IRSN summaryof the UNSCEAR
reports// for 2003–2007
Version dated 15 september 2006

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IRSN summaryof the UNSCEAR
reports// for 2003-2007

First edition 15 september 2006
IRSN report 2006-74
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IRSN
//short view
The Institute for Radiological Protection and Nuclear Safety (IRSN),
created by the law n°2002-254 of May 09, 2001, then by thedecree n°2002-254 of February 22, 2002, is a public establishmentof an industrial and commercial nature (EPIC), under the joint
authority of the Ministers of Defense, the Environment, Industry,
Research and Health.
IRSN employs more than 1,500 specialists, including engineers,
researchers, doctors, agronomists, veterinarians and technicians,
experts in nuclear safety and radiological protection and in thecontrol of nuclear and sensitive materials
The Institute exercises specialist and research assignments in thefollowing fields:•

nuclear safety;•

safety in transporting radioactive and fissile materials;•

protection of man and the environment against ionisingradiation;•

protection and control of nuclear materials;

Doctrine & synthèse•

physical protection of facilities and transport of radioactive
and fissile materials.

Editions property of IRSN
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Web site : www.irsn.org

This document may not betranslated, adapted or reproduced
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whatsoever without written
authorization. For further
information, please contact:

IRSN
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FranceFax : +33 1-58-35-73-82

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Forward
The Institute for Radiological Protection and Nuclear Safety
conducts research programmes and studies on nuclear andradiological risks; it is responsible for public service activities in theprevention of these risks and provides technical support to thecompetent public authorities in nuclear and radiological protection
safety and security. In this respect, the Institute is called on todevelop a position on a certain number of scientific and technicalissues.
Under its policy of transparency and its desire to make high-quality
information available to all partners and stakeholders for use indeveloping their own views, IRSN publishes doctrine and summary
documents that present the Institute's position on a specific subject.
IRSN specialists prepare these documents, if appropriate inconjunction with outside experts, which are then submitted to aquality assurance validation process.
They reflect the IRSN position on the day of their publication on its
internet site. This position may reviewed in the light of progress inscientific knowledge, changes in regulations or a need for more indepth discussion of the subject to respond to an internalrequirement or external requests.
This document may be used and quoted freely on condition thatthe source and publication date are mentioned.
Comments are welcome. They may be sent to the address
indicated alongside, quoting the related document.

www.irsn.fr

Doctrine & synthèse
IRSN
BP 17
92262 Fontenay aux Roses
cedex
FranceFax : +33 (0) 1 58 35 79 71

doc.syn@irsn.fr

Jacques Repussard
Director General© IRSN/2006 --- All right reserveddoc reference
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Jean-Claude Nénot
Annie Sugier

Adviser to the Director of Strategy,
Development and External
Relations Division
Strategy, Development andExternal Relations Division
Member of the International Commission
on Radiological Protection© IRSN/2006 --- All right reserveddoc reference
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Abstract
The present document provides a brief description of the nine
reports discussed during the 54th session of the United Nations
Scientific Committee on the Effects of Atomic Radiation(UNSCEAR) . This session was held in May 2006 and is part of awork cycle covering the period from 2003 to 2007.
Created in 1955, UNSCEAR periodically compiles reports which
provide an exhaustive and international summary of scientific dataon ionising radiation.

UNSCEAR:
United Nations
Scientific Committee
on the Effects ofAtomic Radiationwww.unscear.org

The reports discussed during the Committee's 54th session coversubjects as varied as sources of radiation, exposure of the public andworkers, exposure due to radon, medical exposure, effects ofradiation on humans and non-human biota, physiopathology ofradiation effects, mechanisms and epidemiology of radiationinduced carcinogenesis, mechanisms of radiation effects, noncancer
health effects, effects of radiation on the immune system, and nontargeted and delayed effects. These reports are practically all in finalor near-final form, but some have not yet been completed.

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Preface
Although this summary report is published in the IRSN's Doctrine
and Summary Reports collection, it does not aim to define theInstitute's positions but rather to present the main themes of the
UNSCEAR reports for the period 2003–2007.
Another novel feature of this report is its publication before that of
the UNSCEAR reports themselves. The objective is to help those in
the radiological protection field stay informed of the latest findingsof international authorities such as UNSCEAR. The IRSN's efforts
have met with the approval of the UNSCEAR Secretariat.
The IRSN also fulfils its duties as a public advisory body open tosociety's various stakeholders by disseminating the information its
experts gain through collaborative projects with international
authorities.
Radiological protection standards are based on scientificunderstanding of the effects of radiation on humans and theenvironment. Given the complexity of this field and its relationships
with disciplines as varied as medicine, biology, chemistry, physics
and radioecology, it is essential that the international community
regularly review new developments in the understanding of sources
and risks. The mission of the United Nations Scientific Committee
on the Effects of Atomic Radiation is to carry out such reviews andpresent its findings to the General Assembly of the United Nations.
For the preparation of its reports, the Committee relies on
consultants selected by its Scientific Secretariat. These reports are
discussed by delegations from 21 nations during UNSCEAR's annual
meetings. They are published at the end of a work cycle lastingroughly five years.
The current cycle (2003–2007) is not yet completed, but the nine
reports discussed during UNSCEAR's 54th session in May 2006
provide a solid basis for a brief description of the major themes
explored in the upcoming publications.

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Contents
1/ Introduction

9

2/ Finalised reports

10

2/1 Sources-to-effects
workplaces

assessment

for

radon

2/2 Epidemiological studies of radiation and cancer

in

homes

and
10
11

2/3 Epidemiological evaluation of cardiovascular disease and other16
noncancer diseases following radiation exposure
2/4 Effects of ionising radiation on the immune system

19

2/5 Non-targeted and delayed effects of exposure to ionising22
radiation

3/ Reports in progress28

3/1 Effects of ionising radiation on non-human biota

28

3/2 Exposures from radiation accidents

29

3/3 Exposures of the public and workers to various sources of29
radiation
3/4 Medical radiation exposures

4/ Conclusion

32

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9/38• 1/ Introduction

1/

Introduction
Each subject is presented as a status report on the latest scientificdevelopments. The reports had already undergone discussion andanalysis during earlier sessions and some date back several years.
The current versions are therefore extremely detailed, validated by
the representatives of the various member nations of UNSCEAR.
Five reports were presented in near-final form; publication isplanned for 2006, or 2007 at the latest. They discuss: 1/ the effectsof radon, 2/ epidemiological studies of radiation-induced cancer, 3/
noncancer health effects of radiation, 4/ effects of radiation on the
immune system, and 5/ non-targeted and delayed effects ofradiation. Four other reports were presented in draft form but are
actually revised and improved versions of documents alreadypresented or discussed during earlier sessions; they should be
published within the next two years. They discuss: 1/ the effects ofradiation on non-human biota (publication planned for 2008), 2/
radiation accidents (2007), 3/ sources of exposure for the public andworkers (2007), and 4/ medical exposures (2008).

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2/

Finalised reports
2/1

Sources-to-effects assessment for radon inhomes and workplaces
This voluminous report has been presented to the members of
UNSCEAR on a regular basis for several years. The current format is
identical to that of the 2004 version, with the same clear, logicalapproach. The document is exhaustive, constituting anencyclopaedia of studies on the effects of radon. However, thesection on experimental studies is quite underdeveloped and refers
to the American report NCRP 65 (2004) , also on radon risk. Thisgap can be explained by the report's objective, which is to assess
the risk in humans, a difficult task to accomplish using animalmodels alone. The report reviews radon measurements and therelated risks, as well as assessing study findings. It successively
examines the studies carried out on 1/ miners exposed to radon riskin North America (United States, Canada, Newfoundland), Europe(France, the former Czechoslovakia, Sweden), China and Australia;
and 2/ populations in the United States, Canada, Europe (Sweden,
Finland, France, United Kingdom, Germany, Italy, Czech Republic,
Austria) and China. The most detailed studies concern United States
Colorado plateau uranium miners; Ontario, Saskatchewan and Port
Radium Canadian uranium miners; the first Czech miners ofpitchblende; Swedish iron miners; uranium miners in the former East
Germany; French uranium miners; fluorspar miners in
Newfoundland and Chinese uranium miners. French authors are
duly cited: early specialists such as Jammet, Pradel, Chamaud andZettwoog (IPSN/CEA/COGEMA) are cited 7 times and current
experts are cited more than 20 times: Tirmarche, Laurier et al.
(IRSN) 14 times and Monchaux et al. (CEA/DSV) 7 times.
Regrettably, the report lacks a chapter on risk modelling, but there
are considerable improvements compared with the previous version,
especially with regard to the epidemiological studies on theconsequences of residential radon exposure, which now include
American and European case-control studies. This addition

