The management of differentiated thyroid cancer using 123I for imaging to assess the need for 131I therapy.

Background Follow-up of 131 I whole-body scanning after 131 I ablation is associated with potential stunning. Previous studies have suggested that, for scanning, 123 I is more sensitive than 131 I in identifying thyroid tissue, but its specificity when positive is less certain. Aim The use of 123 I as an imaging agent in place of serial 131 I imaging has been evaluated in the surveillance and treatment of differentiated thyroid carcinoma. Results A total of 186 studies in 136 patients with differentiated thyroid carcinoma were evaluated after total or near total thyroidectomy followed by 131 I ablation. In 125 studies 123 I scanning was negative and no 131 I therapy was given; four patients were positive on 123 I scanning but for other reasons no 131 I therapy was given. In 48/49 patients a positive 123 I scan was followed by positive 131 I therapeutic uptake. Only one patient failed to show positive uptake of 131 I when first treated and she subsequently demonstrated uptake on a second therapy. Conclusion High-dose 123 I imaging is the correct predictor of the 131 I post-therapy scan findings in most cases, at an administered activity that avoids stunning. As a diagnostic agent it is preferable to 131 I in differentiated thyroid carcinoma.