Can we safely reduce the administration of 131-iodine in patients with differentiated thyroid cancer? – experience of the Brugmann hospital in Brussels

Abstract

Background 131-iodine (131I) administration after surgery remains a standard practice in differentiated thyroid cancer (DTC). In 2014, the American Thyroid Association presented new guidelines for the staging and management of DTC, including no systematic 131I in patients at low-risk of recurrence and a reduced 131I activity in intermediate risk. The present study aims at evaluating the rate of response to treatment following this new therapeutic management compared to our previous treatment strategy in patients with DTC of different risks of recurrence. Methods Patients treated and followed up for DTC according to the 2014-ATA guidelines (Group 2) were compared to those treated between 2007 and 2014 (Group 1) in terms of general characteristics, risk of recurrence (based on the 2015-ATA recommendations), preparation to 131I administration, cumulative administered 131I activity and response to treatment. Results In total, 136 patients were included: 78 in Group 1 and 58 in Group 2. The two groups were not statistically different in terms of clinical characteristics nor risk stratification: 42.3% in Group 1 and 31% in Group 2 were classified as low risk, 38.5% and 48.3% as intermediate risk and 19.2% and 20.7% as high risk (P=0.38). Two patients (one in each group) with distant metastases were excluded from the analysis. Preparation to 131I administration consisted in rhTSH stimulation in 23.4% of the patients in Group 1 and 100% in Group 2 (p<0.001). 131I was administered to 46/77 patients (59.7%) in Group 1 (5 at low risk of recurrence) and 38/57 patients (66.7%) in Group 2 (0 with a low risk). Among the patients treated by 131I, median cumulative activity was significantly higher in Group 1 (3.70GBq [100mCi] range 1.11-11.1 GBq [30-300 mCi]) than in Group 2 (1.11 GBq [30 mCi], range 1.11-7.4 GBq [30-200 mCi], P<0.001). Complete response was found in 90.9% in Group 1 vs. 96.5% in Group 2 (P=0.20). Conclusions Using the 2015-ATA evidence-based guidelines for the management of DTC, meaning no 131I administration in low-risk patients, a low activity in intermediate and even high risk patients, and a systematic use of rhTSH stimulation before 131I therapy allowed us to reduce significantly the median administered 131I activity, with a similar rate of complete therapeutic response.