Report R.654:
Sources-to-effects assessment
for radon in homes andworkplaces

NCRP 65:
National Council on Radiation
protection and measurements.
Evaluation of occupational andenvironmental radon risk.
NCRP SC 65, 2004

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facilitates comparison across the uranium miner studies and the
population studies, which demonstrate a satisfactory level ofconsistency: the relative excess risk for developing lung cancer isestimated to be 0.16 per 100 Bq m-3 with an uncertainty factor of 3,
higher or lower. This estimate is very close to the one given in the
BEIR VI report , i.e. 0.15 per 100 Bq m-3. The contributions ofMargot Tirmarche (IRSN) in this area were very warmly
acknowledged by the consultant. As he rightly pointed out, there
are unfortunately no studies on miners or the public that take the
distribution of individual doses into account, a consideration which
would have undoubtedly refined risk estimation. Smoking is asignificant confounding risk, since 90% of the risk related toresidential radon exposure is linked to smoking. Because the experts
were divided as to whether smoking has a multiplicative effect or a
sub-multiplicative effect on the risk of radon-induced lung cancer,
the report does not take a position on this issue.

BEIR VI:
Committee on the Biologicaleffects of Ionizing Radiation.
The health effects of
exposure to indoor radon.
National Academy of
Sciences (USA), National
Research Council. National
Academy Press, Washington,
1999

This report was presented in its final form, notwithstanding a few
minor additions and corrections suggested during the session. A
general conclusion will also be added. It should be published before
the end of 2006.
2/2

Epidemiological studies of radiation andcancerThis thick report --- including detailed tables and figures as well as
technical appendices on methodology, risk measurement andmodelling --- complements UNSCEAR's previous reports. It presents
the findings of studies not previously analysed or summarised; itallows risk factors to be assessed for individual organs and tissues.
Compared with the previous document published in 2004, thisreport is exhaustive, providing readers with numerous data sources
and results. Amongst the populations particularly vulnerable to therisk of radiation-induced cancer but not included in previous
versions, the following merit particular attention:

Report R.658:
Epidemiological studiesof radiation and cancer•
Workers at the Mayak nuclear complex, including several
people who incorporated plutonium, usually in moderate quantities.
Cancer mortality was studied in a cohort of 21,500 workers,
including 26% women. The cohort workers were employed at thecomplex between 1948 and 1972, with a cumulative average doseof 0.8 Sv. This population has received high-quality follow-up since1977. Amongst the 7,067 deaths observed, 1,730 were due to solidcancers and 77 to leukaemia. Plutonium was found in the organs of© IRSN/2006 --- All right reserved/38

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668 people who had died from cancer. Lung and stomach cancer
are the predominant causes of death. Excess relative risk is 0.30 Gy-1
for the lung, liver and skeleton. The dose-effect relationship isslightly concave at higher doses, expressing an inversely
proportional risk factor at these doses. The level of risk observed inthis study is markedly lower than that observed for the Japanesesurvivors of Hiroshima and Nagasaki. This finding may be due todose uncertainty, plutonium contamination of the lungs (sufficientin some cases to produce fibrosis) or to the fact that the most
exposed individuals were autopsied more frequently (and thus
received more reliable diagnoses). Moreover, neither the age at
initial exposure nor the time elapsed after exposure appears to berisk-modifying factors, even though risk has been shown to decrease
with age.
•
Populations living along the Techa River (Southern Urals),
exposed to huge quantities of radioactive effluents which theformer Soviet Union carelessly dumped in the river during thenuclear weapons race. Scientists began assessing internal exposurein 1951 using autopsy sample measurements. In 1959 they began
using whole body countings as well as in vivo measurements onteeth. Approximately half of these populations were assessed forindividual strontium-90 body burdens (using yttrium-90
measurements). However this is an ecological study, based on
measurements of the average internal and external exposures for all
residents of a given village. There is also a great deal of dose
uncertainty and most importantly, a very high degree of variation indose distributions (at least two orders of magnitude). Consequently,
the results of this study should be interpreted with caution. For
example, excess relative risk for solid cancers varies with untypicalparameters, such as age at initial exposure and attained age. This iscontrary to the findings for Hiroshima and Nagasaki survivors.
•
Populations living around the Semipalatinsk test site
(Kazakhstan). Ten villages were exposed to fallout from 122
atmospheric explosions conducted between 1949 and 1962. The
study followed individuals born before 1961. The findings are notconsistent with other studies considered as reliable: relative excess
risk for these populations is 0.81 Sv-1 for all solid cancers, 0.95 Sv-1
for stomach cancer and 1.76 Sv-1 for lung cancer. Risk is shown toincrease with age at exposure, which is contrary to study findingsfor Hiroshima and Nagasaki survivors. The question remains as towhether this untypical relationship results from ecological bias, orwhether it points to the difference between the acute exposure of© IRSN/2006 --- All right reserved/38

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Japanese survivors and the prolonged exposure around Soviet testsites.
•
Cohorts of workers employed in the civil nuclear industry(International worker study), which bring together 407,391 subjectsof all different nationalities and backgrounds. Amongst them,
190,000 were excluded from the study for various reasons: they had
not been employed in one or several installations for a year or more,their doses had not been recorded or they had received internal or
neutron exposure. The cohort accumulated 5.2 million person-years.
The average individual dose was 19.4 mSv. The distribution of
cumulative doses indicates that 90% of subjects received less than
50 mSv and less than 1% of subjects received more than 500 mSv.
Amongst the deaths recorded for all cohorts, 6,519 were due tocancers and 196 were due to leukaemia. According to the main
study, conducted by the International Agency for Research on
Cancer (IARC) , relative excess risk is 0.97 Sv-1 for solid cancers
and 1.93 Sv-1 for leukaemia. The risk estimate for solid cancers is 8
times higher than that published in the Japanese Life Span Study(LSS) , even after reduction by a factor of 2 to account for low
doses and low dose rates. Lung cancer (1.86 Sv-1) has a strong
impact on the rate of solid cancers. The risk of cancer --- excluding
leukaemia, lung cancer and pleural cancer --- is only 0.59 Sv-1.
However, because cancers attributable to smoking represent an
relative excess risk of 0.21 Sv-1, the risk for noncancer radiationinduced respiratory disease is 1.16 Sv-1, whereas the risk for chronic
obstructive bronchitis and emphysema is 2.12 Sv-1. The conclusion
is that the confounding factors arising from smoking, when taken
together, may partially, but not totally, explains the increased risk ofmortality for all cancers, except leukaemia. If the cohorts are
considered separately, we see that the Canadian worker study has astrong impact on relative excess risk for solid cancers. Although thisstudy accounts for only 400 cancer cases overall (6.1%) and theaverage individual dose is comparable to that of all cohorts taken
together (19.5 mSv versus 19.4 mSv), excluding it from the overall
study reduces the risk to 0.58 Sv-1. Moreover, the risk for lungcancer is abnormally high in the Canadian study, i.e. 3.1 Sv-1, as is
the number of deaths from such diverse causes as parasitic andinfectious diseases (4.9 Sv-1), cardiovascular diseases (2.3 Sv-1) and
accidents (8.8 Sv-1). These surprising figures are most likely the
result of several unidentified biases in the study. These biases taintmuch of the overall study, which involves 15 countries.

