15 20 25 30 35
Dos
e Eq
uiva
lent
, rem
/yr
1
10
100
1000
10000GCR L. HydrogenGCR PolyethyleneGCR GraphiteGCR AluminumGCR RegolithSPE GraphiteSPE RegolithSPE L. Hydrogen
• NASA has invested in shielding technologies for many years and understanding is nearly complete – Over 1,000 research publications since 1980 – Solar events can be shielded – GCR requires enormous mass to shield
because of high energies and secondary radiation
• Highly accurate predictive codes exist with +15% errors for organ exposure projections – Transport codes – Environmental models – Optimal materials – Topology Design methods
• Knowledge missing is accurate understanding of radiobiology for Exposure to Risk conversion
Confidence Levels for Career Risks on ISSEXAMPLE: 45-yr.-Old Males; GCR and trapped proton exposures
Solar Max
Days on ISS0
(%) C
onfid
ence
tobe
bel
ow c
aree
r lim
it
100Current Uncertainties With Uncertainty Reduction
50
60
70
80
90
250 500 750 1000 250 500 750 1000Days on ISS
Solar Max
Solar MinSolar Min
SAFE ZONE
Value Of Uncertainty Reduction Research: Cost of research to reduce uncertainties much less than cost of shielding in space or reducing mission length
National Aeronautics and Space Administration
What’s New in Space Radiation Research?
• New Epidemiology data suggests much weaker age dependence on radiation cancer risks – Number 1 Trade variable (Astronaut age) is negated
• Probabilistic risk assessments replace “rads and rem” – New Quality factors and uncertainty assessments
• Galactic cosmic rays (GCR) are much higher concern than Solar particle events – Shielding plays only a small role for GCR
• New health risks of concern from radiation – Heart disease, and Central nervous system (CNS) risks
• Risks estimated to be much smaller for “Never-‐smokers”
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Roles of Select Committees and Radiation Projection Councils
• Select expert panels from the National Academy of Sciences (NAS) and United Nations (UN) update human radio-‐epidemiology based estimates of radiation cancer risks each decade
• These reports form the basis for revised radiation protection standards and policy as recommended by the US National Council on Radiation Protection and Measurements (NCRP) and International Commission on Radiological Protection (ICRP)
• The most recent reports from NAS (BEIR VII) and the UN (UNSCEAR 2006) make important changes to the description of the age dependence of cancer risks, and cancer risks at low dose-‐rates – BEIR VII: Linear dose response with no age at exposure dependence above age 30-‐yr – UNSCEAR model shows similar age dependence for cancer incidence
• These changes will increase risk projections if accepted by NASA
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National Aeronautics and Space Administration
National Aeronautics and Space Administration
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NASA 2010 Cancer Projection Model
• NASA is developing new approaches to radiation risk assessment: – Probabilistic risk assessment
framework – Tissue specific estimates
• Research focus is on uncertainty reduction – Smaller tolerances are needed as risk
increases, with <50% uncertainty required for Mars mission
• NASA 2010 Model – Updates to Low LET Risk coefficients – Risks for Never-‐Smokers – Track Structure and Fluence based
approach to radiation quality factors • Leukemia Q lower than Solid cancer Q
National Aeronautics and Space Administration
GCR doses on Mars
National Aeronautics and Space Administration
Radiation Risks for Never-‐Smokers• More than 90% of Astronauts are never-‐
smokers and remainder are former smokers
• Smoking effects on Risk projections: – Epidemiology data confounded by possible
radiation-‐smoking interactions, and errors documenting tobacco use
– Average U.S. Population used by NCRP Reports 98 and 132
• NASA Model projects a 20 to 40-‐% risk reduction for never-‐smokers compared to U.S. Ave. – Larger decreases are possible if more were
known on Risk Transfer models – Balance between Small Cell and Non-‐Small
Cell Lung Cancer a critical question including high LET effects
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Thun et al., PLoS Med (2008)
Lung cancer in Unexposed
CDC Estimates of Smoking Attributable Cancers
Relative Risk to Never-‐smokers (NS) RR for NS to U.S. Avg
Males Current smokers Former smokers Never-‐smokers RR(NS/U.S.)
Esophagus 6.76 4.46 1 0.27
Stomach 1.96 1.47 1 0.71
Bladder 3.27 2.09 1 0.50
Oral Cavity 10.89 3.4 1 0.23
Lung* 23.26 8.7 1 0.11
Females Current smokers Former smokers Never-‐smokers RR(NS/U.S.)
