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McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Health Physics563-613B
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Risk and Dose Limits
Michael EvansLecture 3 (Sep. 24, 2004)
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
RISK
Hazard: anything that can cause harm ( e.g., chemicals, electricity, working from ladders, etc..
Risk: is the chance, high or low, that somebody will be harmed by the hazard
American Cancer Society
www.cancer.org
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Cause-consequenceAnalysis
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Cause-consequence analysis revolves around decision trees and the assumption that truly independent variables contribute to occurrences and outcomes. That is, what independent things must conspire together to bring about an event, and having occurred, what are the
possible outcomes.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
RISKFault Tree
A "fault" tree is effectively a statement of what events have to conspire together to bring about an undesired outcome. Traditionally these have been drawn top-down and therefore the undesired event known as the "top event". Because of the logical hierarchy of the items, it can be sometimes seen as a form of time sequence going from the bottom towards the top of the page.
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McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
RISK : Differing Perceptions
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McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Nuclear Industry Advertisement @ 1970s
Many different types of radiation may have different effects on cancer rates.Experiments with humans cannot be set up so effects are not well known.Different age and sex groups vary in sensitivity.A single big dose has a greater net effect over time than the same dose spread out over small increments.Extrapolation from high doses: we don't know how to extrapolate to low doses.
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McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
RISK: Perception
Risk is the probability of consequence.The perception of risk is determined by how the individual views its probability and its severity
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
RISK: Perceptionand Decision Tables
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
RISK PERCEPTION
Smoking ( 45,000 deaths per year - Canada)
Smoke Alarms (368,000 home fires US, 16,975 injuries and $5.5 billion in property damage)
Fire Extinguishers (85% of fire-related deaths occur in home fires)
Radon (from 7,000 to 30,000 deaths per year -USEPA)
Driving (Nearly 3,000 people died and 217,614 were injured Canada)
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McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
RISK
1. Understanding Risk (Fischoff et al.)
2. Assessing risk involves decisions.
3. No approach is comprehensive - there are always biases.
4. Personal beliefs affect our interpretation of fact.
5. determining factors in risk decisions relate to the definition of the problem ( consequences, uncertainties…).
6. Decisions may be influenced through subtleties in the wording of the problem or the question.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Data Interpretation:Radon
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Radon- Canadian recommendations
Although provincial and territorial governments have jurisdiction over the health effects of background radiation, Health Canada has recommended that the guideline for exposure to radon gas should be 800 becquerels per cubic metre as the annual average concentration in a normal living area. The guideline is an upper limit, and Health Canada recommends taking action to reduce radon levels in your home if they exceed the limit. Because there is some risk at any level of radon exposure, homeowners may want to reduce their exposure to radon, regardless of levels.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Radon- US EPA recommendations
Radon is a radioactive gas and has been identified as a leading cause of lung cancer, second only to cigarette smoking in the United States. EPA's most recent health risk assessment estimates that 21,000 lung cancer deaths each year are due to radon.Test your home for radon, and have it fixed if it is at or above EPA's Action Level of 4 picocuries per liter. You may want to take action if the levels are in the range of 2-4 picocuries per liter. Generally, levels can be brought below 2 pCi/l fairly simply.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Health Effects : Radiation
Possible health effects from exposure to radiation may include cancer, birth defects in future generations and cataracts. These effects have been observed in studies of medical radiologists, uranium miners, radium dial painters, radiotherapy patients and atomic bomb survivors
Observations are based on doses that are much higher than workers who are occupationally exposed. The Linear-non-threshold theory has not been reasonably proven down to low doses, and there have been no strong cause-effect studies showing relationships between low doses and health effects.
Still prudent to assume that there are some health effects at lower doses
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Health Effects : Radiation
Genetic damage may be caused by low doses although no direct evidence of this exists.
Acute radiation exposure may cause both prompt and delayed effects.
Chronic exposure ( small doses delivered over long time periods) may cause delayed effects but not prompt effects.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Health Effects : Radiation
Prompt effects: observable after large doses in a short period of time. 450 cSv in one hour will cause vomiting and diarrhea in a few hours; loss of hair fever and weight loss within a few weeks: 50 % chance of death within 60 days without medical treatment (LD 50-60).
Delayed effects such as cancer may occur years after exposure to radiation.
Genetic effects can occur when there is damage to the genetic material. Effects may show up in future generations although to date there have been no clear observations indicating genetic effects caused by radiation in human populations.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Cancer Induction
-Radiation can damage cell chromosomes causing the cell to undergo uncontrolled growth (malignancy).