IARC:
International Agency for
Research on Cancer: IARC
Study Group on cancer risk
among nuclear industry
workers. Direct estimates ofcancer mortality due to low
doses of ionising radiation: an
international study. Lancet Vol
344 -October 15, 1994, 10391043

D.L. Preston, Y. Shimizu, D. A.
Pierce, A. Suyama and K.
Mabuchi. Studies of mortalityof atomic bomb survivors.
Report 13: Solid cancer andnon cancer diseases mortality:
1950-1997. Radiation
Research, 160, 381-407, 2003•
American radiology technicians, a population of 146,000
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between 1926 and 1982. In 1997, amongst the 12,624 deaths in acohort of 90,305 subjects, cancer was the cause of death in 2,651
cases. Dose reconstruction is underway but not yet available. The
results of the study are still fragmentary but suggest that the
number of years spent working with radiation is not associated withan increased risk of cancer. There does seem to be a trend towards
excess mortality in general and excess breast cancer in particular.
However there are serious doubts concerning the study's core data,
and therefore its robustness. This is due to confusion between job
entry dates and birth dates, dose uncertainty, the lack of correction
for geographic factors, etc.
•
Chinese radiologists and technicians; their cases were
documented between 1950 and 1995. This population included
27,011 people scattered across 24 Chinese provinces. There are nodose data prior to 1985, but with retrospective assessment using
biological methods, the cumulative average individual dose isestimated to be 758 mGy for those who worked before 1960, 279
mGy for those who worked between 1960 and 1969, and 83 mGyfor those who worked between 1970 and 1980. An excess isobserved for solid cancers taken together, with a relative risk of
1.19, and for leukaemia, with a relative risk of 2.17. Excesses arealso observed for breast cancer (relative risk of 1.34), skin cancer
excluding melanoma (4.05), oesophageal cancer (2.65), liver cancer(1.20), lung cancer (1.20) and bladder cancer (1.84). The age at
exposure seems to be determinant for lung and thyroid cancers.
However, these results must be interpreted with caution because
the calculations were not carried out in a very rigorous manner,
especially those for the control group.
•
Aircraft personnel are exposed to relatively significant doses
which were frequently as high as 6 mSv per year, but lifetime doses
do not exceed 80 mSv. There is a substantial neutron component(25% to 50 %). Three studies are of particular interest; the firstincludes the personnel of several European airlines and the othertwo focus on pilots. The parameters differ for each study: timespent working, time-of-flight at high altitudes and exposure level. In
the first two studies, an excess of melanomas is observed in malepilots, whereas this excess is not observed for women in the firststudy (the second study only involves men). This specific excess risk
was not observed in the third study. There is a slight trend acrossthe three studies towards an excess relative risk for all cancers. Thisrisk increases with dose; for doses above 25 mSv, the relative risk is
0.74. Dose uncertainty is due to the fact that the level of solar
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correlation was found between increased risk and time spentworking, there is considerable doubt surrounding the aetiology ofskin diseases attributed to radiation.
•
The studies of specific risk factors are particularly detailed
and focus on over 20 organs and tissues: salivary glands,
oesophagus, stomach, small intestine, colon, rectum, liver, pancreas,
lungs, bone and connective tissue, skin, breast, uterus, ovary,
prostate, bladder, kidney, brain and central nervous tissue, thyroid
gland, lymphatic system (for non-Hodgkin's lymphoma andHodgkin's disease) and bone marrow (for multiple myeloma andleukaemia). Eight of these organs were not considered in the
UNSCEAR report presented in 2000 . The current findings suggestthat it is impossible to define a single value for either overall risk or
specific risks, mainly because of the variability in the methods used
to project risk. In general, risk uncertainty for a given organ orcancer is greater than that for total cancer. As of this writing, thefollowing points seem firmly established:
1/ For each of the solid cancers, relative excess risk and excess
absolute risk are proportional to a product of powers of time since
exposure and attained age;

UNSCEAR 2000: United
Nations ScientificCommittee on the Effects ofAtomic Radiation. Report to
the General Assembly with
Scientific Annexes. Vol. II:
Effects, Annex I:
Epidemiological evaluationof radiation-induces cancer,
United Nations, New York,
2000

2/ Relative excess risk for leukaemia is also proportional to a
product of powers of age at exposure and attained age, whereas
absolute excess risk is proportional to a power of time since
exposure;
3/ When these risk models are applied to any of the core study
populations (in China, Japan, Puerto Rico, United States, United
Kingdom), the lifetime risk (an average of values for both sexes) is
estimated to be between 4.3% and 7.2% for a dose of 1 Sv; thesevalues may vary depending on the population and the models used ;4/ These estimates are slightly lower than those previously
reported by UNSCEAR and other organisations. This reduced risk
can be explained by the new dosimetry for the Japanese A-bomb
survivors and by the use of new models ;5/ These risk estimates involve an uncertainty factor of 2, higher
or lower; they may be 50% lower in the case of prolonged exposure,which is also marred by an uncertainty factor of 2, higher or lower ;6/ The cancer risk is markedly greater for children --- as much as 2
or 3 times higher --- compared with the risk for a mixed-age
population ;7/ The study of cancers in the Japanese A-bomb survivors
produced findings consistent with a linear (or linear-quadratic)
dose-effect relationship. Consequently, the linear extrapolation of© IRSN/2006 --- All right reserved/38

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the risk value at 1 Sv (acute dose) can be used to obtain an initial
estimate of low-dose risk ;8/ Finally, for site-specific cancers the findings presented in 2000
remain unchanged or differ only slightly.
The results not reported in earlier reports involve specific systems,
organs and diseases:
1/ The potential for developing cancer varies widely for thedifferent organs of the digestive system. Further studies are needed
to clarify the possible relationships between radiation-induced livercancer and other diseases, such as viral infections (hepatitis C) andcirrhosis;
2/ The pancreas seems relatively resistant to radiation-induced
cancer ;3/ The lung is very sensitive to radiation, as shown by: studies of
the Japanese survivors of Hiroshima and Nagasaki, patients exposed
for medical reasons, populations around the Mayak site, etc.
Relative excess risk appears to be higher for women and does notdecrease with age. There are no studies demonstrating the
carcinogenicity of radiation at low doses and low dose-rates.
Radiation's cancer-inducing ability has an additive effect on that ofsmoking; in some cases the effect is multiplicative or even greater ;4/ The breast is a very sensitive organ for which there areaggravating factors, such as predisposition to cancer linked togenetic or reproductive parameters ;5/ The uterus and the kidney are relatively resistant to radiation;uterine cancer is only reported at doses of several tens of Gy or
higher ;6/ The thyroid gland is amongst those organs which areparticularly sensitive to radiation; for children the relative excess
risk persists throughout life, but there are studies suggesting it may
decrease 20 years after exposure.
2/3

Epidemiological evaluation of cardiovasculardisease and other noncancer diseases
following radiation exposure
The main criticism of the 2004 version was that its title(Epidemiological evaluation and dose response of diseases otherthan cancer) gave the impression that it described a number ofReport R.657:
Epidemiological evaluationof cardiovascular disease
and other noncancer
diseases following radiation
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noncancer radiation-induced diseases affecting various organs andtissues. In fact, the report only addressed cardiovascular diseases
caused by radiation exposure and made no mention of othersystems and organs known or believed to be targeted by noncancer
radiation-induced diseases, such as the digestive and respiratory
systems, the lens of the eye and the thyroid gland. Although the
document has been considerably substantiated since 2004, thesame criticism applies to the 2006 report. The Committee therefore
decided to change the title to reflect the focus on cardiovasculardiseases. The reasons for overlooking the other systems and organs
are well founded: 1/ because these other diseases are only rarely
fatal, unlike cardiovascular diseases, the data lack robustness andare difficult to use; 2/ there is a substantial number of diseases for agiven system or organ; 3/ the number of biases and confounding
factors for each disease is particularly high; and 4/ numerous otherrisk factors, not to mention socio-economic factors, are harder todefine than for the cardiovascular system. However, thesearguments are not valid for cataracts and noncancer thyroid
diseases. There are now reliable data on these conditions,particularly for the workers and populations affected by the
Chernobyl accident. These data were analysed in the UNSCEAR
Chernobyl report and therefore are not reviewed in the report underdiscussion. Although this report may give the false impression thatcardiovascular diseases predominate amongst noncancer radiationinduced affections, the document is very satisfactory, in terms ofboth form and content. It explains the selection criteria for thecohorts and discusses the healthy worker effect, the quality ofmortality data (overestimation of noncancer diseases due to errors
in determining cause of death), confounding factors due to themultiple causes of cardiovascular diseases, and considerable
variations based on lifestyle, location and socio-economic status.
The report mentions the biases apparent in certain publications.
These biases are due to the fact that epidemiological studies on theeffects of doses below the threshold values for deterministic effects
have so far focused primarily on radiation-induced malignant
diseases. The current report leaves out the chapter on the
Hiroshima and Nagasaki survivors --- a noteworthy improvementcompared with the 2004 report. As a result, diseases are categorisedby type and not by cohort origins; therefore the diseases observedin the Japanese survivors are now considered together with those of
the other cohorts.
The report's conclusions are particularly relevant to radiologicalprotection. Noncancer radiation-induced diseases affecting the
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been considered part of the family of deterministic effects, withrelatively high dose thresholds (4---5 Gy depending on the disease
and the affected organ), but it now appears that these diseases canbe induced by lower doses. This point is underscored by the Life
Span Study (Japanese A-bomb survivors) in particular. It points tothe need for new studies on populations exposed to relatively low
doses. The challenge is that many of the existing studies (almost50%) cannot be applied to noncancer effects. Most of the data forthese effects come from cohorts of patients irradiated for medical
reasons (treatment of benign diseases or diagnostic radiology
examinations); cardiovascular disease was the predominant
complaint amongst these patients. For example, the risk of coronary
heart disease increases when the heart is exposed to a dose of 1.6--3.9 Gy. Given that the findings of mortality studies are consistent
with those of morbidity studies, noncancer effects are all the morecredible. The biological mechanisms that cause such diseases
remain unknown. The report suggests mechanisms involving
primary damage to the microvessels of the pericardium andmyocardium, atheromatous lesions of monoclonal origin, andinflammation, but is unable to provide convincing evidence. In
conclusion, the report stresses the need for further studies, in thefields of epidemiology and biological mechanisms.
The report was deemed to be in near-final form and should thus be
published rapidly. It will contain no animal data, because it focuses
exclusively on epidemiological studies. The authors must now add
the final conclusion, which will highlight the following points:
1/ Previously the risk of cardiovascular disease was linked todoses above 40 Gy (irradiations of the mediastinum for Hodgkin's
disease), but there are now data to suggest risk at lower doses,
around 30---35 Gy for adults and 15---25 Gy for children. For evensmaller doses (patients irradiated for ankylosing spondylitis with anaverage dose to the pericardium of 2.5 Gy) the number ofcardiovascular deaths is higher than for patients with the samedisease but no exposure. However, it is impossible to draw solid
conclusions because of the low excess risk ;2/ Risk varies with age at exposure and the time elapsed since theevent, but it may persist for three or four decades. Risk data frompatient studies are consistent with follow-up results for thesurvivors of Hiroshima and Nagasaki ;3/ It would be interesting to study the cohorts of healthprofessionals exposed in the early 20th century. Unfortunately, thelack of dosimetric data would make any definitive conclusions
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for these populations it is the existence of several unidentified
confounding factors that weakens the studies ;4/ For diseases other those affecting the cardiovascular system,
there are data from the follow-up studies of Hiroshima andNagasaki survivors suggesting a causal relationship with doses of 1--2 Gy or lower. However, this conclusion is less robust than for
cardiovascular diseases because of the limited data, the wide rangeof diseases, the various aetiologies and pathological mechanisms,
and the multitude of confounding factors ;5/ The Committee underscores the fact that the report's
conclusions may have socio-economic consequences; in many
countries it has become an established practice to seek
compensation for cancers and other diseases attributed to radiation
exposure, and there are numerous claims of this sort.
2/4

