Doctor Fairlie says nay one can use any part of this in response to NRC's push to make "radiation safe and beneficial for you", as long as you give him a citation.
Sorry for the horrible formatting, it was copied from a PDF.
http://www.ianfairlie.org/wp-content/uploads/2015/08/US-NRC-Consultation-4-1.pdf
1
Dr Ian Fairlie
Consultant on
Radioactivity in the Environment
LONDON
United Kingdom
www.ianfairlie.org
US Nuclear Regulatory
Commission (NRC): Consultation
https://www.federalregister.gov/articles/2015/06/23/2015-15441/linear-no-threshold-model-and-standards-for-protection-against-radiation
Introduction
On June 26 2015, the US Nuclear
Regulatory Commission (NRC) stated it was seeking public comments by September
8, on petitions stating that the Linear No Threshold theory of radiation’s
effects was not a valid basis for setting radiation standards and that the
hormesis model should be used instead.
In more detail, the NRC has
received three petitions for rulemaking requesting that the NRC amend its
“Standards for Protection Against Radiation” regulations and change the basis
of those regulations from the Linear No-Threshold (LNT) model of radiation
protection to the hormesis model. (See the Appendix for details of the
petitions.)
The LNT model assumes that
biological damage from radiation is linearly related to exposure and is always
harmful, ie without a threshold. The hormesis model assumes that exposures to
low radiation levels is beneficial and protects the human body against
deleterious effects of high levels of radiation.
The NRC has stated it is
examining these petitions to determine whether they should be considered in
rulemaking and is requesting public comments. US environmental groups are
concerned that, if the NRC agreed with the petitions, it would introduce rules
to weaken radiation protection standards at US nuclear facilities. On the other
hand, according to two NRC staffers (Brock and Sherbini, 2012), the NRC
apparently pays attention to the evidence on risks of low levels of radiation.
See references at end.
Comments on Hormesis
It is true that some cell and
animal experiments indicate that if small amounts of radiation were
administered before later larger amounts, the damage done is less than if no
previous small amount were given. (The word “tickle” is used in radiobiology
lingo to denote such small amounts.) On the other hand, other cell and animal
studies using different doses, durations and endpoints fail to show this
effect, and there is no human evidence, ie from epidemiology. But it is true
that some evidence from chemistry indicates the same effect, and there is some
theoretical support for an adaptive effect in animals and plants. 2
Hormesis advocates typically argue that although radiation
attacks DNA and causes mutations, DNA repair mechanisms quickly correct these.
These mechanisms are certainly numerous and busy – it is estimated over 15,000
repairs per hour are carried out in each cell – but from the sheer number of
repairs, many misrepairs occur and it is the misrepairs that cause the damage.
But even if
the existence of hormesis were accepted, the question remains – what relevance
would it have for radiation protection? The answer- as stated repeatedly in
official reports by UNSCEAR and BEIR etc - is zero. For example, do we give
“tickle” doses to people about to undergo radiation therapy, or to nuclear
workers? Of course, we don’t.
And what about
background radiation? All of us receive small “tickle” doses of radiation – about
3 mSv per year of which about 1 mSv is from external gamma radiation. Do these
somehow protect us from subsequent radiation? How would we notice? And if it
did, so what? That is, what relevance would it have for radiation protection,
eg setting radiation standards? The answer is again ….none. Indeed, as we show
below, increasing evidence exists that even background radiation itself is
harmful.
Comments on
LNT
On the other
hand, the scientific evidence for the LNT is plentiful, powerful and
persuasive. It comes from epidemiological studies, radiobiological evidence,
and official reports. Let’s examine these in turn.
A.
Epidemiological Studies
Does the
available epidemiological evidence show risks declining linearly with dose at
low doses? Yes, recent epidemiology studies do indeed show this, and the
important new points are that these are (a) very large studies with good
confidence intervals, and (b) at very low doses, even down to background
levels. In other words, the usual caveats about the validity of the linear
shape of the dose response relationship down to low doses are unjustified.
