Comparison of ¹²³I and ¹³¹I for Whole-Body Imaging in Thyroid Cancer

Abstract

We compared the diagnostic sensitivities of ¹²³I and ¹³¹I whole-body imaging in differentiated thyroid cancer. Methods: Twelve thyroidectomized patients (3 previously treated with ¹³¹I) were studied. After a period of thyroid hormone withdrawal, whole-body imaging was performed approximately 24 and 72–96 h after administration of 74–185 MBq (2–5 mCi) ¹²³I and 111–185 MBq (3–5 mCi) ¹³¹I, respectively. Results: Both ¹²³I and ¹³¹I revealed residual thyroid tissue, present in 9 patients. ¹³¹I detected metastases in 5 studies of 4 patients. In 4 of 5 studies, ¹²³I missed metastases shown by ¹³¹I in 8 body regions including the neck, mediastinum, lungs, and bone and detected 3 other sites of metastasis only in retrospect. No lesion was better seen with ¹²³I than with ¹³¹I. Conclusion: Although ¹²³I is adequate for imaging residual thyroid tissue, it appears to be less sensitive than ¹³¹I for imaging thyroid cancer metastases.