Effects of ionising radiation on the immune
systemThis report is a follow-up to the 2004 report, in which numerous
sections required further development. It offers a very technicalreview aimed at specialists, despite a clear effort to make it
accessible to readers with a limited understanding of the immune
system. This study is particularly interesting because the primaryfunction of the immune system is to protect against infections andcancer through a system which recognises antigens. Response
quality depends on four parameters: memory, specificity, diversity
and the ability to discriminate. The report reviews the components
and parameters that play a role in the immune response. The main
cells involved are lymphocytes --- B cells and T cells --- which maturein the bone marrow and the thymus. B cells govern the humoral
response whereas T cells play a central role in cellular responses.
Transported by the circulatory system, mature lymphocytes clusterin the lymph nodes, the spleen and the other tissues of thelymphatic system. As for the skin, its ability to block and defend
against pathogenic agents can be either innate or acquired. Finally,
immunosenescence is a complex phenomenon resulting from thedysregulation of the immune system rather than an overall decline.
According to the studies, both high sub-lethal doses and low dosesof radiation appear to significantly reduce immune capacity acrossall parameters of the immune response. This response depends on
the total dose, but dose rate has little or no impact. This suggeststhat response to high dose rates may be used to predict the effects

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Effects of ionising radiation on
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20• 2/ Finalised reportsof low dose rates, across a wide range of doses and dose rates.
Lymphoid cells and tissues are particularly sensitive to high LET ,radiation, even at relatively low doses; the negative effects persist
long after absorption.
Exposure of experimental animals to prolonged low dose radiation
results in adaptation of the haematopoietic system, which isnormally very sensitive to radiation but under these conditions
develops a relative resistance to it. This modification affects
progenitor cells, and recovery may be incomplete. There is a great
deal of evidence that this type of exposure activates immune
functions: under the same exposure conditions, inhibition ofmalignant tumour growth, of metastasis and of carcinogenesis in
general have been observed. Furthermore the adaptive response is aphenomenon observed in numerous systems and appears linked to
the reduced apoptosis (programmed cell death) observed in thehaematopoietic system following exposure to high doses.

LET:
Linear energy transfer, whichmeasures the density ofionisation along the path of acharged particle with a given
energy; it is expressed as theaverage energy transferred to
the local surroundings by theparticle, divided by the distancetravelled.

The short-term effects observed in the Japanese A-bomb survivors
mainly involved acute bone marrow exhaustion related to cell deathand proportional in severity to the dose received. Such effects arereversible within several months. The most noteworthy
consequences are quantitative and functional abnormalities in T
and B cells in subjects exposed to doses above 1 Gy. However, there
appears to be no quantitative or functional effect on naturalimmunity as there is on adaptive immunity.
Abnormalities of all sorts were detected in members of the general
population exposed to radiation as a result of the Chernobyl
accident, but they are difficult to interpret because of the many
confounding factors. The data vary as a function of studied
population, dose, dose distribution over time, type of exposure(external and/or internal) and time elapsed since exposure. Shortand long-term effects were found in children living in theparticularly contaminated zones around the site. They involved
functional modifications of T and B cells, as well as changes in thebiosynthesis of the immunoglobulins in serum and saliva. Some ofthese phenomena were dose-dependent. The immune system is
implicated in the pathogenesis of thyroid diseases observed in somevictims; the combination of radiation and antigenic phenomena
apparently provoked an autoimmune response. Stress-related
hormonal reactions, respiratory diseases and chronic infections may
have also contributed to the various immunological disorders
observed in the populations affected by the accident. Among theworkers who helped clean up the site (the liquidators), responses
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21• 2/ Finalised reports(firemen and rescue workers involved during the accident received
doses of 0.5-9 Gy; those involved in the first days after the accident
received doses of 0.1---0.5 Gy).
The findings in populations as diverse as the Japanese A-bomb
survivors, the persons affected by the Chernobyl accident andvillagers along the Techa River show that the negative effects on
the immune system persist more than 50 years after exposure. The
proliferation of radiation-induced cellular mutations can cause
clonal expansion, affecting haematopoietic stem cells, specificprogenitor cells and mature T cells in particular. It appears thatclonal expansion, which is not especially dangerous, emerges a few
years after exposure and most likely signals an attempt to repair thedamage to the immune system. Epidemiological studies appear tosuggest that radiation-induced modifications of immune capacity
may increase the risk of developing those diseases observed in older
people. Therefore radiation may accelerate immunosenescence, likenatural aging, by disrupting the homeostasis of T cells. Apoptosis isessential to maintaining normal cellular homeostasis in the immune
system. The bystander effect, the adaptive response and genomic
instability have been shown to play a role in the immune responseto radiation. However, their potential health consequences havebeen neither explained nor demonstrated. Nonetheless, lowered
immune defences can increase the risk of cancer by affecting
reactions which target malignant cells. Moreover, individual genetic
susceptibility to radiation, which has been demonstrated, is often
associated with functional damage to the immune system.
The main conclusions of the report are as follows:
1/ The immune system is undoubtedly one of the body's mostcomplex systems, involving numerous cells in the various organs
and tissues where stem cells mature. Immune cells communicate
with help from cytokines --- soluble molecules which stimulate
cellular proliferation and differentiation.
2/ The data examined in the report suggest that radiation
exposure often results in immunosuppression, particularly after highdoses. This phenomenon is related to the fact that lymphocytes arehighly sensitive to radiation. In addition to these cytotoxic effects,
radiation can trigger a "danger signal", which can in turn affect thecellular-level immune response. Therefore, radiation exposure
shouldnotbecategorised
withcytotoxic
agents(immunosuppressive agents), but should instead be considered an
immunomodulatory agent.

