Differentiated thyroid carcinoma (DTC) follow up: A 131I-SPECT/CT study

Objectives To evaluate whether ¹³¹I-SPECT/CT may have an additional value over planar scan in identifying residues, local and distant metastases.

Methods We studied 202 thyroidectomized DTC pts: 188 had ¹³¹I diagnostic and 14 post-therapeutic planar and SPECT/CT scan by an hybrid dual head gamma camera. An incremental value was assigned to SPECT/CT when it provided a better iodine uptake foci identification and interpretation, a more correct anatomic localization and characterization and a precise tumor lesion differentiation from physiological areas.

Results Planar evidenced 151 foci in 70/202 pts, SPECT/CT 204 foci in 79/202 pts confirming those seen at planar, but also identified 37 occult foci in 14/70 pts; 6 occult foci were seen at SPECT/CT in 9/202 further pts negative at planar. SPECT/CT correctly characterized 58 foci unclear at planar and classified as neoplastic foci for which planar excluded malignancy, discriminating residues from lymph node metastases in the neck some of which adjacent to salivary glands missed by planar. SPECT/CT also detected occult metastases in mediastinum, abdomen/pelvis and bone. Globally, SPECT/CT detected more foci than planar in 11.4% of pts, including 4.5% completely negative at planar. Moreover, SPECT/CT had an incremental value in 65.8% of pts, modified therapeutic management in 34.1% of positive cases and clarified physiologic areas also avoiding unnecessary treatment in 16.4% of pts with only a focus.

Conclusions ¹³¹I-SPECT/CT improved planar scintigraphy interpretation, reducing false positive and providing a higher accuracy in tumor identification; it was able to change therapeutic management defined by planar, including radioiodine dose, and resulted surgical planning reliable guide.