Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIALS SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
September 17, 1990
Information Notice No. 90-59: ERRORS IN THE USE OF RADIOACTIVE
IODINE-131
Addressees:
All medical licensees.
Purpose:
This information notice is intended to emphasize to medical use licensees
the potential radiation dose levels resulting from errors in the
administration of iodine-131 to humans. This issue was previously addressed
in Information Notice No. 85-61, Suppliment 1: Misadministrations To
Patients Undergoing Thyroid Scans (attached). Due to the significance and
frequency of recurrence of these errors, NRC believes this issue should be
readdressed. It is expected that licensees will review this information for
application to their own procedures for the administration of iodine-131,
distribute the notice to those responsible for radiation safety and quality
assurance, and consider actions, if appropriate, to establish procedures to
preclude the misadministration of iodine-131 at their facilities. However,
suggestions contained in this notice do not constitute any new U.S. Nuclear
Regulatory Commission (NRC) requirements, and no written response is
required.
Description of Circumstances:
The following cases are recent events reported to NRC that have resulted in
unintended radiation doses to humans, as a result of the administration of
radioactive iodine:
Case 1: A patient with a history of thyroid cancer was scheduled for her
yearly whole-body scan. Before the scan, the patient underwent a pregnancy
test, with negative results. After the pregnancy test results were
received, the technologist began to complete a departmental questionnaire to
obtain information from the patient relative to the requested procedure.
The questionnaire addressed the possibilities of pregnancy and lactation.
However, before completing the questionnaire, the technologist was called
away and did not return to complete the form before administration of the
iodine-131. As a result, the patient was given the intended dosage of 4.89
millicuries of iodine-131. Approximately 48 hours later when the patient
was scanned, there was considerable iodine-131 uptake in her breasts. When
questioned by the physician, the patient indicated that she had given birth
to a female infant two weeks earlier and had been nursing this infant for
approximately the last 36 hours. The total body dose to the infant was
estimated to be 17 rads, and the radiation dose to the infant's thyroid was
estimated to be 30,000 rads. A synthetic thyroid hormone replacement has
been prescribed for the child, with scheduled periodic follow-ups. The
unintended dose to the mother's breasts was estimated to be 8.9 rads.
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Case 2: A patient to be scheduled for a thyroid scan was administered 3
millicuries of iodine-131 instead of the intended dosage of 300 microcuries
of iodine-123. The patient's physician called in the request for a thyroid
scan to the secretary of the nuclear medicine department, who inadvertently
scheduled a whole-body scan. No written request from the physician was
required. The dosage at this facility for a whole-body scan is 3
millicuries of iodine-131, whereas the dosage for a thyroid scan is 300
microcuries of iodine-123. The estimated dose to the patient's thyroid
gland due to this error was 4700 rads.
Case 3: A patient was scheduled for an ectopic thyroid evaluation, with an
intended dosage of 100 microcuries of iodine-131. In completing the Nuclear
Medicine department referral sheet, the referring physician incorrectly
requested a post-thyroidectomy neck scan. As a result, the patient was
administered 1 millicurie of iodine-131, with an estimated dose to the
thyroid of 1300 rads.
Case 4: A patient was scheduled for an ectopic thyroid evaluation, with an
intended dosage of 50 to 100 microcuries of iodine-131. The technologist
consulted the department procedure manual that listed prescribed dosages for
specific scans, and the dosage was incorrectly listed as 4.5 millicuries.
As a result, the patient was administered 4.3 millicuries. The estimated
dose to this patient's thyroid gland was 4300 rads.
Case 5: A patient was administered a dosage of 15 microcuries of
iodine-131. Almost immediately following the administration, the patient
indicated to the technologist that she was approximately 4 to 5 weeks
pregnant. The technologist failed to ask the patient if she was pregnant
before the administration. The patient had arrived at the department with a
baby in her arms, and the technologist assumed that the patient was not
pregnant. The total body dose to the fetus was estimated to be 2 to 4
millirem. Since the fetal thyroid is incapable of concentrating iodine-131
until approximately 12 weeks of gestation, it was estimated that there was
no additional dose to the fetal thyroid.
DISCUSSION:
All licensees are reminded of the importance of ensuring the safe
performance of licensed activities, in accordance with NRC regulations,
requirements of their licenses, and accepted medical practice. The
forementioned cases illustrate: the lack of familiarity with appropriate
thyroid studies and dosages; the necessity of consistently following quality
control procedures; and a need to understand the significance of radiation
doses that result from the administration of millicuries versus microcuries
of radiopharmaceuticals containing radioiodine. Specifically, the radiation
dose to the thyroid, resulting from a dosage of one millicurie rather than
one microcurie of
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iodine-131, is a one thousand-fold increase. In addition, the radiation
dose received from an activity of iodine-131 is approximately 100 fold
greater than the dose from the same activity of iodine-123. The following
table illustrates the relationship between microcurie versus millicurie
quantities of iodine-131, as well as the radiation dose differential between
iodine-123 and iodine-131, for three different age groups, with a thyroid
uptake of 15 percent.
TABLE: A Comparison of Isotopes and Radiation Doses for
Various Age Groups Assuming 15% Uptake by the Thyroid*
Rads per uCi Rads per mCi
I-123 I-131 I-123 I-131
1 year old 0.07 7.40 70.3 7400
5 years old 0.04 4.07 40.0 4070
Adult 0.007 0.78 7.0 777
* Based on information from ICRP Publication No. 53
All workers should have a clear understanding of the significance of errors
in scale when calculating and preparing diagnostic dosages versus
therapeutic dosages of radiopharmaceuticals containing radioiodine. The
threshold at which a diagnostic dosage becomes a therapeutic dosage is low,
and depends on the age of the patient and the percent uptake by the
patient's thyroid gland. Consequently, the potential for causing a
significant, undesired radiation dose to a patient's thyroid gland must
always be kept in mind when administering iodine radiopharmaceuticals.
Licensees are reminded that the package inserts provided by the
manufacturers contain information pertinent to both proper dosages and
radiation doses, and may be valuable resources when reviewing imaging
policies and procedures for errors and inconsistencies. Nuclear medicine
department procedures should include provisions for questioning female
patients about the possibility of pregnancy or lactation. By attention to
detail, and adherence to departmental policy and procedures, many incidents
involving radioactive iodine-131 may be avoided.
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No specific written response is required by this information notice. If you
have any questions regarding this matter, please contact the appropriate
regional office or this office.
Richard Cunningham, Director
Division of Industrial and
Medical Nuclear Safety
Office of Nuclear Material Safety
and Safeguards
Technical Contact: Sally Merchant, NMSS
(301) 492-0637
Attachments:
1. List of Recently Issued NMSS
Information Notices.
2. List of Recently Issued NRC
Information Notices.
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