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3/ This immunomodulatory action against cancer is now better
known. According to conventional theory, malignant tumours may
develop if immune surveillance fails to detect them, due either toreduced expression of tumour antigens, or to changes in the
immune response. It now appears that immune-related tumour
promotion may also be tied to persistent low-level infections, theactivation of immature immune cells or antibodies which block
cellular activity.
4/ There is disagreement about the effects of low doses (below
200 mGy) and low dose rates (below 100 mGy h-1). In humans,
cellular irradiation often produces irregularities interpreted as
reduced immune capacity; certain studies suggest that prolonged
exposure may result in an adaptive response.
5/ Several questions should be explored in greater depth. They
mainly concern: the effects of low doses and low dose rates
compared with those of moderate and high doses, the combined
effects of irradiation and other agents, the effects of external
exposure compared with those of internal exposure, the relationshipbetween immunomodulation and cancer, disruptions in T cellhomeostasis, the relationship between immunity andcarcinogenesis, and the effects of aging on immune function andthe inflammatory response.
2/5

Non-targeted and delayed effects of exposure
to ionising radiation
Compared with the previous report (R.638, 2004), the current
document is slightly better documented, but the differences are notvery significant. In 2004, the subject was truly novel, because inearlier publications and draft publications it had only beenaddressed in a fragmented, incomplete fashion. This report's strong
point is that it is practically the only document focusing on
phenomena described relatively recently and in need of further
investigation and clarification, particularly because of the potential
repercussions on radiological protection standards. The term "nontargeted effects" encompasses effects with various mechanisms, butthey share a common characteristic: they are not related to energy
deposit in cell nuclei, which until recent years was the central
dogma of traditional radiobiology. Consequently, the carcinogenic
effects are somehow tied to mutagenic and clastogenic risks. These
effects were recently described in an NCRP draft reporton risk

Report R. 659:
Non-targeted and delayed
effects of exposure to ionisingradiation

National Council on Radiation
protection and Measurements.
Extrapolation of risks from
nonhuman experimental
systems to man. NCRP Draft
Report SC 1-4, October 2003

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extrapolation. Current knowledge is based on in vivo and in vitro
findings.
Genomic instability is well known and has been described in theliterature for several years. It involves increased changes in the
genome and is the first critical step in the development of certain
radiation-induced cancers. This concept encompasses both thechromosomal instability of cells not directly irradiated but situatedin a radiation-exposed environment, and the instability of cells
descended from non-irradiated stem cells. It appears likely thatsignals from irradiated cells can stimulate chromosomal
rearrangements in cells not present at the time of irradiation.
Various observations in humans have helped clarify the relationshipbetween irradiation and genomic instability: 1/ instability is found invitro in cultures of irradiated human lymphocytes (from victims of
the 1994 radiation accident in Estonia), 2/ chromosomal
aberrations found in peripheral blood lymphocytes persist in the
Sellafield plutonium workers (undoubtedly due to a selection ofirradiated precursors in bone marrow), 3/ a high rate (19/20) ofgenetic mutations (TP53) is observed in former patients injectedwith thorotrast, 4/ instability is observed in patients who develop
second cancers following radiotherapy for bilateral retinoblastoma,and 5/ chromosomal aberrations and rearrangements are observedin the Hiroshima and Nagasaki survivors who developed acute
myeloid leukaemia following exposure to doses above 2 Gy. In
contrast, no cellular aberrations were observed in 18 patients
exposed to a total of 35–80 Gy administered in a fractionatedmanner. Certain observations suggest that genomic instability plays
a non-negligible role in the development of cancer and support theconclusion that persistent instability may strongly influence thedevelopment of leukaemia in humans.
The bystander effect is employed in a relatively restricted sense in
the report, which states that the bystander effect describes thecapacity of cells affected by an external agent to transmit any
manifestations to other cells that are not directly targeted or thatare capable of expressing the damage. This definition implies thatthe bystander effect results from a signal produced by a cellinteracting with a non-irradiated cell, rather than radiation-induced
modifications in the culture medium. Current knowledge is primarily
based on in vitro experiments. The bystander effect was first
demonstrated for alpha emitters and charged-particle microbeams.
When these forms of irradiation are focused selectively on a given
cellular component, inducing the secretion of one or several
substances, they can produce various effects: 1/ stimulation of© IRSN/2006 --- All right reserved/38

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apoptosis, reducing clonal capacity; 2/ increased mutagenesis andhigher rates of neoplasmic transformation; or 3/ induction of
genomic instability in non-irradiated cells. Once irradiated cells aretransferred to the culture medium, increased cell death is observed.
There is also a decrease in clonal efficiency as well as an increase inneoplasmic transformation and genomic instability. Several
experiments using low-LET radiation are currently underway; thefindings are similar. For example, the irradiation of humankeratocytes using 60Co produces a bystander effect for the dose
range of 0.01–0.5 Gy and relatively constant independently of thedose level; above 0.5 Gy, cell death is as much a direct result ofirradiation as it is a bystander effect. In contrast, cellular responses
other than cell death (e.g. proliferation) were observed in cultured
human fibroblasts propagated from cells irradiated with an alphaemitter. This contradiction is difficult to explain. Nonetheless, atleast in vitro, bystander effects can modify cellular response. It
remains to be seen whether these effects, which are observed in
non-irradiated cells, are determinant in the in vitro response ofirradiated cells as well as the in vivo response of irradiated and nonirradiated cells. The few in vivo experiments have been very specificin scope – e.g. formation of chromosomal aberrations, aetiology of
micronuclei, embryonic development, regenerative capacities,
activation of macrophages and tumour growth - and the findings
are difficult to interpret. However it has been shown that the
number of liver cancers is not related to the number of cells
irradiated. This might be explained by an "amplification" of thebiological efficiency and thus more cells exteriorising the harmful
effects than the number directly exposed to radiation. This effectpredominates at low doses, which allow it to produce a complete
cellular response. At this time, the only possible conclusion is thatradiation targets an area beyond the physical limits of the nucleus.
Another unresolved question concerns the relationship between the
bystander effect and genomic instability. Given the similarity of
their consequences, these two phenomena may in fact be
manifestations of a single process within non-irradiated cells. In thiscase, the high rate of genomic instability may be explained bybystander-like phenomena.
Abscopal effects refer to responses in other tissues located far
from the irradiated zone. For example, after partial irradiation of rat
lung, damage may be observed in the DNA of the non-irradiatedlung cells. This type of effect has also been observed in humans
following radiotherapy, either in a single patient (remission ofhepatocellular carcinoma following irradiation of bone metastases)
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remission observed in bone marrow after irradiation of the spleen).
Some authors, after reviewing all the relevant medical literature,
have concluded that it is currently impossible to confirm or reject
the existence of bystander effects and, by extension, abscopal
effects in irradiated patients.
Clastogenic factors have been brought to light by experiments
demonstrating that the plasma of irradiated humans and animals
contains factors capable of harming non-irradiated cells. For
example, children who underwent isolated spleen irradiation later
showed signs of bone marrow damage. Similar damage was also
observed in individuals exposed during the Chernobyl accident andin the Japanese A-bomb survivors, in equal proportions. These
problems, observed for doses of 200 mGy, persist for around 10
years (as long as three decades for certain Japanese survivors).
There is a high degree of individual variability; moreover not
everyone is likely to manifest this type of effect. The precise natureof the so-called " clastogenic plasma factors" remains unknown;
involvement of endogenous viruses, interference with DNA repair
and free radical production have been discussed. At this time, thelast of these hypotheses appears most likely. However, the presenceof "clastogenic factors" in the peripheral blood of some irradiatedindividuals raises the question of whether chromosomal
rearrangement is an accurate biological dosimeter. If the effects
mentioned above are borne out and occur systematically, there
may be important public health consequences. For example, it is not
impossible to imagine that food products irradiated to enhancepreservation could play a role in producing negative health effects.
However, the few animal experiments conducted to verify thishypothesis have not demonstrated any consequences, except for an
increase in polyploid cells (i.e. with more than two sets ofchromosomes) in bone marrow of rats fed irradiated wheat.
Hereditary effects are those observed in the offspring of irradiatedparents (one or both parents exposed). They have been at thecentre of numerous contradictory debates and certain conclusions
are regularly challenged. The subject is particularly well
documented for certain animal species; the effects have been
observed and described and the risk factors evaluated. For humans,
the situation is completely different; to date researchers have been
unable to demonstrate any radiation-induced hereditary effects,
whether in the offspring of cancer victims treated with radiotherapy
and/or chemotherapy, in women irradiated during childhood totreat haemangioma or in Japanese A-bomb survivors (the cohort
included 31,150 children). A recent study on the inhabitants of the© IRSN/2006 --- All right reserved/38

