The quantitative comparison of low dose and standard dose radioiodine therapy effectiveness in patients with low risk differentiated thyroid cancer

Full text of publication follows. Background: Currently, the lower dose radioiodine administration instead of standard 3700 MBq for low-risk differentiated thyroid cancer (DTC) is discussed. In this study, we compared the results of postoperative I-131 remnant ablation using a quantitative data in the low activity (1110 MBq; 30 mCi) and standard dose (3700 MBq; 100 mCi). Patients and Methods: The study included two groups of patients with low risk differentiated thyroid cancer: group 1 included 43 patients who were treated with 30 mCi I-131 and group 2 included 32 patients treated with 100 mCi (control group) for postoperative thyroid remnant ablation. In both groups, following a near total or total thyroidectomy, postoperative thyroid remnants of all patients were assessed with thyroid uptake test (TUT). Whole body scans (WBS) of all patients were performed in 7-10 days after the administering I-131 treatment for the ablation of residual thyroid. We obtained counts from ROI (region of interest) analysis of several regions (thyroid bed, liver, thigh and whole body). Thyroid/liver ratios were calculated by comparing counts that in the thyroid region to that in the liver. After the 6. month whole body scans after the treatment was performed to 52 patients (24 patients of group 1 and 28 patients of group 2) for evaluating the success of ablation treatment. Results: A significant difference in pretreatment TUT and thyroid remnant counts in post treatment scans wasn't found between both groups (p>0.05). However, in post treatment scans, liver, thigh, whole body count were significantly higher and thyroid/liver ratio was significantly lower in group 2 compared with group 1 (p<0.001). Although the percentage of ablation based on the 6. month scans was higher in group 2 compared with group 1 (25 of 28 patients, 89.3% versus 17 of 24 patients, 70.8%), statistical difference was not significant (p>0.05). Conclusion: In low risk DTC patients, low dose radioactive iodine can ablate thyroid remnant as effectively as a higher dose with other non-target organs and whole body less exposure to radiation. (authors)