SPECT/CT in the Treatment of Differentiated Thyroid Cancer

Abstract

Single-photon emission computed tomography with integrated computed tomography (SPECT/CT) systems has been applied in a wide range of clinical circumstances, and differentiated thyroid cancer (DTC) is one of the most important indications of SPECT/CT imaging. In the treatment of DTC, SPECT/CT images have been reported to have many advantages over conventional planar whole-body scintigraphy based on its precise localization and characterization of abnormal foci of radioactive iodine (RAI) accumulation, influencing the staging, risk stratification, and clinical management as well as reader confidence. On the other hand, SPECT/CT has limitations including additional radiation exposure from the CT component, additional imaging time, and cost-related issues. Each SPECT/CT image acquired at different time points throughout the management of DTC may have a different clinical meaning and significance. This review article addresses the clinical usefulness of RAI SPECT/CT images acquired during the pre-ablation period, post-therapy period, and long-term follow-up period, respectively.

Keywords: Differentiated thyroid cancer; Long-term follow-up period; Post-therapy period; Pre-ablation period; Radioactive iodine; SPECT/CT.

Fig. 1

A 55-year-old female patient underwent total thyroidectomy with central neck dissection and was diagnosed as having papillary thyroid cancer (pT3N1aM0, stage III). a Post-therapy radioactive iodine (3.7 GBq of I-131) whole-body scan showed several foci of tracer uptake in the neck. b–d SPECT/CT images clearly demonstrated multilevel metastatic lymph nodes (level II–IV) in the right neck, which altered nodal stage from N1a to N1b. e–g CT component from SPECT/CT also showed small lymph nodes with slight high attenuation in the corresponding right neck (arrows). Eight months later, however, her diagnostic radioactive iodine whole-body scan and neck ultrasonography showed negative findings and stimulated serum thyroglobulin was less than 1 ng/ml. Post-therapy SPECT/CT findings altered nodal stage, but did not lead to changes in patient management

Fig. 2

A 46-year-old female patient underwent rib excision for an incidentally found rib mass and was diagnosed as having metastatic thyroid cancer. Subsequently, she underwent total thyroidectomy with central neck dissection, and the pathologic result was intrathyroidal microscopic papillary carcinoma with one central neck node metastasis (pT1N1aM1, stage IV). a Post-therapy radioactive iodine (5.55 GBq of I-131) whole-body scan showed three unexpected foci of tracer uptake in the left shoulder and abdomen. b–d SPECT/CT images clearly demonstrated bone metastasis of the left scapula and two metastatic nodules in the omentum and retroperitoneum. e–g Retrospective review of preoperative F-18 FDG PET/CT showed two small high-attenuating nodules without significant FDG uptake in the corresponding abdominal areas (arrows), but no abnormal FDG uptake in the left scapula. Laparoscopic excision for the omental and retroperitoneal mass was done 1 month later, and metastatic thyroid cancer with cystic change was confirmed at pathologic findings. Her stimulated serum thyroglobulin gradually decreased from 270.2 ng/ml at the pre-ablation period to 26.1 ng/ml. Post-therapy SPECT/CT findings did not change the TNM staging, but contributed to changes in patient management by detection of unexpected metastatic lesions