Comparisons of thyroid hormone withdrawal and rhTSH aided 1850 MBq and 3700 MBq radio iodine (RAI) post-surgical remnant ablation in differentiated thyroid cancer (DTC)

Objectives To compare the successful thyroid remnant ablation rate of 1850 MBq and 3700 MBq 131I prepared with thyroid hormone withdrawal (THW) and recombinant human thyroid stimulating hormone (rhTSH) in patients with DTC.

Methods 732 DTC patients after total/near total thyroidectomy were consecutively assigned to the 3 treatment groups: in the 1st group, patients (n =218) were ablated with 1850 MBq RAI after THW; in the 2nd group, patients (n =141) were ablated with 3700 MBq RAI after THW; in the 3rd group, patients (n =373) were ablated with 1850 MBq RAI after rhTSH. The outcome of thyroid remnant ablation was retrospectively compared by conventional 131I scan and/or serum thyroglobulin (Tg) in the absence of Tg-antibody performed under TSH stimulation 2-27 months after ablation.

Results At the first follow-up, Tg < 2ng/mL was in 173 out of 218 patients (79.4%) received 1850 MBq RAI under THW, 110 out of 141 (78.0%) received 3700 MBq RAI under THW and 321 out of 373 (86.1%) received 1850 MBq RAI under rhTSH stimulation 1st group, 98/141(69.5%) in the 2nd group and 277/373 (74.3%) in the 3rd group, respectively (p=0.005). When successful thyroid remnant ablation was defined as “no visible uptake in the thyroid bed” in diagnostic 131I scan, 155 of 196 (78.1%) patients in the 1st group, 88 of 113 (77.9%) patients in the 2nd group, 226 of 290 (77.9%) patients in the t3rd group were successfully ablated (p=0.707). After a significant period of follow-up (24.22±13.53 in rhTSH group, 38.77±22.83 in 1850 MBq THW and 60.33±35.98 in 3700 MBq THW, respectively), a significant lower recurrence was observed in patients prepared with rhTSH (7%) compared with 1850 MBq (11%) and 3700 MBq (12%) under THW.

Conclusions 1850 MBq RAI after THW or rhTSH is equally effective as 3700 MBq after THW for thyroid remnant ablation in DTC patients. 1850 MBq RAI under rhTSH is recommend for post-surgical ablation and is safe, effective and avoids hypothyroidism.

Research Support Alberta Cancer Foundation, Canada Foundation for Innovatio