Biological consequences of ionizing radiation BNEN 2012-2013 Intro William D’haeseleer.
-
Upload
magnus-hunter -
Category
Documents
-
view
218 -
download
0
Transcript of Biological consequences of ionizing radiation BNEN 2012-2013 Intro William D’haeseleer.
Biological consequences of ionizing radiation
BNEN 2012-2013 Intro
William D’haeseleer
Prologue (1)
• From Chemical context (Cfr P. Pôlet)
To illustrate this, I wish to tell the following anecdote.A British scientist had written a study about risks. His study had the correct inclination: he said that it is not the product, but the dose that makes the poison. The thesis of the British scientist was that you could blame every product if you only use the “appropriate” arguments. He wanted to test this and towards that purpose, he interviewed 123 at random in the London underground stations. His question was:
Prologue (2)
• From Chemical context (Cfr P. Pôlet)
Prologue (3)
• From Chemical context (Cfr P. Pôlet)
You certainly have understood this: indeed, he was talking about … . Well, about 5% said no, 19% said that they did not know, but 76% (>3/4) agreed to ban ! Unbelievable, but true. It shows the serious challenge the chemical industry is up to to improve its image and to overcome this sort of phobia.
Prologue (3)
• From Chemical context (Cfr P. Pôlet)
You certainly have understood this: indeed, he was talking about … . Well, about 5% said no, 19% said that they did not know, but 76% (>3/4) agreed to ban water ! Unbelievable, but true. It shows the serious challenge the chemical industry is up to to improve its image and to overcome this sort of phobia.
Back to
Radioactivity Radioactivity
& &
Ionizing RadiationIonizing Radiation
Ionizing particles Recall
• Directly ionizing particlesalpha (He-4++) & beta (e-/e+)
• Indirectly ionizing particlesGamma or X rays/photons & neutrons
Impact ionizing particles
• How dangerous is radiation? Cfr. B.L. Cohen:
Health impact ionized radiation …eh?
«When one of these particles or rays goes crashing through some material, it collides violently with atoms or molecules along the way…. In the delicately balanced economy of the cell, this sudden disruption can be disastrous. The individual cell may die; it may recover. But if it does recover… after the passage of weeks, months or years, it may begin to proliferate wildly in the uncontrolled growth we call cancer.»
Ref: S. Novic, “The careless atom”, Dell, NY, 1969
Impact ionizing particles
• B.L. Cohen continued:
Impact ionizing particles
• B.L. Cohen still continued:
Impact ionizing particles
Indeed, due to natural radiation:
number of e/i pairs in person 70 kg~ 109 = 1 billion per second
x 60 years (taking into account weight evolution 020y)
~ 1 à 2 1018 ionizations over one’s whole life = one billion times one billion !
How come we don’t all die like flies???
External radiation / Contamination
Fundamental difference between
External (ir)radiation
and
Contamination
Radioactive source Radioactive source outsideoutside body body
Radioactive source Radioactive source insideinside body body
External radiation / Contamination
• External (ir)radiation
External radiation / Contamination
• External (ir)radiation
- depends on type of radiation α β γ n
- shielding* natural: air / water / soil
* engineered: concrete, Pb
- distance
- irradiation time
External radiation / Contamination
• ContaminationEspecially for α & β sources !When inside the body, not possible to shield
α can cause considerable damageβ relatively dangerous
Contamination of the skin: “whipe” / “scrub” clean
External radiation / Contamination
• ContaminationNow also biological T1/2
