Calculation of the total number of radiation decay of Radiolabelled-Octreotate using non-linear mixed effect models

Abstract

Non-Linear Mixed Effect (NLME) is a method used in the area under the measured time-activity curve (AUC) calculations. The calculation of an accurate AUC is needed for an accurate determination of the radiation absorbed dose. In NLME, the error model might affect the accuracy of the estimation of the AUC. Therefore, the aim of this study was to determine the effect of error models on AUC calculations using NMLE. The data used in this study were from biokinetic data of the 111In-DOTATATE biodistribution in the tumour collected from the literature. The data were fitted using published bi-exponential function $f(t) = {{({{\rm{k}}_e} \times {{\rm{k}}_a})} \over {c({{\rm{k}}_a} - {{\rm{k}}_e})}}\left[ {{e^{ - ({{\rm{k}}_e})t}} - {e^{ - ({{\rm{k}}_a})t}}} \right]$ with several error models, namely constant, proportional, combined and exponential errors. The mean and standard deviation were determined from the AUC for each error model AUC values obtained from constant, proportional, combined, and exponential error were (4.40 ± 1.93) nmol·min, (3.13 ± 2.74) nmol·min, (3.22 ± 2.85) nmol·min and (3.14 ± 2.75) nmol·min, respectively. Based on the research results, the proportional, combined and exponential error were relatively produced better results compared to the constant error model in our dataset.