OFFICIAL L2= ONLY
Radiciodine appearing in urine, except for that during a relatively
short period following exposure, originates from the thyroid. In the calculation for urinary radioiodine it was aseumed that iodine is released from the
: thyroid only as thyroxine, and that the release of thyroxine and its aubsequent degradation in the extrathyroidal hormonal space can be adequately
described assumingfirst-order kinetics. Ranges for normal biological
half-life of iodine in the thyroid and normal turnover rate of extrathyroidal
thyroxine were selected from the best available data in the literature, The
uptake of radioiodine was asaumed to be exponential with a half-period of
increase of 4.5 hours, and 60% of the iodine released when extrathyroidal
thyroxine is degraded was assumed to be excreted in urine.
Rateg of urinary radioiodine excretion were calculated from the regult-
3.7
3.7
3.7
3.7
K
day”! x 109
4.85
4.85
17.15
17,15
Rh * 0-60 LKT
eK tA. (Ltn
L-K
The problem outlined above is a practical application of an analytical
study on the uptake and excretion of iodine in man which will be described
more fully in a UCRL report entitled, "The Dynamics of Iodine in Man."
eT tK tantran
L-jJ-k
Iry * peak radioiodine content of the thyroid
maaan
iOuax }
Xx = physical decay constant for 31
J = rate constant for the uptake of radioiodine in the thyroid
vo.
|
On the basis of these calculations, the normal range of urinary radio-
L = rate of turnover of extrathyroidal thyroxine
K * rate constant for the release of iodine from the thyroid
t = time.
A sum:naryof the calculations made to determine the normal range
of urinary radioiodine excretion at 15 days appears below.
OFFICIAL USE ONLY
~)
0.050
0.086
0.16
0.21
iodine excretion at 15 days was estimated to be 0.05 to 0.2% of the peak
thyroid content.
Iu" radioiodine content of urine
oal
Y
% of 1 jay
7.2
13.8
7.2
13.8
where
ya
ar,
L.
day! x10?
ing expression shown below.
diy
aia
J
day”!
see tS
mm tenn a ee |
LOuax
CALCULATION OF URINARY RADIOIODINE EXCRETION
Yook C, Ng
woes TOEaTCRPEg Fe
Urinary radiolodine excretion at 15 days.
APPENDIX
IEONRNR rs Bere =
-T-