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Estimation of Radiation Dosage and Transmutation Effect of ¹⁴C Involved in Measuring Rate of Albumin Synthesis with ¹⁴C-Carbonate

St. Radboud Hospital, University of Nijmegen, Nijmegen, The Netherlands

Correspondence: For reprints contact: S. H. Yap, Div. of Gastroenterology and Nuclear Medicine, Dept. of Medicine, St. Radboud Hospital, University of Nijmegen, Nijmegen, The Netherlands.

ABSTRACT

For direct measurement of the rate of albumin synthesis Na₂¹⁴CO₃ was used intravenously. The assessment of the radiation hazard involved in the study was based on the knowledge of the minimum dose of Na₂¹⁴CO₂ necessary for a sufficient incorporation of ¹⁴C in the guanidine-C of arginine in albumin to obtain measurable radioactivity. By measurement of expired ¹⁴CO₂ and excreted ¹⁴C-urea in the urine during a 5-hr period following intravenous administration of Na₂¹⁴CO₃ in five subjects, some quantitative data on ¹⁴C retention and radiation dosage were obtained. In comparison with animal studies, the rate of expiration of ¹⁴CO₂ in man is slower. About 50% of the total radioactivity injected was lost through the respiratory route in the first hour. The total amount of expired ¹⁴C during the 5 hr of investigation was about 75% of the injected dose for the five subjects. The amount of ¹⁴C excreted as urinary ¹⁴C-urea during the 5 hr of investigation is very small in comparison with the expired ¹⁴C; it was only about 0.5% of the dose injected. The total absorbed radiation dose after complete elimination of ¹⁴C from the body was calculated with various assumptions. The extra risk of genetic damage due to disintegration of retained ¹⁴C in comparison with that of natural ¹⁴C in the body during 30 living years is about 50%.