Evaluation of 131I scintigraphy and stimulated thyroglobulin levels in the follow up of patients with DTC: a retrospective analysis of 1420 patients

Gonzalez Carvalho J., Görlich D., Schober O., Wenning C., Riemann B., Verburg F., Vrachimis A.

Abstract

Aim: To study the clinical yield of diagnostic whole body 131I scintigraphy (DxWBS) in the follow-up of differentiated thyroid carcinoma (DTC) patients in relation to stimulated thyroglobulin (sTg) in the initial post-ablation setting, as well as in the setting of repeated monitoring in course of further DTC follow-up. Methods: Data of 1420 thyroidectomized and radioiodine remnant-ablated DTC patients following a well-defined therapy and standardized follow-up protocol were evaluated. DxWBS and sTg were evaluated separately and in combination for various follow-up time points. The factual administration of the recorded indication for further oncologic therapy (excluding radioiodine therapies given for minimal normal remnants) within the following 4 months after follow-up served as the standard of reference. Furthermore, DxWBS was compared to post therapy WBS and SPECT(/CT) if available. Subgroup analysis was carried out for DTC patients < 45 years old at diagnosis without distant metastasis. The diagnostic impact of cervical ultrasound was not assessed. Results: sTg can identify the patients at risk better than DxWBS. Furthermore, the most sensitive time point to assess response appears to be a time point beyond 3 months after RRA. When information received from both imaging and laboratory measurements are concordant, i.e. both construe absence of remaining disease, only a small fraction of patients (<2%) required treatment in the future. The strongest effect was observed 12 months after RRA. Only 0.9% of the negative DxWBS patients with concordant sTg below the functional sensitivity at this time point required treatment thereafter. Conclusion: A complete omission of DxWBS in the post-RRA surveillance of DTC is justified once DxWBS is negative and sTg is below the functional sensitivity (with no evidence of thyroglobulin antibodies), as patients showing this combination of test results (especially 12 months after RRA) show an at worst marginal risk of recurrence. In all other cases DxWBS may still be justified.