Esophagus 7.75 2.79 1 0.35
Stomach 1.36 1.32 1 0.85
Bladder 2.22 1.89 1 0.65
Oral Cavity 5.08 2.29 1 0.46
Lung* 12.69 4.53 1 0.23
National Aeronautics and Space Administration
*Other cancers being considered Colon, leukemia, and liver
Point Estimates: Risk of Exposure Induced Death (REID)
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National Aeronautics and Space Administration %RE
ID per Sv
Fatal lung cancer risks per Sv (per 100 rem)Transfer model impact much larger change than >100 cm of GCR shielding– the 100 Billion Dollar question?
% REID, Females % REID, MalesAge at Exposure 35, y 45, y 55, y 35, y 45, y 55, y
Model Type Model rates Average U.S. Population, 2005Additive BEIR VII 1.20 1.20 1.18 0.65 0.66 0.66
UNSCEAR 1.28 1.27 1.22 0.71 0.71 0.69RERF 1.33 1.34 1.32 0.72 0.73 0.73
Multiplicative BEIR VII 2.88 2.74 2.38 0.95 0.92 0.83UNSCEAR 3.56 3.50 3.23 1.17 1.17 1.11RERF 3.71 4.16 4.21 1.13 1.30 1.37
Mixture BEIR VII 2.04 1.97 2.78 0.80 0.79 0.74UNSCEAR 2.43 2.39 2.23 0.94 0.94 0.89RERF 2.53 2.77 2.78 0.92 1.02 1.05
Never-smokersMultiplicative BEIR VII 0.44 0.41 0.37 0.15 0.15 0.14
UNSCEAR 0.57 0.57 0.54 0.15 0.15 0.14RERF 0.55 0.61 0.66 0.14 0.15 0.16
Mixture BEIR VII 0.85 0.84 0.81 0.40 0.40 0.38UNSCEAR 0.96 0.95 0.91 0.46 0.45 0.42RERF 0.98 1.01 1.02 0.46 0.47 0.45
Generalized Multiplicative
RERF, Generalized Multiplicative for never-smokers
0.39 0.47 0.53 0.16 0.17 0.20
National Aeronautics and Space Administration
“Safe” days in Space: Uncertainties estimated using subjective PDFs propagated using Monte-‐Carlo techniques
%REID for Males and 95% CI %REID for Females and 95% CIa Avg. U.S. Never-‐Smokers Decrease
(%)Avg. U.S. Never-‐Smokers Decrease
(%)30 2.26 [0.76, 8.11] 1.79 [0.60, 6.42] 21 3.58 [1.15, 12.9] 2.52 [0.81, 9.06] 30
40 2.10 [0.71, 7.33] 1.63 [0.55, 5.69] 22 3.23 [1.03, 11.5] 2.18 [0.70, 7.66] 33
50 1.93 [0.65, 6.75] 1.46 [0.49, 5.11] 24 2.89 [0.88, 10.2] 1.89 [0.60, 6.70] 34
a NASA 2005 NASA 2010 Avg. U.S.
NASA 2010 Never-‐Smokers
Males
35 158 140 (186) 180 (239)45 207 150 (200) 198 (263)55 302 169 (218) 229 (297)
Females
35 129 88 (120) 130 (172)45 173 97 (129) 150 (196)55 259 113 (149) 177 (231)
%REID predictions and 95% CI for never-‐smokers and average U.S. population for 1-‐year in deep space at solar minimum with 20 g/cm2 aluminum shielding:
Maximum Days in Deep Space with 95% Confidence to be below Limits (alternative quality factor errors in parenthesis):
National Aeronautics and Space Administration
Solar Min and Max Comparison with Proposed NASA Quality Factor (Q) and Tissue Weights (Wt) vs ICRP Quality Factor Definition
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Shielding Materials play little role for GCR
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MaterialE (Sv)
Solar Minimum SPE + Solar Maximum
10 g/cm2
Liquid H2 0.40 0.19Liquid CH4 0.50 0.30Polyethylene 0.52 0.33Water 0.53 0.35Epoxy 0.53 0.36Aluminum 0.57 0.43
20 g/cm2
Liquid H2 0.36 0.16Liquid CH4 0.45 0.22Polyethylene 0.47 0.24Water 0.48 0.25Epoxy 0.49 0.26Aluminum 0.53 0.30
40 g/cm2
Liquid H2 0.31 0.15Liquid CH4 0.43 0.21Polyethylene 0.46 0.23Water 0.46 0.23Epoxy 0.48 0.24Aluminum 0.51 0.26
Annual effective dose. Solar max calculations include 1972 Solar Particle Event.
