Estimations of radiation-induced risks from low doses Sören Mattsson

Estimations of radiation-induced risks from low doses
and how to communicate these risks
Sören Mattsson
Medical Radiation Physics, Lund University and
Skåne University Hospital Malmö, Sweden
Medical Physics in the Baltic States
11th Conference & Workshop
10-12 October 2013
Malmö
Illustration of the dose–response relationship for radiationinduced carcinogenesis in humans. (Hall, 2004, 2009)
but …
Extrapolation models for estimating radiation risk at low dose.
Image shows 4 models: linear, no threshold (solid black
line); linear, with threshold (dashed black line); super linear (blue
line); and hormetic (red line)
(NCRP, 2008)
Hall, 2009
How the concern regarding exposure to ionising radiation
has changed from heritable effects to carcinogenesis
Radiation-induced cancer:
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Scientific basis for current radiation
protection.
Epidemiology
Survivors of Hiroshima and Nagasaki
Patients in health care (radiation
therapy, repeated diagnostic radiology,
CT investigations of children)
Occupationally exposed persons
Environmental exposures
Animal experiments
Cell research
Epidemiology:
All cancers – All ages
Deviation of cancer mortality from the average (0/00)
in 1996-2005 (SEER-USA) and radiation effects (ICRP)
Hiroshima/Nagasaki 1945
86 572 persons
Solid cancers
Solid cancers
Solid cancers
Leukaemia
Non-cancer
(cariovascular disease, cognital effects, diabetes)
Patients in healthcare
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External radiotherapy
Haemangioma treatment with 226Ra
Chest radiograph at TBC - dose to the breast
Thyroid diagnostics with 131I
In utero diagnostic x-rays
Children who were examined with CT
Occupationally exposed persons
Medical staff
Chernobyl emergency and recovery workers
Participants in nuclear weapons tests
Workers in the nuclear weapons and power
industries
• Underground miners
• Radium dial painters
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Environmental exposures
• Radon in homes
• Chernobyl contaminated areas
• Mayak, Techa river, Kyshtym
Cancer risk
• UNSCEAR, lethal solid cancer: 11% Sv –1
(men 9%, women 13%)
• Reduce with a factor of 2 at low doses or
dose-rates, which means a risk of about
5% Sv–1 (uncertainty interval: 1%-9%)
• Risk for fatal leukemia: 1% at 1 Sv;
0,05% at 0,1 Sv
Risk of dying from radiation-induced cancer later in life
(population average) according to ICRP
10% per Sv
?
5% per Sv
(1-9%)
Equivalent dose, Sv
Effective dose, Sv
Base for information about radiation risks of lowdose radiation exposure
- Health effects of low dose radiation exposure (5, 10,
20 mSv)?
- Results from epidemiology in general
- Results from epidemiology related to specific
age groups
- Biophysical arguments
- The linear non-threshold (LNT) - model
What happens at lower doses
of radiation?
Pelvimetry or obstetric
abdominal examination
There are data to support the hypothesis
that there is a risk also at lower doses
- Increased risk of cancer during childhood after X-ray in utero with 6-10 mSv
(mean 1 electron / cell)
- Biophysical argument
If the dose is reduced, we get fewer
electron tracks and fewer hits of cells.
The cells that are hit suffer the same
type of injury and the same biological
process is initiated.
- Increased risk of cancer after CTinvestigations during childhood.
Average absorbed dose: 6 mSv
80 kV x-rays
Equivalent to about 1 electron
per nucleus
Alice Stewart
(1906-2002)
The base of the biophysical argument for a
linear relationship between dose and effect
at low doses:
Track structure at 1000, 10 and 1 mSv
Risk varies with age
Risk of dying from cancer in the
rest of life (LNT-model)
Mean for population
5% per 1 000 mSv
0,5% per 100 mSv
0,05% per 10 mSv
0,005% per 1 mSv
Foetus, newborn
15% per 1 000 mSv
1.5% per 100 mSv
0.15% per 10 mSv
0.015% per 1 mSv
Compare with the "natural" risk
of dying from cancer: about 22%
Remaining questions
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Cancer
The effect of low doses and dose-rates
The effect of different types of radiation
Extrapolations over time and between countries
The importance of factors that may modify the risk
Age
Sex
Genetically determined differences in radiosensitivity
Environmental factors
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Non-cancer effects
Cardiovascular effects at low doses and dose rates
Cognitive effects
Diabetes
Communication about radiation risks
The respect and fear of radioactivity and radiation is very
deep.
In other contects the risks have been/still are neglected.
Communication of radiological risks is not an easy task.
Different in medicine and health-care than in the society
after an accident .
Some leading principles for all information
1. Transparency, openness. Tell the truth
2. Ask whether you are being understood
3. The listener must thrust on you
4. Initiative and speed
5. Quality
Transparency, openness. Tell the truth.
“Never underestimate people's talents,
but do not overestimate their knowledge”.
Take each question seriously-It is a chance to teach.
Communicate therefore, openly and clearly.
The listener must
thrust you
Requires transparency.
Avoid ”double messages”.
No danger
Dagens Nyheter 2/5 1986
It is also important how to convey the information
Example: Activity levels in food.
It is perceived very differently if you say that the limit
for Cs-137 in foodstuff is 300 Bq/kg or you say that you
have to eat 75 000 Bq to get a dose of 1 mSv. As it was
perceived, 300 Bq/kg was by many considered as a toxic
limit.
Concentration (Bq/kg)- and doserate (mSv/hr) values
that are supposed to be tolerated for a long time will
be perceived as absolute limits.
Base for information about radiation risks of
low-dose radiation exposure
- Quantities and units: Use only Bq and mSv for activity
and ”dose” respectively
http://www.imagewisely.org/Imaging-Professionals/Medical-Physicists/Articles/Howto-Understand-and-Communicate-Radiation-Risk
Comparison of dose contributions with the natural effective
dose
What to tell the radiologist and the general practitioner
Any added risk, however small, is not acceptable if it does not
benefit the patient.
Justification and optimization of a procedure are absolutely
essential.
Diagnostic reference levels should be used to reduce
variations from one center to another and to promote
optimal dose indicator ranges for medical imaging protocols.
The basic principles of radiation protection need to be
respected to help counteract the unjustified explosion in the
number of procedures now being performed.
… thank you for listening
soren.mattsson@med.lu.se
Telephone +46 40 331374
Verdun et al., 2008
Example of a risk comparison
Of 2 500 10 year old
children, 550 will die from
cancer for reasons other
than man-made sources of
ionizing radiation
A 10 year old who gets 4 mSv effective dose (Ex: CT abdomen,
bone scan). Risk of dying from radiation-induced cancer in the rest
of life: 10% per Sv. 0.004 Sv x 10% per Sv gives a risk of 0.0004 or
1 per 2 500 (the star in the picture).