[Diagnostic scintigraphy and effectiveness of 131I radioiodine therapy in differentiated thyroid carcinoma (DTC)]

Since the effect of pre-therapeutic scintigraphy on the outcome of DTC treatment is debated, we evaluated factors affecting the effectiveness of (131)I therapy with respect to the delay between diagnostic scintigraphy and the application of radioiodine.

In the studied group of 60 patients with DTC, mean age 54.6 +/- 13.0 years, four weeks prior to the planned diagnostics, L-thyroxine was withdrawn and the following tests performed: (131)I (4 MBq) uptake above the neck, thyroid volume by USG, TSH and hTg level. Wholebody scintigraphy (37 MBq) was performed. The time between this diagnostic scintigraphy and application of (131)I (3657 MBq) was calculated. Based on whole-body 131I scintigraphy (74 MBq) performed 1 year after radioiodine treatment, the patients were divided into: group I - 42 patients with no tracer accumulation, and group II--18 patients who continued to accumulate (131)I in the neck.

The differences between the median values of (131)I uptake and of thyroid volumes, and between the TSH and hTg median values in the two groups of patients were found not to be statistically significant. The average times between diagnostic scintigraphy and (131)I treatment in group I and II (9.4 vs. 8.3 weeks, respectively) were not significantly different either.

Despite the different effectiveness of supplementary (131)I treatment, patients in group I and group II showed no statistically significant differences in the studied parameters. It appears that the diagnostic (131)I activity of 37 MBq and the time between diagnostic scintigraphy and application of (131)I did not have any effect on the results of the treatment in our group of patients.