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Mogilev region of Belarus, particularly contaminated by fallout fromthe Chernobyl accident, is an exception because it appears todemonstrate such effects. But it has been severely criticised by
British researchers, who questioned the use of a non-exposed
population in the United Kingdom as the control group for exposedparents in Belarus. It was further noted that other pollutants andviral diseases had been overlooked, and the biological significance of
certain mutations was challenged. The increased risk of cancer inthe offspring of humans irradiated before their children's conception
is equally controversial. The abnormally high incidence of leukaemia
and lymphoma in children whose fathers worked in the reprocessing
facility in Sellafield has been the subject of fierce debate for anumber of years, but cannot be completely dismissed.
The main conclusions of the report are as follows:
1/ The role of non-targeted and hereditary effects in cancer
induction remains unclear ;2/ As for radiation-induced genomic instability, its role ininitiating and mediating genetic modifications, which could induce
genomic damage and thereby facilitate carcinogenesis, is still basedon speculation. This working hypothesis is further tempered by thefact that very high rates of genomic instability are observed both invivo and in vitro and saturation is rapidly reached at low doses.
However, the issue of inherited hypersensibility is far from resolved
and may have important implications;
3/ In the past, most estimates of hereditary risk were based onclassic mutations observed in very large populations of easy-tostudy mammals. Based on recent studies, it does not appear
necessary to modify the quantification of genetic risk proposed inearlier UNSCEAR reports. However, there is absolutely no proof thatradiation-induced transgenerational instability leads to a
proliferation of clinically significant effects in successive
generations. Since UNSCEAR currently supports the position thatfirst generation risk for a number of effects is transmitted tosuccessive generations, the few cases of proliferation do not justify
a modification of current risk estimates;
4/ With regards to the bystander effect, it is included in the risk
estimation because it only affects the exposed organ and because
the associated risk factors involve organs rather than cells ;5/ It is generally agreed that understanding of these effect types--- genomic instability, bystander effects, abscopal effects,
clastogenic factors and hereditary effects --- is far from complete.
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result is more cells manifesting the damage than the number
directly irradiated.
6/ If all types of radiation are shown to systematically induce
these effects, existing radiological protection hypotheses would
underestimate risk, at least for everyday levels of exposure.
However, the remarkable capacity of biological systems to adapt totheir exposure environment, particularly at low doses, should not be
forgotten. Furthermore, the multiple uncertainties and theinconclusive data on the actual consequences of these effects
suggest that current risk estimates for cancer and hereditary effects
should not be modified.
7/

It is essential to reconsider the concepts of dose and target.

8/ It would be advisable to examine direct and indirect effects incombination for modelling radiation-induced carcinogenesis.
9/ Finally, it should be noted that non-targeted effects can beproduced by harmful agents other than radiation.

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•3/ Reports in progress

3/

Reports in progress
3/1

Effects of ionising radiation on non-humanbiotaThis 102-page document is relatively new. It is the follow-up to a1996 report based on data of limited quantity and quality. The
1996 report concluded that radiation exposure caused by humanactivities adds significantly to the impact of natural exposure. The
main activities cited were those involving radon and its progeny(affecting terrestrial environments), polonium-210 (affecting
aquatic environments) and alpha emitters (affecting terrestrial andaquatic environments). In 2005 it was decided that UNSCEAR
should concentrate on assessing the levels and effects of nonhuman exposure, therefore working upstream of the ICRP and the
IAEA, which shape protection policies. The 2006 version of thereport appears to be a relatively exhaustive review of: 1/ themethods used to assess the levels of exposure and results obtained(reference organisms, transfers in terrestrial, aquatic and marine
environments), and 2/ the somatic and genetic effects observed interrestrial plants and in terrestrial, aquatic and marine animals,considered individually or collectively. The report's objective is tocomplement publications on the same subject by otherinternational or national bodies, such as the ICRP (2003) , the
IAEA (2005) , the Chernobyl Forum organised under the aegis of
the United Nations (2005) , FASSET (2004) , ERICA (2003) ,and the Canadian
the United States Department of Energy
authorities . The French UNSCEAR delegation recently proposed
adding a chapter on the biological mechanisms of biota responses
to radiation exposure, which would allow appropriate monitoring
methods to be defined for many species. The French proposal on
which issues to address in this new chapter was well received, but
as the scope seemed too ambitious for the next report, themembers of the delegation were asked to prepare a summary,focusing on 1/ the main parameters affecting biological responses

Report R.662:
Effects of ionising radiation on
non-human biota
ICRP: International Commission on
Radiological Protection. ICRP
Publication 91: A Framework forAssessing the Impact of Ionising
Radiation on Non-human Species.
Annals of the ICRP, Vol. 33(3).
Pergamon Press, 2003

IAEA: International Atomic Energy
Agency. Draft plans of activities on
the radiation protection of theenvironment. IAEA, GOV/2005/49,
24 August 2005

The Chernobyl Forum: Chernobyl’s
legacy: Health, Environmental andSocio-economical impacts andRecommendations to theGovernments of Belarus, theRussian federation and Ukraine.
IAEA, WHO, FAO, UNDP, UNEP,
UN-OCHA, UNSCEAR. IAEA,
Vienna, 2005

FASSET: Framework forAssessment of Environmental
Impact, Final Report. Developed
under EC 5th Framework Program.
Contract FIGE-C

ERICA: Environmental Risk from
Ionizing Contaminants:
Assessment and Management.
Developed under EU 6th
Framework Program. Contract
FI6R-CT-2004-508847, 2003

United States Department ofEnergy. A graded approach forevaluating radiation doses toaquatic and terrestrial biota. DOESTD-1153-2002, US DOE, 2002

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to radiation, and 2/ the importance of understanding these
phenomena when assessing the biological effects. Given that
reproductive change is a more sensitive indicator than mortality,
UNSCEAR believes that for the majority of terrestrial species,
prolonged irradiation at dose-rates below 100 μGy h-1 should not
significantly affect the most exposed individuals. Similarly, foraquatic species the Committee believes that dose-rates up to 400
μGy h-1 should have no harmful effects in a given population.

29•3/ Reports in progress
Advisory Committee onRadiological Protection (ACRP22).
Protection of non-human biota
from ionizing radiation. Canadian
Nuclear safety Commission(CNSC), INFO-0703, March 2003

3/2

Exposures from radiation accidents
This relatively short report is very recent. The objective was to draw
up a list of accidents involving various sources of radiation.
Although the forward clearly states that the document is notintended as an exhaustive inventory, it seems odd that some severe
accidents are not included while several others with little impact on
the victims, society and/or the environment are discussed in detail.
It is of course impossible to provide a complete overview of allaccidents, especially since the definition of the term "accident"
remains vague, but the radiation sources and their activities foundin the report might give a false idea of the distribution and gravityof radiological accidents. Consequently, it is not necessarily clear to
the reader that the "deadly" sources are those which emit highenergy radiation (e.g. cobalt-60), whereas most accidents involve
relatively small industrial sources (e.g. iridium-192). Obviously it is
not the role of UNSCEAR to study the lessons which can be derived
from these accidents (the IAEA conducts an in-depth review of eachsevere accident, examining the causes, circumstances and lessons),
but the Committee could have done more than list some accidents
according to a classification based on source utilisation (civil andmilitary uses [there is a marked preference for criticality accidents],
industry, orphan sources, transportation and medicine).