- Radiation may suppress the bodies’ natural immune system causing a reduce resistance to existing viruses which can multiply and damage cells
- Radiation may activate viruses dormant in the body which then attack cell control mechanisms causing rapid growth
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Effects
Deterministic effects : describe organ killing or dysfunction that is thought to have a certain threshold dose above which the effect is almost certain to appear.
Stochastic effects : describe random effects which can be predicted for,populations and not for individuals. They are usually applied to low dose & dose-rate situations.
Stochastic effects may occur in the individual and are termed somatic ( cancer induction ). Stochastic effects which are passed on to future generations in the germinal cells are hereditary or genetic.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risks of RadiationDose(mSv) vs Possible Effects
10 000 instantaneous Immediate illness and possible death if untreated.
1 000 instantaneous Illness (nausea) but death unlikely.1 000 chronic Long term cancer induction in one in
20 - 25 persons.
50 No evidence of consequences - NEW yearly limit CNSC.
10 Natural background level for some populations - India.
2.2 Average annual dose received by all Canadians. No observable effects.
1 Yearly limit to the public with respect to CNSC licensed facilities.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risks of Radiation
Dose ( mSv) Possible Effects
5000 - 8000 to gonads Permanent sterility in males and females
200 to testes Temporary reduction in sperm count
No effect on sexual function
< 50 whole body No observed effect on fertility sexual function
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Population groups
Japanese A-bomb- acute victims and survivors
Patients exposed to radiation for medical reasons - TB using lung and thymus irradiation- ankylosing spondilitis- secondary cancers from radiation therapy (Hodgkins, contralateral breast…)- Thorotrast and Radium 224 studies
Workers- uranium miners- radium dial painters- U.S. Nuclear Navy Shipyard (NNS) workers
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Population groups
Japanese A-bomb-dosimetry is unsure-single ethnic population makes worldwide extrapolation difficult-high dose & dose-rate
Patients exposed to radiation for medical reasons -data is often anecdotal-genetic effects are not reliably recorded
Workers-other factors such as cigarette smoking, toxins in
the work environment may confound results
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Population data from lab studies
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Linear No-Threshold Theory(LNT)
Extrapolation from the high dose region down to the low dose region causes problems in estimating the effects of low-level radiation
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Model Fitting
No Threshold
Classic LNT (Linear No-Threshold Theory)
Parabolic limiting
Hormesis
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McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Central Requirements for Radiation Protection
ICRP 26:
1 No practice shall be adopted unless its introduction produces a net benefit
2 All exposures shall be kept as low as reasonably achievable, economic and social factors being taken into account (ALARA)
3 The dose equivalent to individuals shall not exceed the limits recommended for the appropriate circumstances by the Commission
Benefits Detriment
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Central Requirements for Radiation Protection
ICRP 60 § 115 - 129 :
Justification (net benefit)
Optimization (ALARA)
Dose Limits
Potential exposures
Benefits Detriment
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Basic Units
Exposure» Total charge of ions of one sign produced in air» C/kg, 1 R = 1 esu/cm3 air = 2.58 x 10-4 C/kg
Absorbed dose» Energy absorbed per unit mass» 1 Gy = 1 J/kg = 100 rad
– 1 cGy ≈ 1 R (numerically)
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Equivalent dose
• Not all radiation produces the same endpoint– 1 mGy of photons or 1 mGy of neutrons
– radiation weighting factors used to modify the absorbed dose to express the same levels of risk between radiations
– units: 1 Sv = 1 J/kg = 100 rem
n
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Effective dose
Not all tissues have the same risks» 1 mSv on lungs or 1 mSv on the large intestine
» tissue weighting factors used to modify the equivalent dose to express the same levels of risk between tissues
» units: 1 Sv = 1 J/kg = 100 rem
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Estimates of Cancer Incidencefrom Low-Level Radiation
Number of additional cancers estimated to occur in 1 million people after exposure of each to 10 mSv of radiation
SourceBEIR, 1980 160 - 450
ICRP, 1977 200
UNSCEAR, 1977 150 - 350
Average for this example - 300
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Estimates of Cancer Incidencefrom Low-Level Radiation
American Cancer Society estimates that 25% of all adults in the 20 - 65 year group will develop cancer from all causes ( smoking, food, drugs, lifestyle …).
A population of 10, 000 not occupationally exposed to radiation will express 2,500 cases of cancer.