time to remove half of radioisotope from body urine, stools, sweating, exhaling,…, vomiting,…
Effective T1/2 λeff = λph + λbio 1/Teff = 1/Tph + 1/Tbio
Smallest T1/2 dominates Teff
Special Characteristics
• Note the passive nature of radio-isotopes– Do not have “legs” do not migrate actively– Can only migrate passively must be
transported away by carrier (e.g., dissolved,…)
• Because of ionizations– Ionizing radiation (as a rule) well measurable
(compared to e.g., chemical / toxic substances)
Dose Concepts
Units & Radiation Concepts
• Recall Activity [=] Bq
Source characteristic
# disintegrations/sec
Units & Radiation Concepts
• Flux or Intensity or “exposure”[=] #/(sm2)
Field characteristic
# particles/(sm2)
Units & Radiation Concepts
• Absorbed Dose [=] J/kg or Gy
Receiver characteristic
Energy/mass
Joule/kg
Old unit rad; 1 Gy = 100 rad
Units & Radiation Concepts
• Dose Equivalent [=] Sv
Receiver characteristic in man
Energy/mass
Weighted for distribution deposited energy & biological damage
Old unit rem; 1 Sv = 100 rem
Units & Radiation Concepts
• Dose Equivalent [=] SvReceiver characteristic in man (for LL radiation)
*
*i i
i
Dose eq Abs Dose Quality Factor
D D Q
D D Q
(Sometimes correction factor for dose rate or fractionation N)
Q = 1 for X, gamma and Beta
Q = 20 for alphas
Q = 5 – 20 for neutrons (dependent upon energy)
Units & Radiation Concepts
• Collective Dose Equivalent [=] man-SvReceiver characteristic in men/women for populations (LL radiation)
1 Man-Sv = 1000 people at 1 mSv
= 100 people at 10 mSv
Only makes sense in linear relationship Dose & Effect
Careful for very small Doses & very large populations 0 x ∞ = unstable
Biological effects
• Physiology of man
Biological effects
• Cell Biology
Biological effects
• Possible biological consequences
Ionizations … free radicals … upset chemical bonds … potential damage cell… perhaps biological damage
29
Biological effects
• Interactions of radiation with cells: 4 stages
Initial physical stadium
Energy deposition & ionization
E.g., H2O → H2O+ + e-
30
Biological effects
• Interactions of radiation with cells: 4 stages
Physico-chemical stadium
Interaction ions with H2O new products
E.g., H2O+ → H+ + OH
H2O + e- → H2O-
H2O- → H + OH-
Ions H2O- H2O+ H+ OH-
Free radicals OH H
Nuclear Energy 2011-2012William D’haeseleer
31
Biological effects
• Interactions of radiation with cells: 4 stages
Chemical stadium
(some seconds)
Reaction products interact with organic molecules in the cell
Nuclear Energy 2011-2012William D’haeseleer
32
Biological effects
• Interactions of radiation with cells: 4 stages
Chemical stadium
(some seconds)
Reaction products interact with organic molecules in the cell
-Death of cell
-Impairing cell division
-Change (in nucleus of cell) transferred to daughter cells
Biological stadiumminutes - years
33
Biological effects
• Reference for more detail:
Biologic effects of radiation
1) Somatic effects (own-body related)a) Early effects due to acute high doses
= “deterministic effects”
b) Stochastic effects due to low doses
~ cancer development
2) Genetic effects (offspring-related)Stochastic in nature
Biologic effects of radiation
1) Somatic effects (own-body related)a) Early effects due to acute high doses
= “deterministic effects”
b) Stochastic effects due to low doses
~ cancer development
2) Genetic effects (offspring-related)Stochastic in nature
Deterministic effects
• Due to acute & high dose radiation• Basically accidental situation• Appears after some hours to some weeks• Because depletion of cells in important
organs (death cell / impairing cell division)• Organs such as
– bone marrow– digestive track– brains
37
Deterministic effects
• Major characteristics of deterministic effects:
