Correlation between external exposure and activity in patients undergoing 131I thyroid cancer therapy.

The uptake and clearance of 131I activity for inpatients undergoing cancer therapy were determined from routine external dose survey measurements. A bi-exponential behavior was found, with the two time constants representing the iodine dynamics in the thyroid on one hand and in the rest of the body on the other. The external dose at 1 m from the patient was correlated to the activity in the thyroid remnant and inside the body, the averaged value being 52.8 +/- 11.4 microSv GBq(-1) h(-1). The temporal evolution of activity in the body, the urinary system and the thyroid remnant area were determined taking into account the clearance from thyroid and whole body (effective retention constants averages 0.23 +/- 0.14 d(-1) and 1.46 +/- 0.34 d(-1)) and the uptake in thyroid (3.15 +/- 3.36%). Applications of this study in the public and environmental radiation protection areas are presented.