Estimation of intake by maximum likelihood method using follow up measurements of 131I thyroidal burden

131I is widely used for diagnostic and therapeutic purposes. Since thyroid is the main deposition site for 131I, so it can be detected by direct thyroid monitoring. This work presents results of follow-up measurements of an individual who was internally contaminated with 131I with injected activity being determined by maximum likelihood method. Importance of dose per unit content is also shown in this study. The whole body monitoring system available in Radiation Safety Systems Division of Bhabha Atomic Research Centre is calibrated for estimation of 131I in the thyroid of radiation worker using BOttle MAnnikin Absorber (BOMAB) phantom with neck part being replaced by American National Standards Institute (ANSI)/International Atomic Energy Agency (IAEA) neck. The estimated intake was found to be 89.24 kBq and the committed effective dose is calculated as 1.96 mSv. The data are analyzed with autocorrelation and Chi-square test to establish goodness of fit with log-normal distribution. The overestimation of thyroid activity by use of mid axial hole in BOMAB phantom is removed by using ANSI/IAEA neck phantom. Measured retained thyroidal data on different days following the intake has closely fitted to the ICRP predicted retained activity. (author)