Recombinant human thyrotropin (rhTSH) versus Levo-thyroxine withdrawal in radioiodine therapy of differentiated thyroid cancer patients: differences in abdominal absorbed dose.

PURPOSE: In DTC patients, 131-radioiodine therapy has routinely been used for many years for thyroid remnant ablation after thyroid surgery. To date, two different strategies can be used to achieve sufficient TSH stimulation on thyroid remnant: (I) Levo-thyroxine withdrawal or (II) rhTSH stimulation. The aim of our study was to compare the abdominal absorbed dose ratio between differentiated thyroid cancer patients who underwent thyroid remnant ablation after either L-T4 withdrawal or rhTSH stimulation.

METHODS: We reviewed the records of 63 patients affected by differentiated thyroid cancer. All patients underwent thyroid remnant ablation after either L-T4 withdrawal or rhTSH stimulation. A post-therapy whole-body scan was obtained 5 days after 131-radioiodine therapy. Qualitative and quantitative image analysis was performed. Quantitative analysis was performed by drawing seven regions of interest on the abdomen (anterior and posterior views) to estimate both the activity ratio (AR) and absorbed dose ratio (DR) obtained in patients treated in hypothyroidism or after rhTSH stimulation.

RESULTS: The values of the activity and absorbed dose ratios obtained on each abdomen region (liver, stomach, ascending colon, transverse colon, descending colon, rectum, and small intestine) were always higher in patients treated after L-T4 withdrawal than after rhTSH stimulation with p-values of 0.000, 0.000, 0.001, 0.000, 0.022, 0.007, and 0.002, respectively.

CONCLUSIONS: DTC patients treated with 131-radioiodine after rhTSH stimulation have lower abdominal radioiodine activity than hypothyroid patients. Our data could be of practical relevance in terms of patient management. The potential impact on rare radioiodine-related gastrointestinal side effects is to be established in specifically designed prospective studies.