Review: Is our current approach adequate

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Review Is our current approach adequate?

• Melvyn Myers
• Radiological Sciences Unit
• Hammersmith Hospital

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Radiation Protection supported by its basic
hypotheses
The World of Radiation Protection
The Linear No-threshold Theory etc.
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There is also a secondary question on the
usefulness of the idea of Collective Dose.
The adequacy of our approach comes down to the
main question
Is the LNT theory adequate (sustainable,
justifiable)?
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Basis for calculating cancer risk using LNT
single particle of radiation
single DNA molecule
cancer initiation
Cancer risk is therefore linearly dependent on
dose with no mention of a threshold
Thus the cancer risk from 0.001 Sv is 0.001 the
risk from 1 Sv
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Until the weight of the scientific evidence
indicates otherwise it would be prudent to stick
with the LNT theory
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The LNT does not apply at low doses - in fact
very low dose radiation may be good for you
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Why is it important to question the LNT Dogma?
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Supporting the principle that any radiation might
be harmful is the safest thing to do but what are
we trading off in exchange for this safety?

• Is there a circular argument here?
• We make low level doses appear
• dangerous to protect ourselves
• from low level radiation.

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Some grounds for abandoning the LNT at low doses
are
1. Ethical
2. Practical
3. Economic
4. Scientific
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Ethical Examples

• We have to avoid the fear (and its
• consequences) of low level radiation
• e.g. the thousands of reported abortions
• after the Chernobyl accident

• We have to avoid the regimented
• refusal / denial / delay of clinical
• procedures involving radiation

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Practical Examples

• The manoeuvres in hospital radiation
• protection, to reduce dose to below
• single mSv figures

• Protection of sewage plant workers

• Protection of airline staff

• How do we deal with NORM?

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Economic Examples
Billions are spent

• In cleaning up radioactive sites or
• relocating low levels of radiation

• In disposing of radioactive waste

• In reducing the levels of radon in houses

• In the cost of prevention

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Scientific Example 1.

• How do you advise a researcher whose
• request to give normal subjects a dose of
• 4 mSv to study Parkinson's disease has
• been refused and who says

But if they had moved to Cornwall they would
have received that extra radiation every year
from background?
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Scientific Examples 2.

• We are dealing with a principle of
• scientific integrity.

• We have to have a scientific reason,
• not follow a political or economic or
• irrational policy.

Is the evidence there?
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There are large numbers of papers, articles,
reviews on the validity or otherwise of the LNT
We should examine them critically but with an
open mind

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Effects of Low Doses and Low Dose Rates of
External Ionising Radiation Cancer Mortality
among Nuclear Industry Workers in Three
CountriesA study of 95,673 workers in US, UK
and Canada There was no evidence of an
association between radiation dose and mortality
from all causes and from all cancers
Mortality from leukaemia, excluding chronic
lymphocytic leukaemia the cause of death most
strongly related to radiation dose was
significantly associated with cumulative external
radiation dose
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gt
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What other evidence of similar responses are
there in the literature?

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(No Transcript)
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Excess deaths from leukaemia per 100 "expected"
among Japanese A-bomb survivors (195090) vs.
dose
Pierce D.A. et al, Studies of the mortality of
atomic bomb survivors, Report 12, Part 1, Cancer
195090, Radiation Research, vol. 146, p127,
1996.
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Relative risk of mortality from lung cancer vs.
dose to lung.
The left figure with expanded vertical scale
illustrates a study of cancer mortality in a
radiation-exposed cohort of TB patients. The
right figure shows data on lung cancer among
Canadian fluoroscopy patients. The dashed line
connects data from A bomb survivors
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The significantly different A-bomb survivor data
(much higher risk at all doses) can be explained
by the difference between very high dose rate in
the A-bomb survivors and the lower dose rate
from fluoroscopic exams extending over many
weeks.
It must give pause for thought before using
A-bomb survivor data to predict risks from LLR,
which is the method normally used.
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Collective Dose (Equivalent)
Definition
Average dose equivalent multiplied by the
number of people exposed
Units
man sievert
If one million people receive 10 mSv each the
collective dose equivalent is 10,000 man Sv

• The idea is often seen in the form of
• dividing the total dose by the number
• of people to give the average dose received
• by each - as when 10,000 Sv is spread over
• 1 million people to give 10mSv each

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(If) everyone on earth adds a 1-inch liftto
their shoes for just 1 year theresultant very
small increase in cosmicray dose would yield a
collective doselarge enough to kill 1500 people
withcancer over the next 50 years

• Marvin Goldman Cancer Risk of Low-Level
  Exposure Science 1996 272 1821-1822

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The LNT hypothesis suggests the use of
collective doses which consist of very small
doses added together.The authors conclude that
for moral, practical and legal reasons,
particularly the emphasis on individual doses to
the exclusion of societal risks and uncertainty
over effects into the distant future, collective
dose is a valid parameter which should continue
to be used for ALARA.
In defence of collective dose
Ian Fairlie and David Sumner J-Radiol-Prot. 2000
Mar 20(1) 9-19
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What are the scientific tasks ahead? 1.

• Is the LNT theory to be used at
• low dose?

• If there is a threshold, what is it ?

• What are the implications of any
• threshold (national, European,
• International)

• What is a safe level of radiation

• Does hormesis exist?

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What are the scientific tasks ahead? 2.

• How do we organise the research on this
• It needs large political will and support
• (lottery money?)

• Government initiative
• The American Department of Energy
• Low Dose Radiation Research Program

• International mixed meetings
• Radiation Policy and Science. An
• International Conference in Warrenton,
• Virginia, December 1999

• What do we do about collective dose?

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ALARA or ALARPATLAS At These Levels Act
Scientifically