PRIVACY ACT MATER l AL O”A REMOVED COUN, ROSOFF, GUSMANO AND SPENCER 656 TABLE I DeSCRIPTION OF PATIENTS ae Patient - ~- Dase af . . ae Route af ud ministration Age (years) Sex . . Diagnosis 50 25 Oral Oral 57 73 M M FPulmonary tuberculosis, inactive MHypopituitarism secondaryto pitui- 10 10 10 Intravenous Intravenous Oral 45 70 60 F M F Carcinoma of colon Malignant lymphoma Malignant lymphoma tary tumor adininistration are presented in Table I. All subjects were outpatients and were counted on the average of three times a month. The variation in the counting rate for the photopeak of a point souree of Cs!3* is £0.24, The precision of the counter for Cs'*7 in man is 0.36 ingc. The per cent standard deviation of the count rate in a patient for a 10-mimute count one year after the oral administration of 50 we of Cs!8" is £0.27. The variability of the 10- minute background over a 30-day period is 1.10%. The variation in the count rate due to reproducing the patient’s position on the cot is less than 2%. The Brookhaven-Merlin computer was programmed to determine the best least-squares fit for the curves and the standard errors, RESULTS AND DISCUSSION The whole-body retention data for intravenously-administered Cs'* for a representative patient ( _ are shownin Fig. 1. The biological retention of Cs'3* for all patients can be described by a sum of a number of exponential functions. However, only the final exponential component is considered in this report, as it represents 85 to 95% of the administered dose and thus accounts for practicallyall Ths ETOe OPER eRe Sr, epeeemege— ie it Mere nL acai,Ei siti, = . 3042747 bceRelCae asa tA PRIVACY ACT MATERIAL REMOVED al ies the radiation dose in all patients studied. The intercepts (4) und rate constants (A) of this major exponential component for each patient, along with their standard errors, as determined by computer analysis, are presented in Table IT. In order to chiminate the effect on the geometry, andthus on the counting, of the initial variations in distribution of the administered isotope, Cs!’ retention values were Obtained from the excretion data for the first few weeks of the study. Thus, the curves were nornuuized to the retention values obtained by analysis of excretion in patients ‘ and over the first 3 weeks. The values for the biological half-life reported here range from 54 to 114 days, with a mean of 75 days. This value is in agreement with that obtained by Lidén (2), who reported «a biological half-life of 74 days in one male injected intravenously, A similar spread in the values for biological half-life in a situation of 4 4