If all 10, 000 were exposed to 10 mSv we estimate 3 extra cases to develop. (Cancer rate has increased from 25% to 25.03 %).
A lifetime occupational dose of 100 mSv might increase chances to 25.3% and 1000 mSv to 28%. (This assumes a simple linear model).
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risks and Collective Dose
Collective dose is the sum of all dose received by all workers in a defined population.
If 100 workers out of a population of 200 each receive a dose of 2 mSv, the average dose per worker is 1 mSv and the collective dose is 200 person- mSv.
The total additional risk is assumed to depend upon the collective dose.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risks and Collective Dose
For radiation protection the risk is assumed to be proportional to the amount of dose - not the rate at which it is received.
For a given collective dose the risk is assumed to be the same even if a large number of people share the dose.
Therefore spreading out the dose on a large population may reduce the individual risk, but not that of the whole population.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Estimates of Collective Dose
Source Average individual dose (U.S.)
mSv / yearNatural background 1.0Releases - mining, milling etc. 0.05Medical 0.54Nuclear fallout 0.08Nuclear Energy 0.003Radon Gas & Daughters 1.98
Total 3.652
The average individual in the population receives about 3.6 mSv from natural and man-made environment.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risk and dose limits
The risk associated with 1 mSv/year is calculated to build up to 1 extra cancer death in 100,000 persons per year after sustaining many such years of exposure. (BEIR, AAPM 18)
Canada 2004
New Cases of Cancer: 458/100,000
Cancer Deaths : 215 / 100,00
Or a 1/1 million chance per 0.1 mSv/year
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Comparing Health Risks
Health Risk Days of life expectancy lost
Smoking 20/day 2,370 (6.5 years)Overweight 20% 985 (2.7 years)All accidents 435 (1.2 years)Auto accidents 200Alcohol 130Home accidents 95Drowning 41Natural background radiation 8Diagnostic X-rays 6Catastrophes (earthquakes…) 3.510 mSv occupational 1
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Cancer death probabilityICRP 60 C.2
Simple additive model.
The excess probability rate after a single dose, D, is assumed to be proportional to the dose, but first after a minimum latency period and over a ‘plateau” period of time.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Cancer death probabilityICRP 60 C.2
Simple multiplicative model.
The excess probability after a single dose, D, is also assumed to be proportional to the background rate of cancer death , B (u).
Age (u)
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Mortality AttributesICRP 60 pp153 & C.8
Choice of dose limits:
Lifetime death probability.Time lost due to deathReduction of life expectancyAnnual distribution of death probabilityIncrease in age specific mortality
C.8 Change in the total conditional death probability rate after an exposure of 50 mSv per year from age 18 to age 65 years.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
ICRP 60 (§ 89)Probability Co-efficients for stochastic effects
Exposed Population Detriment
Adult WholeWorkers Population
Fatal cancer 4%/Sv 5%/Sv
Non-fatalcancer 0.8%/Sv 1.0%/Sv
Severe hereditaryEffects 0.8%/Sv 1.3%/Sv
Total 5.6%/sv 7.3%/SvValues between populations differ due to differences in age distributions.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Historical dose limits
Maximum permissible doses have been applied to four population groups:
Occupationally exposed persons
Members of the public near radiation sources
The whole population (average dose)
The developing fetus
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Historical dose limits USA
Occupational Maximum Permissible Dose
1934 200 mrem (2 mSv) / day ICRP
1936 100 mrem (1 mSv) / day NCRP
1948 300 mrem (3 mSv) / week NCRP
1957 * 100 mrem (1 mSv) / week NCRP
* similar to current value
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
ICRP 60 (§ 194)Recommended dose limits
Application Occupational Public
Effective dose 20 mSv/y 1 mSv/yaveraged over definedperiods of 5 years(not to exceed 50 mSv inany single year).