Report R.660 :Exposures from radiation
accidents

3/3

Exposures of the public and workers to various
sources of radiation
This voluminous report serves to update the data in earlier
UNSCEAR reports. The subject matter is one of the body's reasonsfor existing and is thus regularly examined. The report successively
reviews 1/ sources of exposure for the public: natural sources ingeneral, those whose impact is increased by human activity, civil
and military sources; and 2/ sources of exposure for workers:/38

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methods of dose assessment, natural sources, civil and militarysources. The report contains 110 detailed tables (114 pages) and 47
figures (56 pages), which are valuable sources of reference. The
main conclusions are as follows:30•3/ Reports in progress

1/ The estimate of average natural exposure remains unchanged
at around 2.4 mSv per year, mostly due to radon. Doses for all
terrestrial surfaces have a lognormal distribution and in the largest
number of cases, exposure is within the range of 1---10 mSv per year;
2/ Exposure to natural sources of radiation that have been
modified by humans is becoming particularly significant as a resultof newly identified sources whose dose estimates are based on
various scenarios. However, it is not yet possible to provide a global
assessment of these sources, the kind that would allow an
extrapolation for the entire planet;
3/ In this category of sources, mine residues represent enormous
quantities of matter with higher concentrations of naturalradionuclides than normally found in the environment. As a result,these residues are problematic in terms of both storage and siteclean-up. The public exposure associated with these residues is nothigh, but the number of people exposed to low doses can be high ;4/ Civil nuclear reactors have not released large quantities ofradioactive substances; the associated doses are thus low. For theentire nuclear cycle, collective local and regional exposure isestimated at 0.72 man Sv (GW a)-1. Therefore, for a yearly energy
production of 272 GW, the collective dose per production year isapproximately 196 man Sv. For a local and regional population ofaround 250 million, this collective dose corresponds to an average
individual dose of less than 1 μSv per year. If nuclear reactors
maintain their energy production capacity over the next 100 years,
the average individual dose for the global population will have amaximum value of 0.2 μSv, which is small, compared to the dosefrom background radiation;
5/ In terms of man-made radiation sources, atmospheric testingof nuclear weapons accounts for the largest portion of the collective
dose. The resulting exposure is local, regional and global since there
are radioactive deposits over the earth's entire surface. According toestimates, individual doses peaked at 110 μSv in 1963 and havedecreased since then to 5 μSv (mainly due to 14C, 90Sr and 137Cs) ;6/ For populations living near test sites, the level of exposure is
now known and may be high, particularly when these populations
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contamination is considerable, but on the atolls of Moruroa andFangataufa it plays a very moderate role in overall exposure. On the
Marshall Islands and Maralinga, such contamination depends largely
on inhabitants' lifestyles ;31•3/ Reports in progress

7/ When nuclear arsenals were being developed, and particularly
from 1945 to 1960, large populations were exposed to releases
from military installations. It is difficult to accurately assess thedamage because the quality of monitoring was poor and the risks
were hidden ;8/ Enrichment processes generate large quantities of depleted
uranium. The properties of this very dense metal explain its
numerous civil and military uses. Depleted uranium has been usedin recent conflicts. In numerous areas, such as Kosovo, Serbia,
Bosnia and Montenegro as well as Kuwait and Iraq, the public isconstantly exposed to the resulting residues. Several eventualities
have been considered in order to assess the potential consequencesof this exposure. Notwithstanding a few rare scenarios, theestimated levels of exposure are low. The long-term fate of depleted
uranium and whether it will contaminate underground waterremains unknown.
9/ There are still numerous civil sites which once used radioactive
substances and remain contaminated today. Most are contaminatedwith radium and have been identified; many have undergone
decontamination and are generally closed to the public unless they
have been rehabilitated. There are similar problems with residues
from former mine sites. The clean-up programmes aim to bring
exposure levels within acceptable ranges for such ongoing practices.
10/ In general, accidents only affect a limited number of people,
but the doses may be high. Exceptions include the 1983 accident in
Mexico City, the 1987 accident in Goiânia and the 1982---1984
accident in Taiwan. The first resulted in relatively low exposurelevels for the population and was due to the use of 60Co for the
manufacture of concrete reinforcing bars and furniture parts. The
second accident had far more serious consequences; a medical
source of 137Cs was mishandled by several people, resulting inwidespread exposure. Four people were killed and 28 sufferedserious burns. In Taiwan several apartment buildings were built withreinforcing bars contaminated with 60Co. Although the residents
were exposed over several years, the levels of exposure remainedmoderate.

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Medical radiation exposures
This very well-documented report (192 pages including 60 pages oftext, 110 pages of tables and 10 pages of forms and questionnaires)
is much improved compared to the previous document, which
included only a very brief discussion of radiotherapy and nuclear
medicine even though these two fields contribute substantially tothe public's level of medical exposure. The report in question does abetter job of reviewing these fields, but there are still numerous
gaps. For example, doses associated with diagnostic radiology,
including certain recent techniques which are particularly powerful(e.g. computed tomography, interventional radiography,
mammography and bone densitometry) and which often involve
high exposure levels for patients, are far better documented thandoses associated with radiotherapy and nuclear medicine. The
report lists the doses received by patients exposed to during
paediatric and dental radiology procedures, as well as fetal doses.
The dosimetric assessment of these now widely used techniques isof great interest to the healthcare professionals who use them;
most of these professionals are not familiar with all the potential
risks for their patients because in general they are not radiologists
but rather cardiologists, paediatricians, traumatologists, etc.
Techniques involving particularly high radiation doses for patientsare well documented. Certain sections have yet to be written due toa lack of appropriate documentation and references.

Report R.655 :Medical radiation exposures

Previous UNSCEAR reports have shown that of all human activities,
medicine plays the largest role in the global population's exposure
to radiation. Medical radiation involves three different types ofsources: 1/ x-rays used for diagnosis and interventional radiology, 2/various radionuclides used for diagnosis and treatment, and 3/
various types of radiation used mainly for cancer treatment. The useof radiation has increased over time, independently of the quality ofcare in the countries studied. The upward trend is primarily due toincreasingly widespread use of medical equipment that utilises
radiation sources. Moreover, the global trend towards urbanisation
has given more people access to radiological treatment. Medical
radiology is constantly evolving, thanks to continual innovation in
the area of equipment. Techniques allowing outpatient explorationand treatment are popular amongst patients and healthcare
professionals. This continual positive pressure promotes newtechniques such as interventional radiology (used in cardiology andneurology), helical computed tomography and digital imaging.

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Despite the increased number of examinations and techniques
involving radiation, there has been a significant effort to reduce
individual doses. This effort is primarily focused on technicaladvances in equipment, protocol standardisation, measurement ofdoses actually delivered to patients, quality assurance programmes,
etc.

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Diagnostic radiology exposure is continually on the rise; theprimary reason is the increasing number of x-ray exams. There wasan estimated number of examinations of 1.9 billion between 1991
and 1996 (versus 1.6 billion between 1985 and 1990), which isequivalent to a rate of 330 10-3 (versus 300 10-3). And that does notinclude an additional 520 million dental examinations (rate of 9010-3). The collective dose for all diagnostic exams is 2.33 x 106 man
Sv for the period of 1991–1996, which is equivalent to an average
individual dose of 0.4 mSv (1.6 106 between 1985 and 1990, or an
average of 0.3 mSv per person). There is enormous variation in the
global distribution of x-ray examinations due to differing levels of
healthcare in the countries studied: for the period of 1991–1996,
74% were performed in countries with advanced healthcare (rate of920 10-3), 25% in countries with adequate healthcare (50 10-3) andonly 1% in countries with limited healthcare (20 10-3). For the same
period, the average effective dose per exam is 1.2 mSv, comparedwith 1 mSv for the preceding 5-year period. According to the
distribution of exposure levels between the various types of exams,
computed tomography (CT) predominates by a large margin,
especially in countries with advanced healthcare, where it accounts
for 34% of the total dose. CT takes the place of the former "leading"exam, gastrointestinal radiography, which now accounts for only
14% of the total dose. This distribution varies from country tocountry depending on the level of healthcare development: chest
radiography still accounts for 50% of the collective dose inmoderately developed countries and CT accounts for only 2% of
the collective dose in less developed countries. The number of CT
scans has considerably increased in countries with particularly
advanced medical infrastructure. In certain European countries it
has risen by a factor of 6. The use of increasingly sophisticatedequipment, like helical scanners, should have diminished exposure,but this trend has not been able to offset the growing number of
exams.
The use of specialised equipment has led to a decrease in
mammography doses in recent years. Initially doses of 100 mGy per
exam were common; they were first reduced by a factor of 3, then afactor of 10, resulting in doses to the breast of 1---2 mSv.

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UNSCEAR reports
15 september 2006
•IRSN 2006-74

In contrast to exposure resulting from medical diagnostic radiology,
exposure resulting from dental diagnostic radiology has decreased
over time: 14,000 man Sv, or 0.002 mSv per person, for the periodof 1991---1996 (compared to 18,000 man Sv, or 0.003 mSv perperson for the period of 1985---1990). Medical examination doses
cannot be translated directly into potential risks, because theindividuals who receive these doses are for the most part elderly
and/or sick and thus not representative of the entire population. The
reverse is true for dentistry: patients are increasingly young.