1. There is a threshold of dose below which the effects will not be observed.
2. Above this threshold, the magnitude of the effect (= “severity”) increases with dose.
3. The effect is clearly associated with the radiation exposure.
Ref: Stabin, 2008
Deterministic effects
• Dose ~ 1 Gy radiation sickness• Dose < 1.5 Gy probab no early death• Dose ~ 2 Gy could lead to death after 2 wks• 30LD50 ~ 3-4 Gy (or …5 with med care) for man
deadly dose for 50% of exposed people within 30 days
• Dose 3 - 10 Gy infection death• Above 10 Gy death after 3 à 5 days• Still higher doses: CNS death
Biologic effects of radiation
1) Somatic effects (own-body related)a) Early effects due to acute high doses
= “deterministic effects”
b) Stochastic effects due to low doses
~ cancer development
2) Genetic effects (offspring-related)Stochastic in nature
Stochastic Somatic effects
• After certain weighting period can lead to cancer (solid cancers / leukemia)
• Based on observation of– Atom bomb survivors– Radiologists– Radiation therapy patients– Uranium mine workers etc
• Based on radiobiological research
Stochastic Somatic effects
• Actually extrapolation from ~ medium & high level doses
• Effects below ~ 100 à 200 mSv limited statistical significance
• Difficulty to estimate risk:– Long & variable waiting period (5…30y or more)
– Radiation-driven cancers indistinguishable from other cancers
– Human tests/experiments not justified– Animal tests/experiments not directly transferable to
humans
Stochastic Somatic effects
Curves for individual
Probability to get malignant/lethal cancer = f (dose equivalent)
LNT hypothesis
Stochastic Somatic effects
• Existence “adaptive response” & hormesis recognized, but insufficient exact justification to form basis for norms & standards
• For low doses, also dose rate is important: correction factor
DDREF: Dose & Dose Rate Effect Factor
Stochastic Somatic effects
Slope of LNT line:
~ 5 % per Sv
~ 5 x 10-5 per mSv
or
105 people with 1 mSv 5 radiation induced cancers
Stochastic Somatic effects
BEIR VII
2006
Nuclear Energy 2011-2012William D’haeseleer
46
Stochastic Somatic effects
BEIR VII 2007
Number of cases or deaths per 100,000 exposed persons
5 - 7 x 10-5 per mSv fatal cancers (solid & leukemia) DDREF= 1.5
deaths
Nuclear Energy 2011-2012William D’haeseleer
47
Stochastic Somatic effects
• LNT disputed…by some authoritative scientists…
• Considered to be
an overestimate
Nuclear Energy 2011-2012William D’haeseleer
48
Viewpoint French Academy of Sciences and Academy of Medicine…
Nuclear Energy 2011-2012William D’haeseleer
49
American Scientists defending BEIR VII, US academy of Sciences…
Stochastic Somatic effects
Nuclear Energy 2011-2012William D’haeseleer
50
A D Wrixon, “New ICRP recommendations”, Journal of Radiological Protection 28, 2008, 161–168 doi:10.1088/0952-4746/28/2/R02Available at: http://iopscience.iop.org/0952-4746/28/2/R02/pdf/0952-4746_28_2_R02.pdf
Formal ICRP Recommendation 2007Formal ICRP Recommendation 2007
Hence ~ 5 % / Sv or 50 ppm / mSv
Nuclear Energy 2011-2012William D’haeseleer
51
Stochastic Somatic effects
Biologic effects of radiation
1) Somatic effects (own-body related)a) Early effects due to acute high doses
= “deterministic effects”
b) Stochastic effects due to low doses
~ cancer development
2) Genetic effects (offspring-related)Stochastic in nature
53
Stochastic Genetic effects• Causes of mutations:
– Heat – Chemicals– Spontaneous mutations– Radiation
• NOT possible to distinguish between the causes!
• Effects: probability genetic disease (also LNT) - first-generation progeny (1990 numbers) ~ 0.3-0.5% / Sv or 3-5 x 10-6 / mSv - all later generations ~ 1% / Sv (1990 numbers)
54
Stochastic Genetic effects• Note:
Order of magnitude of about 1% per Sv (1990 numbers))
– In the US:
Natural radiation of individual to gonads ~ 0.85 mSv/a
About 300 million inhabitants
Hence 255,000 man Sv/a * 0.01 ≈ 2500 genetic diseases per
year
Is about 2% of all cases in the US
55
Stochastic Genetic effects• Note:
Order of magnitude of somebody’s risk to have a genetically “affected” child from exposure to 1 mrem=0.01 mSv (1990 numbers)
with ~ 3-5 x 10-6 / mSv ~ 3-5 x 10-8 / mrem before conception
= equivalent with waiting with conception by ~ 3 hrs
cafeine & alcohol: 1 cup of coffee ~ equivalent with 0.02 mSv
!
Stochastic Genetic effects
• But recent research has shown that earlier estimates (~1990) have been overestimated
“Radiation-induced hereditary effects have been clearly demonstrable in animal experiments involving mice and fruit flies, but never in any human populations, including the Japanese bomb survivors, medical populations, and populations affected by the Chernobyl disaster. As with cancer, there is a spontaneous rate of mutations that is ongoing in the human population, with no excess exposure to chemicals, radiation, or other mutagenic agents. About 1 in 200 pregnancies involve a baby with a chromosomal abnormality, and about 3-4% of all pregnancies result in some abnormality being expressed in the child. Increases above this baseline, for radiation-induced genetic effects, are expressed in a unique term called the Doubling Dose. This Doubling Dose is the radiation dose to the gonads that will eventually lead to a doubling of the expression of hereditary effects, over the “spontaneous” rate in the given population.” [...]
