Diagnostic whole-body scanning before radioiodine therapy for pulmonary metastases of differentiated thyroid cancer: predictive value and recommendations.

RATIONALE: Radioiodine therapy improves the survival of patients with pulmonary metastases of differentiated thyroid cancer (DTC). It is controversial whether the diagnostic whole-body I-131 scan (DWS) before therapy is essential. We determined whether DWS could predict the efficacy of I-131 therapy for pulmonary metastases.

METHODS: We undertook a retrospective review of records of 42 patients (28 women and 14 men, mean age 52.7 years). The patients had received 62 rounds of I-131 therapy for lung metastases of DTC at our institution between June 2002 and June 2006. On the same day that the DWS (dose of 185 MBq) (5 mCi) was completed, the patient received I-131 therapy (dose of 3700-7400 MBq) (100-200 mCi). Post-therapy whole-body scans (PWS) were performed after 3 to 4 days and 7 to 8 days. For all therapies, chest CT images were obtained before I-131 therapy, and 3 and 6 months after therapy for evaluation of therapeutic effectiveness. In addition, serum thyroglobulin (Tg) values were measured before and after the radioiodine therapy for all treatments.

RESULTS: In the group demonstrating I-131 accumulation for pulmonary metastases on DWS, 72% of patients showed a reduction of pulmonary metastases on follow-up CT. On the other hand, in the group that failed to accumulate I-131 on DWS, only 5% of patients showed a reduction of pulmonary metastases. After therapy, serum Tg levels decreased significantly in the group that initially showed accumulation of I-131 in DWS (P = 0.045). In contrast, no remarkable changes between pre- and post-therapy Tg levels were observed in patients who failed to accumulate I-131 in DWS.

CONCLUSION: A whole-body I-131 diagnostic scan before I-131 therapy has a predictive value for the efficacy of therapeutic radioiodine treatment for pulmonary metastases of differentiated thyroid cancer.