The most
recent evidence is from a particularly powerful study by Leuraud et al (2015)
which shows linearly-related risks down to very low levels (average dose rate =
1.1 mGy per year). http://www.thelancet.com/journals/lanhae/article/PIIS2352-3026%2815%2900094-0/fulltext
The main findings from the Leuraud study
are shown in graph 1. 3
Graph 1
Two
interesting things about this study are that 5 of the 13 authors are from US
scientific institutes, including the Centers for Disease Control and
Prevention, the National Institute for Occupational Safety and Health, the
Department of Health and Human Services, University of North Carolina, and
Drexel University School of Public Health. Also that the study was funded by
many international agencies, including the US Centers for Disease Control and
Prevention, US National Institute for Occupational Safety and Health, US
Department of Energy, and the US Department of Health and Human Service.
It is
legitimate to ask whether the NRC is in contact with these official US agencies
about its consultation.
The Leuraud et
al study is merely the latest of many studies providing good evidence for the
LNT model. Second is the Zablotska study after Chernobyl. Graph 2 below,
reproduced from Zablotska et al (2012), shows statistically significant risks
for all leukemias and for chronic lymphocytic leukemia (CLL) in over 110,000
Chernobyl cleanup workers. It can also be seen that there are 6 data points
showing increased risks below 100 mSv - a commonly cited cut-off point. 4
Graph 2
Third is the
very recent cohort study of radiation exposures from medical CT scans in the UK
by Pearce et al (2012). 74 out of 178,604 patients diagnosed with leukaemia and
135 out of 176,587 patients diagnosed with brain tumours were analyzed. As
shown in graph 3 reproduced from their study, the authors noted a positive
association between radiation doses from CT scans and leukaemia and brain
tumours .The large dashed line showed a linear fit to the data with a 95%
confidence interval shown by small dashed lines.
Graph 3 5
Fourth are the risks from background radiation – yes, even
from background radiation. Kendall et al in 2012 conducted a large UK
record-based case–control study testing associations between childhood cancer
and natural background radiation with over 27,000 cases and 37,000 controls.
Surprisingly, they observed an elevated risk of childhood leukaemia with
cumulative red bone marrow dose from natural background gamma radiation. See
the similar findings in a very recent study by Spycher et al (2015) discussed
on page 10 below.
In graph 4
below reproduced from the Kendall et al study, the x-axis represents cumulative
gamma ray doses in mGy. The red line shows not merely a linear but a slightly
supralinear curve fitted to the data. The small dotted lines mark a 95%
confidence interval.
Graph 4
Fifth is the final
analysis of the UK National Registry for Radiation Workers (NRRW). This study
of observed 11,000 cancer cases and 8,000 cancer deaths in 175,000 UK radiation
workers with an average individual cumulative dose of 25 mSv and an average
follow-up of 22 years. Graph 5 reproduced from the study shows the relative
risks for all solid cancers with the continuous blue line representing the NRRW
data, and the continuous red line the results from the US BEIR VII report for
comparison – the two are very similar, as can be seen. An estimated ERR of 0.27
per Sv can be derived from this graph. 6
Graph 5
Sixth is the
meta-analysis of 13 European studies in 9 EU countries on indoor radon exposure
risks by Darby et al (2005). This examined lung cancer risks at measured
residential Rn concentrations with over 7,000 cases of lung cancer and 14,000
controls. The action level for indoor radon in most EU countries is 200 Bq per
m3, corresponding to about 10 mSv per
year. (This is derived from a UNSCEAR (2000) reference value of 9 nSv per
Bq·h/m3. This means that people living
2/3rds of their time indoors (5,780 h/year) at a Rn concentration of 200 Bq/m3 would receive an effective dose of ~10 mSv/year. Graph 6
reproduced from the study shows elevated risks at concentrations well below
this level. The solid line is the authors’ linear fit to the data. 7
Graph 6
No evidence
below 100 mSv?
It is
necessary at this point to directly address the argument often raised by
hormesis advocates – that there is little evidence of effects below 100 mSv.
This is incorrect. Older evidence exists -see http://www.ianfairlie.org/news/a-100-msv-threshold-for-radiation-effects/
for a list of studies and the newer
evidence, as we have just seen, clearly shows this fact as well.
