Comparative evaluation of early and late whole body scan images post-therapy with I131 in patients with differentiated thyroid cancer

Aim: In order to reduce the period of time between the therapy with I131 and the acquisition of images for Whole Body Scan (WBS), the aim of this investigation is the comparison of WBS images acquired early (4th-6th days) and late (10th-15th days). Materials and Methods: 15 patients whit the diagnosis of Differentiated Thyroid Carcinoma (Follicular and Papillary) were included in the study. All of them received a therapeutic dose of Iodine 131 of 100 mCi. WBS images were obtained in one early control -4th - 6th day- and after 10-15 days post-therapy -late control-, using an SPECT system General Electric Starcam 3200 AC/T. The WB images were acquired in 512x128 matrix for anterior and posterior views. Their evaluation was performed blind and independently by 3 Nuclear Medicine Physicians, classifying the cases according a checklist 'with changes or without changes'. The signification of the results was evaluated by McNemar non parametric Test, using a significance level alfa=0.05. Results: 60% of patients showed some change between early and late controls. The change consisted of important descending or complete disappearance of I131 uptake focus in late control comparing with early evaluation. In the 33.3% of cases (44% of focus) is possible to observe total disappearance of focus described early. In 4 patients there were extra thyroidal metastasis, they didn't present reduction in their intensity of uptake and in one case the focus increased the uptake. Likewise, there was possible to determine the frequency of observation for the uptaking of Iodine 131 in normal sites. Conclusion: The changes observed between early and late evaluations an unacceptable loss of information which support the idea in order to evaluate with WBS images to the patient early (4th-6th day). This change is very appreciated in order to reduce the period between the therapy and control and it's a favourable support for the aim of this investigation