RT Journal Article
SR Electronic
T1 Improved Prediction of Therapeutic Absorbed Doses of Radioiodine in the Treatment of Thyroid Carcinoma
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 1084
OP 1090
VO 42
IS 7
A1 Jindřiška Heřmanská
A1 Miroslav Kárný
A1 Jaroslav Zimák
A1 Ladislav Jirsa
A1 Martin Šámal
A1 Petr Vlček
YR 2001
UL http://jnm.snmjournals.org/content/42/7/1084.abstract
AB We proposed an alternative to a monoexponential model of radioiodine kinetics to obtain a more accurate estimate of absorbed doses to postsurgical thyroid remnants. We suggested that part of the difference between the predicted and the actually absorbed therapeutic doses of 131I, usually explained by radiation damage of thyroid cells, can be attributed to errors resulting from inadequate sampling of data and oversimplified modeling. Methods: A standard monoexponential model and alternative biphasic model (incorporating both radioiodine uptake and clearance) were used on 2 sets of patient data to fit time–activity measurements after administration of diagnostic and therapeutic activities of radioiodine. One set of data consisted of 633 records of routine measurements, and the second set consisted of 71 prospectively collected records with measurements performed more frequently and for a longer time. The time–activity curves derived from the 2 models were used to calculate residence times for diagnostic and therapeutic activities of 131I, and the respective residence times were compared using the paired t test. Errors of fitting and prediction of therapeutic time–activity data were also calculated. Results: With both models, a statistically significant difference (P < 0.01) was found between residence times after diagnostic administration of 131I and residence times after therapeutic administration of 131I. However, the effects of biphasic modeling and of improved sampling substantially reduced the difference (P < 0.01). Errors of fitting and prediction were smaller with the biphasic model than with the monoexponential model (P < 0.01). Conclusion: The biphasic model more accurately predicts 131I kinetics when applied to measurements in the short interval after diagnostic administration of radioiodine. The minimum requirement for the biphasic model is measurement twice a day at intervals > 6 h for at least 3 d after administration.