B. Radiobiological Evidence
Current radiobiological theory
is consistent with a linear dose-response relationship down to low doses (ie
below ~10 mSv).
The radiobiological rationale
for linearity comes from the stochastic nature of energy deposition of ionising
radiation. It was explained by 15 of the world’s most eminent radiation
biologists and epidemiologists in a famous article (Brenner et al, 2003) as
follows:
“1. Direct epidemiological
evidence demonstrates that an organ dose of 10 mGy of diagnostic x-rays is associated
with an increase in cancer risk.
2. At an organ dose of 10 mGy
of diagnostic x-rays, most irradiated cell nuclei will be traversed by one or,
at most, a few physically distant electron tracks. Being so physically distant,
it is very unlikely that these few electron tracks could produce DNA damage in
some joint, cooperative way; rather, these electron tracks will act
independently to produce stochastic damage and consequent cellular changes.
3. Decreasing the dose, say by
a factor of 10, will simply result in proportionately fewer electron tracks and
fewer hit cells. It follows that those fewer cells that are hit at the lower
dose will be subject to (i) the same types of electron damage and (ii) the same
radiobiological processes as would occur at 10 mGy. 8
4. Thus, decreasing the number of damaged cells by a factor
of 10 would be expected to decrease the biological response by the same factor
of 10; i.e., the response would decrease linearly with decreasing dose. One
could not expect qualitatively different biological processes to be active at,
say, 1 mGy that were not active at 10 mGy, or vice versa. The argument suggests
that the risk of most radiation -induced endpoints will decrease linearly,
without a threshold, from ~10 mGy down to arbitrarily low doses.”
C. Official
Reports
Both types of
evidence (epidemiology and radiobiology) have been examined in 4 international
official reviews: UNSCEAR (2008), US NCRP Report No 136 (2001), US BEIR VII
(2006) and ICRP 99 (2006). These reports confirmed the LNT as being the most
prudent assumption for radiation protection purposes.
For example in
2006, the chair of BEIR VII, Richard R. Monson, associate dean for professional
education and professor of epidemiology, Harvard School of Public Health,
Boston stated "The scientific research base shows that there is no
threshold of exposure below which low levels of ionizing radiation can be
demonstrated to be harmless or beneficial". http://hps.org/documents/BEIRVIIPressRelease.pdf
Recently, the US-based scientist
Mark Little and his colleagues (Little et al, 2009) examined the matter in
considerable detail. They discussed (i) the degree of curvature in the cancer
dose response within the Japanese atomic bomb survivors and other groups, (ii)
the consistency of risks between the Japanese and other low-dose cohorts, and
(iii) biological data on mechanisms. They concluded linearity was the best bet.
Also in 2009, the head of the
US Environmental Protection Agency’s radiation section reviewed the matter in
an influential article (Puskin, 2009). He stated “Although recent
radiobiological findings indicate novel damage and repair processes at low
doses, LNT is supported by data from both epidemiology and radiobiology. Given
the current state of the science, the consensus positions of key scientific and
governmental bodies, as well as the conservatism and calculational convenience
of the LNT assumption, it is unlikely that EPA will modify this approach in the
near future”.
The Importance of LNT in
Radiation Protection
Regardless of dissenting views
on LNT, the reality is that most concepts used in radiation protection today
are fundamentally based on the LNT theory. For example, LNT underpins the
concepts of absorbed dose, effective dose, committed dose, and the use of dose
coefficients (ie Sv per Bq of a radionuclide). It also allows radiation doses
(i) to be averaged within an organ or tissue, (ii) to be added from different
organs, and (iii) to be added over time.
LNT also permits annual dose
limits; optimization -ie comparison of practices; radiation risk assessment at
low and very low doses; individual dosimetry with passive detectors; collective
dose, and dose registers over long periods of time. 9
In fact, the LNT underpins all legal regulations in radiation
protection in the US and in the rest of the world. Indeed, if the LNT were not
used, it’s hard to imagine our current radiation protection systems existing at
all. However this statement should not be misconstrued to mean that the LNT is
used just because it’s convenient: the LNT is used because the scientific
evidence for it is comprehensive, cogent and compelling.
