High dose 123I imaging as a predictor of 131I post-therapy scan outcome in differentiated thyroid cancer (DTC)

Abstract

Aim: To test prospectively 123I imaging follow-up of DTC. Method: One hundred and seven studies were evaluable in 82 patients (female/male ratio 3.5:1, papillary/follicular/mixed/hurtle cell tumour ratio 13:5:2:1) using 185 MBq 123I imaging at 2 and 24 h. Results: Seventy-four studies were 123I negative (51 6 months post-ablation, 23 post-previous 131I therapy). Four showed high thyroglobulin with radiology/MIBI evidence of disease but no further 131I treatment given. Seven studies were positive (4 completed 131I therapy, 3 awaiting therapy). Twenty-six patients had both 123I imaging and 131I therapy. Twenty-two were 123I positive and post-131I therapy scan positive (greater uptake with 131I than 123I in 4). Three studies were 123I negative, post-131I therapy scan negative. One patient 123I negative with low TSH had post-131I therapy scan positive three months later. Combining these 26 studies with our previous 17 similar studies including 131I tracer negative scans gave 36 concordant 123I pre/131I post-therapy positive scans, 5 concordant negative scans and 2 discordant results, 43 studies, χ2=28, P<0.001. Conclusion: High dose 123I imaging is an excellent predictor of the post-131I therapy scan and when strategically combined with thyroglobulin has replaced 131I tracer studies in our follow-up of DTC.