34•3/ Reports in progress

The exposure data for children and fetuses are particularlyinteresting. The studies of children come from paediatricdepartments in Belgium, the United Kingdom and Spain. The
Belgian study shows that computed tomography delivers individual
doses (effective dose) of 0.4---2.3 mSv to the skull, 1.1---6.6 mSv tothe thorax and 2.3---19.9 mSv to the abdomen. The treatment ofvaricocele in adolescents delivers an effective dose of 18 mSv. The
studies performed on fetuses come from Iran, the United Kingdom,
the United States and Germany. For 1,300 pregnant Iranian patients
who underwent CT scans for mild gastrointestinal or urinary
problems, the dose to the fetus (4 weeks old on average) was 6---8
mGy. Most English women examined presented more than 8 weeks
into their pregnancies; 85% of the fetuses were exposed to a dose
below 5 mGy (only five fetuses received more than 10 mGy). The
American study on exams involving helical CT (detection of
pulmonary embolism in the mother) shows fetal doses of 3.3---20.2
μGy for the first trimester and of 51.3---130.8 μGy for the third
trimester. These doses are high, but they are still lower than dosesdelivered by scintigraphy under the same circumstances.
The number of deterministic effects in patients treated withinterventional radiology is markedly underestimated; these effects
are not reported on a regular basis because patients often receive
insufficient follow-up from their physicians, who are not always
aware of the possible complications of radiotherapies.
Bone densitometry is used in children to monitor bone growth andin older people to assess the risk of fracture, especially inmenopausal women. The report provides effective doses which on
average range from a few mSv to a few tens of mSv, depending on
the type of exam. Unfortunately, the report does not provide doses
absorbed by bone, which would be more interesting if only for the
purposes of comparison.
There is a clear commitment on the part of the authorities,
equipment designers and healthcare professionals to reduce the© IRSN/2006 --- All right reserved/38

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•IRSN 2006-74

levels of patient exposure. Personnel education and training canreduce doses up to 40%. The ICRP Publication 73(1996) and the(1997) provide reference
European Directive 97/43/EURATOM
levels for diagnosis, including optimal levels for each type of exam.
Moreover a number of techniques allow considerable dose
reduction. By limiting the number of redundant films, doses can be
reduced up to 40%; by using pulsed fluoroscopy for angiographies
and in a large proportion digital imaging and other procedures,
doses can be reduced by 32% to 66%. As for the UNSCEAR report,
it complements the recent ICRP reports
concerning
radiology practices involving particularly high doses for patients andhealthcare professionals.
Nuclear medicine regularly uses various radioactive substances fordiagnostic or treatment purposes, primarily 99mTc, 123I, 125I, and 131I.
The report provides data on the size of patient populations affectedby diagnostic procedures: throughout the world there were 32.5
million examinations per year between 1991 and 1996, which isequivalent to a rate of 5.6 10-3 (24 million for the period of 1985–
1990, or a rate of 4.5 10-3); this figure is small compared to thediagnostic radiology figure. The majority of these examinations andtreatments (89%) took place in more developed countries. A small
number (11%) took place in moderately developed countries and avery small number (less than 1%) took place in less developed
countries. The corresponding collective effective dose – 150,000
man Sv or 0.03 mSv per person for the period of 1991 to 1996 – isunchanged compared to the preceding period, indicating decreased
exposure levels for each type of exam given that the number of
exams has risen. There are 400,000 treatments per year involving
radionuclides, which is equivalent to a rate of 0.065 10-3. The same
figure applies to brachytherapy.
Radiotherapy is used primarily for patients with cancer. This typeof treatment is often used in association with surgery and/or
chemotherapy. The proportion of patients treated by radiation mayvary considerably from one country to the next. There are twotreatment techniques: teletherapy, which uses an external beam ofradiation directed at the target area, and brachytherapy, which uses
a radioactive source placed directly in a natural cavity or organ.
Unsealed source radiotherapy and monoclonal antibodies are also
used to treat metastases. There are four families of teletherapy
radiation: 1/ 60Co gamma radiation, 2/ 137Cs radiation (but 50–300
kVp x-rays are increasingly used as an alternative), 3/ electrons andx-rays produced by linear accelerators, and 4/ protons and charged
particles from cyclotrons and synchrotrons. Particle accelerators are

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International Commission on
Radiological Protection. ICRP
Publication 73: RadiologicalProtection and Safety in
Medicine. Annals of the ICRP,
Vol. 26(2). Pergamon Press, 1996

European Union. Council
Directive 97/43/EURATOM on
Health protection of individuals
against the dangers of ionizing
radiation in relation to medical
exposure, and repeating Directive
84/486/EURATOM, 1997

International Commission on
Radiological protection.
Radiation dose to patients fromradiopharmaceuticals. ICRP
Publication 80, Pergamon Press,
Vol. 28, N° 3, 1998

International Commission on
Radiological protection. Pregnacyand medical radiation. ICRP
Publication 84, Pergamon Press,
Vol. 30, N° 1, 2000

International Commission on
Radiological protection.
Avoidance of radiation injuries
from medical interventional
procedures. ICRP Publication 85,
Pergamon Press, Vol. 30, N° 2,
2000

International Commission on
Radiological protection.
Prevention of accidental
exposures to patients undergoingradiation therapy. ICRP
Publication 86, Pergamon Press,
Vol. 30, N° 3, 2000

International Commission on
Radiological protection.
Managing patient dose in digitalradiology. ICRP Publication 93,
Pergamon Press, Vol. 34, N° 1,
2004© IRSN/2006 --- All right reserveddoc reference
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UNSCEAR reports
15 september 2006
•IRSN 2006-74

still rare and are concentrated in Europe, the United States andJapan. The total number of external or internal radiotherapy
treatments provided throughout the world between 1991 and 1996
is estimated at 5.1 million (90% involved teletherapy), which isequivalent to a rate of 0.9 10-3. The same figure applies to theperiod of 1985–1990. As for diagnostic radiology, there are major
variations depending on the level of healthcare development: 51%of treatments occurred in more developed countries (rate of 1.7
10 -3), 43% in moderately developed countries (rate of 0.7 10-3),
6% in less developed countries (rate of 0.5 10-3) and 1% in thepoorest countries (rate of 0.07 10-3).

36•3/ Reports in progress

Intravascular radiotherapy, which is technically comparable tointerventional radiology, involves introducing a sealed source in thelumen of a stenotic blood vessel. The report offers little discussionof this localised technique, which is used to treat many vasculardiseases, but it does provide a table of doses including most of thecommonly used procedures. Local doses are rarely less than a few
tens of mGy and often above a few hundred mGy, even reaching a
few Gy in some cases.
The report also shows that the number of machines varies greatly
from one country to the next, depending on the level ofdevelopment. For example, the linear accelerator capacity (number
per million inhabitants) is 3.04 in more developed countries, 0.26 inmoderately developed countries, 0.06 in less developed countries
and nonexistent in the least developed countries. The range ofvariability is broad: there are no linear accelerators in either
Lithuania or Ecuador whereas the United States has 7.28 per million
inhabitants. The number of patients treated is directly proportional
to the number of machines available. Likewise, the frequency of
teletherapy treatment is 30 times higher in the best-equippedcountries than in the poorest countries. In a sample of 28 moredeveloped countries, treatment frequency is between 0.7 10-3 and37 10-3; in a sample of 19 moderately developed countries, therange is from 0.05 10-3 to 3.1 10-3; finally, in a sample of 6 lessdeveloped countries, the range is from 0.05 10-3 to 2.1 10-3.
In conclusion, this report is incomplete in several areas. The
questionnaires supplied at the end should allow many of the gaps tobe filled in the areas of nuclear medicine and biomedical research,
and also with regard to many developing countries. Obviously
radiological protection is not the subject of this report, but it isunfortunate that it does not assess exposure among healthcare
professionals, which is becoming problematic for certain newer© IRSN/2006 --- All right reserved/38

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methods of investigation. Another shortcoming is the lack of
information about the dosimetric impact of systematic screening
using diagnostic radiology.

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15 september 2006
•IRSN 2006-74

38• 4/ Conclusion

4/

Conclusion
The UNSCEAR reports summarised in the present document can bedivided into two groups: 1/ technical reports, which are part of
UNSCEAR's primary mission and closely tied to its reasons forexisting, i.e. identification of all radiation sources and quantificationof public and professional exposure, detailed analysis of exposuredue to radon, assessment of medical exposure and evaluation of theeffects of radiation on humans as well as plants and animals; and 2/
scientific reports, which are upstream of the technical reports andexplore the aetiological and physiopathological aspects of thevarious effects of radiation, i.e. mechanisms and epidemiology ofradiation-induced carcinogenesis, mechanisms of noncancer effects,
immune system reactions to radiation, and non-targeted anddelayed effects.

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