National Aeronautics and Space Administration
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Solar Particle Event (SPE) Risks
National Aeronautics and Space Administration
Research studies show that risks of acute death from large SPEs has been over-‐estimated in the past: – Proper evaluation of dose-‐rates, tissue shielding, and proton biological effectiveness show risk is very small
SPE risk remain important for lunar EVA – Radiation sickness if unprotected > 2 hour EVA – Cancer risk is priority for both EVA and IVA
Proper resource management through research: – Probabilistic risk assessment tools for Lunar and Mars Architecture studies – Optimize shielding requirements by improved understanding of proton radiobiology & shielding design tools
– ESMD and SMD collaborations on research to improve SPE alert, monitoring and forecasting
– Biological countermeasure development for proton cancer, and Acute radiation syndromes (if needed)
National Aeronautics and Space Administration
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SPE Probabilistic Risk Assessment
• Using detailed data base of all SPE’s in space age (1955-‐current) and historical data on Ice-‐core nitrate samples (15th-‐century to current), SRP has developed a probabilistic model of SPE occurrence, size, and frequency – Hazard rate model using Survival
analysis – Non-‐uniform Poisson process
provides high quality fit of all SPE data
• Probabilistic model supports shielding design and resource management goals for Exploration missions
• Department of Defense model estimates various acute risks
0
20
40
60
80
100
120
140
160
2/1/54 2/1/58 2/1/62 2/1/66 2/1/70 2/1/74 2/1/78 2/1/82 2/1/86 2/1/90 2/1/94 2/1/98 2/1/02 2/1/06
Date
λ (t)
SPE Hazard Rate in Space Era
0
0.2
0.4
0.6
0.8
1
0 500 1000 1500 2000 2500 3000 3500 4000
Time, d
P ModelSample
Non-‐Uniform Poisson Process
National Aeronautics and Space Administration
Acceptable Risk Levels for Exploration Missions
• The NASA Standard of 3% Risk of Exposure Induced Death was set in 1989 by NASA Administrator with OSHA Concurrence under Code of Federal Regulation (CFR 1960)
• NASA has set an identical acceptable risk level for Exploration missions under the OCHMO’s 2006 Permissible Exposure Limits (PEL) – OSHA concurrences on NASA Health policy in Spaceflight dropped in
2004 after discussion with OCHMO • The NCRP recommendation of 3% Limit based on 3 rationales:
– Comparison of fatality rates in less-‐safe Industries made in 1989 – Comparison to risk limits for ground-‐based workers – Recognition of other spaceflight risks
• Fatality rates in less-‐safe industries have improved more than 2-‐fold since 1989 and therefore no longer valid basis; however other 2 rationale from NCRP in 1989 are still valid
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National Aeronautics and Space Administration
Acceptable Levels of Risk -‐ continued
• A discussion of higher or lower Acceptable Risk Levels would consider – Over arching Ethical and Safety standards at NASA and in the U.S. – Benefits to Human-‐kind from Exploration missions – Emerging information on possible radiation mortality risks from non-‐
cancer diseases, notably Heart (Stroke and Coronary Heart Disease) and Central Nervous System risks
– The resulting burden for morbidity risks including cancer, cataracts, aging, and other diseases that entail pain, suffering, and economic impacts • Radiation cancer incidence probability approximately Two times higher than cancer death
probability
– Improvements in other areas of safety at NASA, other government agencies and work places since 1989
– Balance between other space flight risks and space radiation risks • NCRP Recommendation is the high risk nature of space missions precludes allowing an
overly large radiation risk to Astronauts
– Impacts on finding solutions through research programs and mission design architectures that result from Acceptable Risk Standards
27
National Aeronautics and Space Administration
28
3% Risk (REID)
6% Risk (REID)
95% CL 90% CL 95% CL 90% CL
Age, y Males
35 140 184 290 36145 150 196 311 392
55 169 219 349 439
Age, y Females
35 88 116 187 232
45 97 128 206 255
55 113 146 234 293
Number of Days in Deep Space At Solar minimum with a 95% or 90% CL to be below 3% or 6% Risk of Cancer Death from Space Radiation (Avg US pop)
3% and 6% Cancer Mortality Risks at 90% to 95% Confidence Levels (CL) (Solar Min at 20 g/cm2 Aluminum)