Annual equivalent doseLens of eye 150 mSv 15 mSvSkin 500 mSv 50 mSvHands and feet 500 mSv
Effective dose (E): sum of weighted equivalent doses in all the tissues and organs of the body..Equivalent dose (H): average dose in tissue or organ multiplied by the radiation weighting factor.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
“Old” Canadian Dose Limits
Atomic Radiation Control Act Amended SOR/85–355
whole bodygonads, bone marrow
publicmSv/year
atomic radiation workermSv/quarter mSv/year
30 5
bone, skin, thyroid 150 30
extremities (hands, feet)
15lungs, eyes & single organs
10 mSv to abdomen for balance0.6 mSv per two weeks
pregnant ARW
30
50
300
380 750
80 150
*
‡
* effective dose‡ equivalent dose
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
NRC Dose Limits
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Workers Limits
Why are workers limits 20x higher?– monitored by Health Canada– most do not actually receive this limit– public includes children– occupational hazard– benefit of working– radiation workers are a small fraction of the total
population and the additional health burden on society is acceptable
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Occupational exposures
This can all seem a bit abstract but…
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Occupational exposures
Radiation is invisible to our senses of sight, feel, hear, taste, smell.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
ALARA / ALARP
As Low As Reasonably Achievable / Practicable( economic and social factors being taken into
account)
The key word is “reasonable”. In radiation safety there are three basic principles.
Distance : 1/d 2
Time : 1/t
Shielding : e -x
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
ALARA / ALARP
Different safety conditions require a judicious choice of these principles.
Brachy (sources) : Distance , Time , Shielding
Diagnostic : Distance , Shielding
Therapy : Shielding, Distance , Time
Shielding is often the intuitive choice but not always the best. It can give a false sense of security, slow down safe practices and even create
unwanted radiation in the case of - emitters.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Cost-Benefit AnalysisICRP 37 § 30
In the case of the introduction of a practice involving radiation exposures, the net benefit to society can be ideally expressed as:
B = V - (P + X + Y) where
B is the net benefit from the introduction of the practice,V is the gross benefit,P is all production costs excluding radiation protection costs (materials, salaries, infrastructure…),X is the cost of achieving a select level of radiation protection (shielding, detectors, salaries…),Y is the cost of the detriment due to the level of radiation protection (psychological and social factors …).
…UNITS?….
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Cost-Benefit AnalysisICRP 37 § 31
Optimizing
B = V - (P + X + Y)
Involves an interplay of production and detriment costs such that their sum
X()+ Y() is a minimum.The cost of protection and the cost of the detriment are functions of the level of protection (), - e.g. shielding thickness, ventilation rate, alternate options of protective equipment).Generally assumed that V and P are independent of .
§ 34 - optimization is an intuitive process
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Cost-Benefit AnalysisICRP 37 § 35
Concept of detriment developed to quantify all deleterious effects due to exposure to ionizing radiation. These effects do not include other harmful effects caused by conventional injuries (burns, crush, toxins …) that may be incurred in obtaining the selected level of radiation protection.
It is difficult to assign $ values to all variables ( V , the gross benefit and Y, the detriment include other elements such as stress).
Optimizing B = V - (P + X + Y) may vary from simple to complex.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risk & Cost-Benefit AnalysisICRP and NCRP
ICRP Publication 45: Quantitative Bases for Developing a Unified Index of Harm, 1986.
ICRP Publication 83: Risk Estimation for Multifactorial Diseases, 2000.
ICRP Publication 37: Cost Benefit Analysis in the Optimization of Radiation Protection, 1983
NCRP 139: Risk-Based Classification of Radioactive and Hazardous Chemical Wastes (2002)
NCRP 126: Uncertainties in Fatal Cancer Risk Estimates Used in Radiation Protection (1997)
NCRP 115: Risk Estimates for Radiation Protection (1993)
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Radiation Hormesis…its not the poison but the dose…
The A-bomb survivors are living longer than the controls despite the 400+ radiation induced cancer deaths. The increase in cancer deaths caused by radiation is only about 1% of all deaths among the survivors. In the U.S. the cancer death rate varies about 50% from the lowest cancer death rate - Utah - to the highest - Washington DC. A one percent increase in cancer deaths would not be detected in the US.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Radiation Hormesis…its not the poison but the dose…
There have been about 90,000 children and grandchildren of the A-bomb survivors and still no detectable increase in genetic mutations. Fruit flies and mice show genetic mutations but so far, no humans. All animals have repair mechanisms, humans seem to have better than average
At moderate doses, about 10 cSv, the A-bomb survivors had about 100 fewer cancers than the unexposed population - about 1900 cancers for the exposed group and about 2,000 for the controls. This doesn't prove radiation hormesis but it is inconsistent with the LNT model..
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Hormesis
In 1925 the radium dial industry forbade painters from touching the brush to their tongue. No person who started work after 1925 ever had radium induced bone cancer! (Do you still think the LNT model makes sense?)
Most of our internal radiation dose comes from natural potassium-40. An adult has about 4,000 Bq (decays per second) or about 20 million per hour! Billions of our cells are irradiated every hour - do you think one more gamma ray may cause cancer?
