Answer to Question #12046 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment and Shielding — Equipment

The following question was answered by an expert in the appropriate field:

Q

We were asked by our local authority to purchase a dose calibrator to verify iodine-131 (131I) activity before giving the radionuclide to patients. We are a small hospital that provides only iodine treatment with no other radionuclides used. Since the cost of a dose calibrator is very expensive in our country, I have measured the dose rate of the 131I capsule kept inside a lead pot (purchased from GE, United Kingdom) using a survey meter from a specific distance. Then I compared the measured dose rate with the dose rate calculated using RadPro Calculator. I have found that my results are always within 5% of the expected activity. My questions are: (1) Is this method acceptable, and is it used in any other country? (2) Are there any research papers that can justify my method (I have tried Google, but found none)?

A

The answer to your first question is yes, your dosage determination methodology is a sound one. The answer to your second question is one that unfortunately I do not know, and I was unable to find a research paper that justifies your methodology.

Since it appears you are verifying the dosage determined by another licensed preparer (e.g., nuclear pharmacy) and your method uses the same principles as a dose calibrator, I feel these two considerations should be adequate justification. I do not know what your local authority feels about US regulatory requirements, but you may want to let your local authority know that in the United States if a "unit" dosage (i.e., a dosage that is not altered after being dispensed) is administered to a patient, the hospital is not required to make a second measurement and may determine the dosage administered by applying a decay correction to the activity or activity concentration determined by the manufacturer or preparer licensed (e.g., nuclear pharmacy).

In regard to obtaining a dose calibrator, I am not sure obtaining one would provide better dosage information than the method you are using. Also, you should be aware that in addition to purchasing the dose calibrator, you will also need to obtain standards and routinely perform the quality control tests applicable to assuring the dose calibrator is functioning properly. Standard practice is for a geometry test to be performed at installation, an accuracy test to be performed annually, a linearity test to be performed quarterly, and a constancy test to be performed each day of use. Each of the tests must also be performed if the dose calibrator is moved or repaired.

Victoria (Vicki) Morris, MS, CHP

Reference

US Nuclear Regulatory Commission. Determination of dosages of unsealed byproduct material for medical use. Washington, DC: US Government Printing Office; 10 CFR 35.63(b)(1); 2007. Available at: www.nrc.gov/reading-rm/doc-collections/cfr/part035/part035-0063.html. Accessed 5 July 2017.

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Answer posted on 6 July 2017. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.