Optimizing high dose therapy (HDT) I-131 (RAI) whole body scans (WBS) in patients with DTC – Part A

Abstract

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Objectives: HDT-RAI WBS in DTC is considered highly efficient in demonstrating residual/recurrent disease. However, findings vary with scanning time intervals (TI) commonly up to 2w post RAI (~ 7d in our dept). The goal was to demonstrate possible WBS-TI changes to optimize WBS results.

Methods: Study group included 33 DTC pts (24F, 9M, mean age 51y) who had early & delayed TI-WBS using dual-head gamma-cameras equipped with high energy collimators. Each pt WBS were compared, and analysed for site changes.

Results: Two HDT groups were identified. Group A: 16 pts with HDT for thyroid remnants ablation (mean 99 mCi dose) who had WBS at 3.6 and 7.4 d (mean). Group B: 17 pts with HDT for disease recurrence (mean 190 mCi dose) with WBS at 3.8 and 7.3 d (mean). Finally, 85 sites were identified. Group A: 28 sites seen: 24 in the thyroid bed/pyramidal lobe; 4 in lymph nodes. Group B: 57 sites seen: 11 in the thyroid bed/pyramidal lobe. 46 in lymph nodes, lungs, bones, and others. Early and delayed WBS analyses showed no TI changes in 38.8% of lesions. Positive TI changes were seen on 7d WBS in 61.2%: decreased activity in 17.7%, increased in 34.1%, and new sites in 9.4%. Group A: No changes in 39.2%; decreased in 35.7%; increased in 10.7%; new sites in 14.4%. Group B: No difference in 38.5%; decreased in 8.8%; increased in 45.7%; new sites in 7.0%. Thyroid remnants/pyramidal lobe were seen better on early WBS while delayed scans showed significant increase/new sites in lungs, lymph node mets in 45.5%,and in group B in 52.7%.

Conclusions: WBS-TI considerations should include the imaging changes with time. Since a single TI is preferred, an intermediate (~5 days) WBS is recommended. A prospective study is currently underway to verify this concept.