Statistical
Significance
It is
necessary to discuss the vexed issue of statistical significance, as hormesis
advocates (eg http://atomicinsights.com/leukemia-and-lymphoma-study-recently-published-in-lancet-being-strong-challenged-by-sari/) often dismiss studies stating they show “no
significantly” raised risks at low levels, or that excess risks are “not significant”
at low levels, or similar phrases.
Let’s examine these phrases
because they can mislead readers into incorrectly thinking that the reported
increase is “unimportant” or “irrelevant”. The word “significant” is a
specialist adjective used in statistical tests to convey the narrow meaning
that the likelihood of an observation being a fluke is less than 5% (assuming a
p = 5% test was used). It does not mean important or relevant.
Secondly, such phrases are
often glibly used by hormesis advocates without explaining that the test level
used is quite arbitrary. There is no scientific justification for using a 5% or
any other test level: it is merely a matter of convenience. In other words, it
is quite possible for results which are “not significant” when a 5% test is
applied, will become “significant” when a 10% test is used. For this reason,
good epidemiologists nowadays have stopped using the words “significant” or
“significance” altogether. Instead they use confidence intervals: hormesis
advocates should follow suit.
There is a third reason why
these phrases shouldn’t be used. Scientifically speaking, it’s bad practice to
dismiss results (or to imply this) just because they do not meet a statistical
test. This is because the probability (ie p value) that an observed effect may
be a fluke is affected by both magnitude of effect and size of study (Whitely
and Ball, 2002). This means statistical tests must be cited with caution, as
the use of an arbitrary cut-off point for statistical significance (often p =
5%) can lead to incorrectly accepting the null hypothesis - ie that there’s no
effect (Sterne and Smith, 2001). This is called a type II error in statistics,
and it often occurs in studies due to low numbers1 of observed cases (Everett et
al, 1998) rather than lack of effect. In other words, the rejection of findings
for statistical reasons can often hide real risks (Axelson, 2004; Whitley and
Ball, 2002).
1 It should be borne in mind
that low case numbers are not the fault of researchers but often due to the
fact that many conditions are rare (eg child leukemia) and very large numbers
of exposed people are needed to pick up the few observed cases.
So what should hormesis
advocates do with a study having positive findings which do not meet their
self-selected 5% test? First of all, they should NOT reject the findings.
Instead they should report the observed increase and add there’s a greater than
5% possibility this could be a chance finding. And then they should discuss 10
whether their interpretation would change if a slightly less
strict 10% test were chosen (as is increasingly used nowadays). And they should
discuss the confidence interval so that readers can make up their own minds.
For example, they could say that the relative risk was, say, 1.55 with a 90%
confidence interval of 1.01 to 1.98. This would mean that the observed relative
risk was 1.55 and that we are 90% sure that the real value lies between 1.01
and 1.98. The key point is that the loaded words “significant” or
“significance” are therefore avoided.
Conclusions
(i) the
debate
The validity
or otherwise of LNT and hormesis have been the subject of hundreds of
scientific articles and debates over several decades. Unfortunately, much of
the literature on hormesis or adaptive response is based on faulty science or
on misconceptions, or on misinterpretations, or on all three. This is
particularly the case with several US and UK journalists who write with
confidence on how radiation risks are exaggerated. Their knowledge and
experience of radiogenic risks are limited to say the least, but these journalists,
almost on a weekly basis, misinform and mislead the public about radiation
risks, so the existence of the US petitions is perhaps unsurprising.