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Galactic Cosmic Radiation
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Galactic Cosmic Radiation
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Cosmic Rays
Cosmic ray exposure increases with altitude» air flights are closer to the cosmic ray source
– 5 µSv/hr for commercial air flights– airline flight crews receive 1 mSv/y
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risk reduction
Therac 25 Radiotherapy MachineThe Therac 25 was a radiation therapy system that intermittently gave the wrong radiation doses over a period of three years (1985-87) due to errors in the software controlling its operation. The major problems with the system have been attributed to poor interface design and software failure. Six accidents, three of them fatal, have been attributed to failures in Therac 25.The basic issue involved the replacement of hardware interlocks used in previous models with a software-only system.
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McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risk reduction
State
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www.smi.stanford.edu/.../ humanerrortalk.html
Electron mode involved a low-power electron beam, while photon (X-ray) mode involved a high power electron beam (3 orders of magnitude more powerful), but with a metal plate between it and the patient, to generate the X-rays. The electron beam must be in low-power mode if the plate is not present, and in earlier designs (Therac 6 and Therac 20) there was a mechanical device which physically ensured this. This hardware interlock wasremoved from the Therac 25 which was left to rely on a (faulty) software interlock.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risk reduction
The software was poorly designed and specified, and much of it was imported as-is from the previous models despitechanges in requirements. The problem was compounded by a complex user interface. In some cases, if the operatortried to enter certain control sequences (either in error or as shortcuts), the machine would operate incorrectly, usingthe high-power beam with no plate. It would then report an error, which it would normally do when no treatment hadbeen delivered, often leading operators to repeat the process.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Fetal Irradiation
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Risk of childhood cancer from fetal irradiation R Doll and R Wakeford 1997
The excess relative risk obtained from combining the results of these studies has high statistical significance and suggests that, in the past, a radiographic examination of the abdomen of a pregnant woman produced a proportional increase in risk of about 40%. The excess absolute risk coefficient at this level of exposure is approximately 6% per gray, although the exact value of this risk coefficient remains uncertain.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Radiation & Pregnancy
Effect NaturalFrequency
AdditionalCases After
10 mSvSpontaneous
Abortion3000 to 5000 none
CongenitalAnomalies
600 to 800 none
MentalRetardation
~ 80 none
ChildhoodCancer
20 5
LifetimeFatal Cancer
~ 2500 15
GeneticDefects
~ 2500 2
per10,000births orconceptions
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Fetal Irradiation
ICRP 60 pp 90
The effects of antenatal exposure depend on the time of the exposure relative to conception.When the number of cells is small the damage is most likely to be an undetectable death.Exposure in the first three weeks is unlikely to result in deterministic or stochastic effects in the live-born child.During major organogenesis (> 3 weeks) malformations may be formed. These effects are deterministic in character with a threshold in man, estimated from animal experiments, to be about 0.1 Gy ( 100 mSv).
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Fetal Irradiation
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
“10 day/28 day rule”: obsolete
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Radon in the early 20th C
“Weak Discouraged Men!Now Bubble Over with Joyous Vitality through the Use of Glands and Radium “
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are needed to see this picture. Radioactive
toothpaste
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Hormesis and radon today!Radon therapy effective for - but not limited to - the following immune system conditions and symptoms:• Ankylosing Spondylitis (AS)• Diabetes Type I & II• Migraine Headaches• Arthritis (OA, RA, JRA, etc.)• Eczema• Mobility• Asthma• Emphysema• Multiple Sclerosis (MS)• Behcet's• Fibromyalgia• Post Polio Syndrome (PPS)• Bronchitis• Gout• Prostate (BPH)• Bursitis• Hayfever• Psoriasis• Cancer (Breast)• High Blood Pressure• Scleroderma• Carpal Tunnel• Inflammation• Sinus• Chronic Pain• Lupus (SLE)• Ulcerative Colitis• Circulation
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
McGill University Health CentreCentre de Santé de l’Université McGill563-613B L#3 MDCE Sep24”04
Risky business…
..the (HPS) has concluded that estimates of risk should be limited to individuals receiving a dose of 5 rem (50 mSv) in one year or a lifetime dose of 10 rem (100 mSv) in addition to natural background. Below these doses, risk estimates should not be used: expressions of risk should only be qualitative emphasizing the inability to detect any increased health detriment (I.e., zero health effects is the most likely outcome).