Information Notice No. 90-59: Errors in the Use of Radioactive Iodine-131

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                             September 17, 1990

Information Notice No. 90-59:  ERRORS IN THE USE OF RADIOACTIVE 


All medical licensees. 


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 

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.


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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                                                         Page 3 of 4 

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 

1. List of Recently Issued NMSS
   Information Notices.
2. List of Recently Issued NRC 
   Information Notices. 


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