However real
scientists are increasingly standing up and opposing the poor science used by
hormesis advocates. Very recently, four Swiss scientists from the Institute of
Social and Preventive Medicine at the University of Bern; the Swiss Tropical
and Public Health Institute, Basel and the University of Basel published a
study which revealed that exposure to high rates of background radiation
resulted in increased cancer risks to children (Spycher et al, 2015). http://ehp.niehs.nih.gov/1408548/
In reply, 17 scientists (Siegel
et al, 2015) mostly from the US, some of whom were members of a hormesis
pressure group “Scientists for Accurate Radiation Information” objected to
these findings. They alleged that the government would have to evacuate
children living in higher radiation areas and relocate them to lower radiation
areas. They stated that studies like this should not be taken seriously without
public health policy implications being examined. (http://ehp.niehs.nih.gov/1510111/)
The Swiss scientists in turn
responded (http://ehp.niehs.nih.gov/1510111R/) that the proposed evacuation was “nonsensical” in
view of the very low numbers involved. In a spirited rejoinder, they refuted
the poor science cited and added that “the Scientists for Accurate Radiation
Information a priori exclude the possibility that low-dose radiation
could increase the risk of cancer. They will therefore not accept studies that
challenge their foregone conclusion”.
(ii) the petitions
After briefly examining the
three US petitions, my conclusion is that they do not merit serious
consideration. It seems that the petitioners, who may or may not have axes to
grind about radiation risks, have seized on the possible phenomenon of hormesis
11
to make ill-considered claims that radiation is protective or
even good for you. In other words, the petitions appear to be based on
preconceptions, or even ideology, rather than the scientific evidence which
points in the opposite direction.
The petitions
should not be used by the NRC to justify weakening regulatory standards at US
nuclear facilities. A question remains whether the NRC should have accepted the
petitions for review. Presumably the NRC has discretion not to review or to
refer back spurious, mischievous, or ill-founded petitions.
The NRC should
seek guidance from the five US scientific agencies and Government departments
mentioned above whose scientists have published evidence on the matter.
Credits.
Thanks to Dr Jan Beyea, Cindy Folkers, Dr Alfred Körblein, Xavier Rabilloud, Dr
Marvin Reznikoff and Dr Gordon Thompson for comments on drafts. Any errors are
my responsibility.
References
Axelson O.
Negative and non-positive epidemiological studies. Int J Occup Med Environ
Health. 2004;17:115-121.
BEIR VII
(2006) http://www.nap.edu/catalog/11340/health-risks-from-exposure-to-low-levels-of-ionizing-radiation
Brenner David J, Richard Doll, Dudley
T. Goodhead, Eric J. Hall, Charles E. Land, John B. Little, Jay H. Lubin, Dale
L. Preston, R. Julian Preston, Jerome S. Puskin, Elaine Ron, Rainer K. Sachs,
Jonathan M. Samet, Richard B. Setlow and Marco Zaider (2003) Cancer risks
attributable to low doses of ionizing radiation: Assessing what we really know.
PNAS. vol.100 no.24. pp 13761-13766. www.pnas.orgjcgijdoij10.1073jpnas.2235592100
Brock TA and Sherbini SS (2012)
Principles in practice: Radiation regulation and the NRC. Bulletin of the Atomic
Scientists 2012 68: 36. http://bos.sagepub.com/content/68/3/36
Cardis et al (2005) Risk of
cancer after low doses of ionizing radiation: retrospective cohort study in 15
countries. BMJ. 2005 Jul 9;331 (7508).
Darby et al (2005) Radon in
homes and risk of lung cancer: collaborative analysis of individual data from
13 European case-control studies. BMJ 2005;330:223.
Everett DC, Taylor S, Kafadar
K. Fundamental Concepts in Statistics: Elucidation and Illustration. J of
Applied Physiology 1998; 85(3):775-786.
Kendall G M, M P Little, R
Wakeford, K J Bunch, J C H Miles, T J Vincent, J R Meara and M F G Murphy
(2012) A record-based case–control study of natural background radiation and
the incidence of childhood leukaemia and other cancers in Great Britain during
1980–2006. Leukemia (5 June 2012) | doi:10.1038/leu.2012.151
Leuraud, Klervi et al (2015)
Ionising radiation and risk of death from leukaemia and lymphoma in
radiation-monitored workers (INWORKS): an international cohort study. The
Lancet Haematology. Published Online: 21 June 2015.
