http://www.arpansa.gov.au/pubs/rhs/rhs26.pdf
POLICY ON STABLE
Iodine PROPHYLAXIS FOLLOWING NUCLEAT REACTORS ACCIDENTS (1989)
Approved at the 107th session of the
National Health and Medical Research Council,
Sydney, June 1989.
Published by the Australian Radiation Laboratory
on behalf of the
National Health and Medical Research Council (September 1989)
© Commonwealth of Australia 1989
The objective of the National Health and Medical Research Council is to advise the Australian community on the achievement and maintenance of the highest practicable
standards of individual and public health and to foster research in the interests of improving those standards.
CONTENTS
1 Introduction 1
2 Scope of policy 1
3 Justification of stable
Iodine prophylaxis 1
4 Action levels 2
5 Stable
Iodine prophylactic doses 2
6 Contraindications 3
Appendix 4
Adverse reactions to iodine 4
General notes 4
1 INTRODUCTION
In any accident that releases radioiodines to the environment, one countermeasure
that may need to be considered to reduce the effect of inhalation of radioiodines by
persons downwind of the point of release is to provide those persons with tablets
containing stable iodine. Radioiodines would normally be assimilated in the thyroid
gland, but the provision of tablets containing stable iodine ‘blocks’ that gland,
reducing the uptake of radioiodines and thus reducing the ionizing radiation dose to
the thyroid.
Both potassium
Iodide (KI) and potassium iodate (KI03) are effective prophylactics
but UK experience has shown that the tablets composed of KI03 may be stored for
longer periods without deterioration. Australian-made
KI tablets have not suffered
from a similar storage defect, presumably because a different manufacturing method
has been used. Nevertheless KI03 has become the usual chemical form of
prophylactic tablets for this purpose in Australia.
2 SCOPE OF POLICY
This policy considers the alleviation of possible hazards that may arise from any
radioiodines inhaled from a plume of fission products emanating from a nuclear
reactor accident. Such a nuclear reactor may be land or ship-based.
There are two predominant exposure scenarios, which depend on the distance of
the person from the source of radioiodines. The ‘near field’ situation is the one
where the main route of exposure to radioiodines is via inhalation, while the ‘far
field’ situation is where the main route of exposure would be by ingestion of
contaminated food. In the Australian context, the far field scenario is not
considered a significant source of exposure and hence it is not considered further in
this document.
The policy does not consider the long-term hazards resulting from radioiodine
uptake by the thyroid (e.g. production of thyroid nodules or thyroid cancer), nor the
internal dose commitment from other radioisotopes that may be released to the
atmosphere during a reactor accident.
3 JUSTIFICATION OF STABLE IODINE PROPHYLAXIS
The only countermeasure that provides effective prophylaxis against the effects of
radioiodines on the thyroid gland is oral stable iodine therapy. If 100 mg of iodine in
the form of
KI or KI03 is taken at the time of exposure, thyroid doses from
radioiodines are reduced, on average, to around 1-2 percent of those that would
otherwise have been the case. There will, however, be individual variations in
effectiveness, and in some cases, the thyroid dose, may be as high as 10 percent of
that which would have been the case without the use of stable iodine.
Administration of stable iodine does not reduce the hazard to the thyroid from
external radiation. The magnitude of the external radiation hazard from a plume of
fission products following a reactor accident will depend upon the types and
amounts of fission products released (that is, the ‘source term’).
Stable iodine will not provide protection against any radioisotopes other than
radioiodines and will not protect body organs other than the thyroid.
Other countermeasures such as sheltering, evacuation, respiratory protection, etc.
may need to be considered in the overall response action to such an accident.
Stable iodine is an inherently safe medication with an incidence of side-effects of
around 10-6 to 10-7. On the other hand the risk of fatal thyroid carcinoma for a
thyroid dose of around 500 mSv (which is in the upper range of the action level) is
10-4 clearly showing that the small risk associated with stable iodine prophylaxis is
justified compared with the higher risk associated with the radiation exposure that
may follow if it is not used.
4 ACTION LEVELS
For a possible thyroid radiation dose of 50 mSv, stable iodine prophylaxis should be
considered and for a thyroid radiation dose in excess of 500 mSv it is regarded as
essential.
5 STABLE IODINE PROPHPYLATIC DOSES
This advice is based on the use of tablets of 170 mg potassium iodine, or 130 mg
potassium iodide, containing 100 mg stable iodine.
The recommended doses are -
(a) Adults (including pregnant women and lactating mothers) - single dose of one
tablet.
(b) Infants, children and adolescents (one month to 16 years) - single dose of half
a tablet.
(c) Neonates (birth to one month) - single dose of one quarter of a tablet.
(d) Emergency personnel - one tablet per day for up to ten days.
Where possible, the tablet should be taken before, but in any case as soon as
possible after, exposure to the plume. The efficacy, that is, dose reduction achieved, of thyroid blocking falls to about 50 percent and 5 percent if the stable iodine prophylactic dose is delayed 6 and 12 hours respectively.
Where continued exposure is considered likely it is assumed that the source will be
removed or that sheltering or evacuation of the affected population will take place.
Only emergency personnel might therefore require repeated doses of stable iodine.
Repeated doses should not be given to pregnant women, lactating mothers and
neonates.
6 CONTRAINDICATIONS
A history of allergy to iodine is a relative contraindication. Personnel with iodine
allergy, or any of the conditions listed in the Appendix, should not be employed in
reactor accident response teams. Such personnel should be evacuated from potential
risk areas and, if possible, provided with suitable respiratory protection.
For members of the general public, it is not practical to anticipate possible
contraindications unless it is known that certain individuals have a personal aversion to iodine. In general, due to the low incidence of contraindication, one stable iodine tablet can be given with confidence in view of the benefit of reduced probability of radiation effect.