Analysis of the Correlation between the Radioactive Iodine Activity and Neutrophil-to-Lymphocyte Ratio in Patients with Differentiated Thyroid Cancer

SIMPLE SUMMARY: A higher tumor burden in patients with differentiated thyroid cancer undergoing radioactive iodine ((131)I) therapy may release into the bloodstream large amounts of (131)I with a long residence time. We hypothesized that after the (131)I intake, the blood concentration of (131)I shows a course in several phases. To our knowledge, this research is the first of its kind. The results of the current study demonstrated a (131)I blood concentration biphasic course. The time points to be considered are 46 and 69 h. (131)I uptake in the residual thyroid tissue peaked after 46 h. The positive correlation between the neutrophil-to-lymphocyte ratio and administered (131)I activity or the blood activity shows that the time interval between 46 and 69 h should be associated with the release of hematological inflammatory mediators, such as neutrophils and lymphocytes, to eradicate tumor cells in response to (131)I therapy. ABSTRACT: Publications investigating the effect of radioactive iodine ((131)I) therapy on the circulating peripheral blood cells in patients with differentiated thyroid cancer (DTC) are limited to blood samples collected more than 92 h after (131)I. Studies conducted on blood samples collected up to 92 h are rare due to the radioactive contamination risk. This research aimed to assess the relationship between the prescribed (131)I activity, human whole blood activity, and peripheral blood cells at many time points (6, 22, 46, 69, and 92 h after (131)I). The study enrolled 50 female patients with DTC who received a (131)I median activity of 90.54 mCi (3.35 GBq). The neutrophil-to-lymphocyte ratio (NLR) was measured as an inflammatory marker. (131)I uptake in the residual thyroid tissue peaked after 46 h. Blood activity decreased in the first 46 h and increased 69 h after the (131)I intake. Blood activity was associated with the absolute lymphocyte count and the NLR at 69 h (r = −0.49 and r = 0.52, p < 0.001). Our results demonstrate that the time interval between 46 and 69 h should be associated with the release of hematological inflammatory mediators, such as neutrophils and lymphocytes, to eradicate tumor cells in response to (131)I therapy.