Little MP, Wakeford
R, Tawn EJ, Bouffler SD, Berrington de
Gonzalez A. Risks associated with low
doses and low dose rates of ionizing radiation: why linearity may be (almost)
the best we can do. Radiology.
2009 Apr;251(1):6-12. doi:
10.1148/radiol.2511081686. 12
Muirhead et al (2009) Mortality and cancer incidence
following occupational radiation exposure: third analysis of the National
Registry for Radiation Workers. Br J Cancer 2009; 100: 206-212.
Pearce et al
(2012) Radiation exposure from CT scans in childhood and subsequent risk of
eukaemia and brain tumours: a retrospective cohort study. The Lancet. June 7,
2012. 380: 499-505. DOI:10.1016/S0140-6736(12)60815-0, http://press.thelancet.com/ctscanrad.pdf
Puskin J (2009) Dose-Response
Vol 7:284–291. Perspective On The Use Of LNT For Radiation Protection And Risk
Assessment by the U.S. Environmental Protection Agency.
Siegel JA et al (2015) Comment on “Background Ionizing Radiation and the Risk
of Childhood Cancer: A Census-Based Nationwide Cohort Study” Environ Health
Perspect; DOI:10.1289/ehp.1510111
Spycher BD, Martin Röösli,
Matthias Egger and Claudia E. Kuehni (2015) Response to “Comment on ‘Background
Ionizing Radiation and the Risk of Childhood Cancer: A Census-Based Nationwide
Cohort Study’. Environ Health Perspect; DOI:10.1289/ehp.1510111R
Sterne JAC, Smith GD. Sifting
the evidence--what's wrong with significance tests? Phys Ther (2001)
81(8):1464-1469.
United Nations Scientific
Committee on the Effects of Atomic Radiation (2008). UNSCEAR Report to the
General Assembly, with scientific annexes – Annex B, § 153.
Whitley E, Ball J. Statistics
Review 1: Presenting and summarising data. Crit. Care 2002; 6:66-71.
Zablotska et al (2012)
Radiation and the Risk of Chronic Lymphocytic and Other Leukemias among
Chornobyl Cleanup Workers. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.1204996 Online 8 November 2012.
Appendix: Views of US
Petitioners
On February 9, 2015, Dr. Carol
S. Marcus, a Professor of Radiation Oncology, of Molecular and Medical
Pharmacology (Nuclear Medicine), and of Radiological Sciences at the David
Geffen School of Medicine at the University of California-Los Angeles, filed a
petition for rulemaking with the Commission, PRM-20-28 (ADAMS Accession No.
ML15051A503). Dr. Marcus was a member of the NRC's Advisory Committee on the
Medical Uses of Isotopes from 1990 to 1994. The petitioner indicated that
“[t]here has never been scientifically valid support for this LNT hypothesis
since its use was recommended by the U.S. National Academy of Sciences
Committee on Biological Effects of Atomic Radiation (BEAR I)/Genetics Panel in
1956” and that “[t]he costs of complying with these LNT based regulations are
enormous.”
On February 13, 2015, Mr. Mark
L. Miller, a Certified Health Physicist, filed a petition for rulemaking with
the Commission, PRM-20-29 (ADAMS Accession No. ML15057A349). The petitioner
indicated that “[t]here has never been scientifically valid support for this LNT
hypothesis” and that “[t]he costs of complying with these LNT-based regulations
are incalculable.” In addition, the petitioner suggests that the use of the LNT
hypothesis has “led to persistent radiophobia [radiation-phobia].”
On February
24, 2015, Dr. Mohan Doss, filed a petition for rulemaking with the Commission,
PRM-20-30 (ADAMS Accession No. ML15075A200). Dr. Doss filed this petition on
behalf of Scientist for Accurate Radiation Information, whose mission is to
“help prevent unnecessary, radiation-phobia-related deaths, morbidity, and
injuries associated with distrust of radio-medical diagnostics/therapies and
from nuclear/radiological emergencies through countering phobia-promoting
misinformation spread by alarmists via the news and other media including
journal publications.”
No comments:
Post a Comment
Insightful and Relevant if Irreverent Comments