Answer to Question #5485 Submitted to "Ask the Experts"

Q

Yesterday I had a thallium stress test to investigate the causes of chest pain. I have an 11-month-old baby and was told by the radiologist to have reduced contact with him for 24 hours in view of the fact that I was injected with thallium. My cardiologist recommended reduced contact with him for two to three days as the thallium has a half-life of 72 hours. I have had reduced/little contact with him for 24 hours but am now concerned that I should not have contact with him for an additional two days. What do you recommend?

A

The issue of exposure to family members and the public from patients who have received radionuclides for medical tests and treatment has been considered by the U.S. Nuclear Regulatory Commission (NRC). Essentially, exposures to individuals who are not the patient are to be kept below 500 mrem, whereas our exposure from background radiation for all sources is approximately 360 mrem per year. Evaluation and recommendations to keep exposure below 500 mrem are summarized in Appendix U of NUREG-1556, Vol. 9, Rev. 1, "Consolidated Guidance About Materials Licenses: Program-Specific Guidance About Medical Use Licenses."

If the exposures from a released patient were to result in the exposures to the public or family members above 500 mrem, special instructions would be given to the patient. As noted in Table U-2 of this appendix, if you were given a dose of 85 mCi of ²⁰¹Tl for medical studies, your physician would have had to give you special written instructions that would have reduced any risk to your child. However, the typical dose of ²⁰¹Tl for a heart scan is about 2-3 mCi, which is significantly below the 85 mCi dose where precautions are necessary to reduce exposures to your child. Consequently, I would not worry about reduced contact with your child beyond the first day.

I would caution you that there are some minor radioactive components in a dose of ²⁰¹Tl that have half-lives longer than 72 hours. See our Ask the Experts Q 4779 under the Topical Area "Medical and Dental Patient Issues." While these radiations do not contribute to any significant doses to individuals, they are readily detected by sensitive radiation-detection equipment such as that used at airports. Periodically, there are stories in the news of individuals, such as you, who have triggered such alarms.

John P. Jacobus, MS
Certified Health Physicist