Predictive value of FDG PET at initial radioiodine therapy for survival of high-risk patients with differentiated thyroid cancer

Objectives We evaluated the predictive values of FDG PET and radioiodine uptake at initial radioiodine therapy (RIT) in high-risk patients with differentiated thyroid cancer (DTC).

Methods 141 high-risk patients with DTC were retrospectively analyzed. All patients underwent initial RIT after total thyroidectomy (patients had not received any previous radioiodine treatments) and received at least one further course of RIT due to suspected or proven metastases. FDG PET performed before initial RIT and I-131 scans were evaluated for pathologic extrathyroidal uptake. Biochemical response was assessed by changes of TSH-stimulated serum thyroglobulin (Tg) between the first and second RIT (ΔTg).

Results Biochemical response could be evaluated in 80 patients, survival data could be obtained for 88 patients (range 6 - 124 months). Regarding radioiodine uptake, biochemical response was significantly better in patients with radioiodine-positive metastases compared to patients with radioiodine-negative metastases (median ΔTg I+: 55.8% vs I-: 112.6%, p<0.01). However there was no significant difference regarding long-term overall survival (OS I+: 61.3% vs I-: 58.2%, p>0.05), though deaths occurred later in patients with radioiodine-positive metastases compared to radioiodine-negative patients (p<0.05). Regarding FDG uptake at initial RIT, patients with FDG-positive metastases showed a poorer biochemical response compared to patients with FDG-negative metastases (median ΔTg FDG+: 77.5% vs FDG-: 53.2%, p<0.05), and these two groups also differed significantly regarding long-term survival (OS FDG+: 48.5% vs FDG-: 100.0%, p<0.05).

Conclusions At initial RIT, FDG PET is more predictive for long-term survival, whereas radioiodine uptake is more important for short-term response. FDG PET performed at initial RIT might represent a useful tool for management of high-risk patients with DTC.

Research Support Deutsche Röntgengesellschaft (DRG), Japanese-German Radiological Affiliation (JGRA)