Low FDG metabolic activity of Loco-regional recurrence in thyroid cancer patients; Is Iodine-131 has a potentiality?

Abstract

Purpose: To investigate the impact of quantitative FDG-Metabolic activity of non-iodine avid Loco-regional recurrence [LRR; thyroid recurrence and/or cervical node metastasis] on therapy selection in thyroid cancer patients with elevated thyroglobulin [TG]. Methods: Forty thyroid cancer [33 papillary and 7 follicular] patients who underwent FDG PET/CT were studied [with TSH>30 mU/L]. Those with only LRR were classified according to maxSUV [cut-off level 5] into high and low metabolic activity lesions [HMA &LMA]; their therapy outcome was compared with histopathologic findings and/or follow-up routine evaluation. Results: Only LRRs was found in 20 patients [17 papillary and 3 follicular] with diagnostic accuracy of FDG PET/CT of 100%. 14/20 patients belonged to HMA where surgical neck exploration was done while in the remaining 6 patients with LMA empirical high dose of radioactive iodine-131 was given based on the assumption of the presence of a mixture of undifferentiated and differentiated thyroid cancer cells; though their post-therapy scan was negative but declined TGlevels were elicited in their follow-up [base-line 27.7±2.4 and at follow-up 6.8±1.4 ng/ml; P 0.02]. Conclusion: Max-SUV based classification of non-iodine avid LRR might improve the diagnostic accuracy FDG PET/CT in a therapeutically relevant way in DTC-patients by precisely localizing them with subsequent surgical guidance in HMA lesions while those with LMA could benefit from further RA-131 therapy.