Ref: Michael G. Stabin, “Radiation Protection and Dosimetry – An Introductuin to Health Physics”, Springer, Berlin, 2008, p 98
56
Stochastic Genetic effects
[...] “In the most recent recommendations of the ICRP, however, the risk weighting factor has been decreased substantially [compared to earlier estimates], perhaps reflecting the fact that more time has gone by and no significant effects have been demonstrated in human populations.”
Ref: Michael G. Stabin, “Radiation Protection and Dosimetry – An Introductuin to Health Physics”, Springer, Berlin, 2008, p 98
57
Stochastic Genetic effects
58
A D Wrixon, “New ICRP recommendations”, Journal of Radiological Protection 28, 2008, 161–168 doi:10.1088/0952-4746/28/2/R02Available at: http://iopscience.iop.org/0952-4746/28/2/R02/pdf/0952-4746_28_2_R02.pdf
Formal ICRP Recommendation 2007Formal ICRP Recommendation 2007
Hence ~ 0.1 – 0.2 % / Sv or 1 - 2 ppm / mSv
59
Stochastic effects
60
Stochastic effects
Note: 1 rem = 0.01 Sv = 10 mSv
< 50 – 100 mSv
61
Stochastic effects
Note: 1 rem = 0.01 Sv = 10 mSv
62
Stochastic effects
Note: 1 rem = 0.01 Sv = 10 mSv
63
Stochastic effects
Note: 1 rem = 0.01 Sv = 10 mSv
Background radiation
Background radiation• Due to natural, medical & industrial
exposure• In Belgium, total annual equivalent dose:
3.6 à 5 mSv3.6 à 5 mSv• Until ~ 2000, used value was 3.6 mSv/a
– Natural: 2.6 mSv/a• Body + Cosmic + Soil/Buildings = 1.0 mSv/a• Radon = 1.6 mSv/a (average for B)
– Man made: 1.0 mSv/a• Medical = 0.95 mSv/a• Industrial (all) = 0.05 mSv/a
Background radiation• In Belgium, total annual equivalent dose:
3.6 à 5 mSv3.6 à 5 mSv
• Currently, value is 5 mSv/a !!– Natural: 2.6 mSv/a
• Body + Cosmic + Soil/Buildings = 1.0 mSv/a• Radon = 1.6 mSv/a (average for B)
– Man made: 2.4 mSv/a• Medical = 2.35 mSv/a• Industrial (all) = 0.05 mSv/a
Overconsumption with CT scans etc…
only for diagnostics; no therapy
Ref. H. Vanmarcke (SCK)
Background radiation• In Belgium, total annual equivalent dose:
3.6 à 5 mSv3.6 à 5 mSv
• Radon = 1.6 mSv/a (average for B)– But for Vl ~ 0.5 – 1 mSv/a– And for Wall ~ 2 – 4 mSv/a– Difference of Vl & Wall ~ same order as
average natural background!
Background radiation
Radon:
Daughter product of Ra-226
Background radiation• In Belgium, total annual equivalent dose:
3.6 à 55 mSv mSv
• According to LNT estimate:• ~ 5 x 10-5 per mSv• 107 Belgians ~ 2500 fatal cancers per year• Due to natural & medical causes!
7171
Background radiation
• In a lifetime (take 60 years):5 mSv/a x 60 = 300 mSv
• 300 mSv at 5%/Sv LNTH 0.015
7272
Current safety standards
• General population:
Max extra artificial dose eq (excl med)
= 1 mSv/a1 mSv/a
• Employees in nuclear sector (Belgian law)
Max extra artificial dose eq (excl med)
= 20 mSv/a20 mSv/aIn normal / routine circumstances
EU directive specifies 100 mSv/5a
7373
Current safety standards
• Employees in nuclear sector Max intervention dose recommended
= 250 mSv/a250 mSv/a
Max dose for “life saving” intervention= 500 mSv/a500 mSv/a
In exceptional / accidental circumstances (in Belgium)
Nuclear Energy 2011-2012William D’haeseleer
7474
Permissible Doses for Astronouts
References
• Some basic examples (a.o.)