Answer to Question #9091 Submitted to "Ask the Experts"

Category: Nuclear Medicine Patient Issues — Therapeutic Nuclear Medicine

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


I want to know the amount in percentage of sweating excretion (perspiration) of an administered 131I dose (for example: 3700 MBq). We know the fecal excretion is about 10 percent, renal is about 70 percent, but I haven't found the percentage in perspiration and salivary fluid.


First of all there is a difference between the 131I kinetics for treatment of hyperthyroidism and thyroid cancer. Since you have mentioned 3700 MBq, I assume you are looking for the pertinent values after oral sodium 131I treatment for thyroid cancer. If this is the case, the percentages you cite for urinary and fecal excretion appear to be incorrect; 70 percent is too low and 10 percent is too high. Unfortunately, you will be hard pressed to find percentages for excretion via perspiration and saliva, rather than measured values at various times post-administration. I refer you to the following two publications for measured levels of 131I from thyroid cancer and hyperthyroid patients:

  1. Ibis E et al. Iodine-131 contamination from thyroid cancer patients. J Nucl Med 1992; 33:2110-2115; and
  2. O'Doherty MJ et al. Radiation dose rates from adult patients receiving 131I therapy for thyrotoxicosis. Nucl Med Commun 1993; 14:160-168.

For example, according to the Ibis article, the amount of 131I excreted via perspiration is maximal at about 24 hours postadministration and measured activities at this time have varied from 11.1 to 248 Bq, depending on the body part sampled (forehead, chest, neck, hand). As values at 4, 24, and 48 hours are given you could add them all up at each sampling time, make some assumptions about the remaining non-sampled areas of the body, and then integrate this activity-time curve to very roughly estimate the total percentage of 131I excreted via perspiration.

Given that only Bq quantities have been measured, only a very small percentage of the administered activity will most likely be found to be associated with excretion through perspiration. Salivary activity has been similarly determined; however, this latter estimation method for salivary excretion cannot be used since the saliva is nearly completely swallowed by the patient and the 131I is reabsorbed into the blood.

Jeffry A. Siegel, PhD

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 11 June 2010. 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.