Nuclear medicine approaches in the monitoring of thyroid cancer patients.

PURPOSE: To evaluate the role of some nuclear medicine approaches such as (99m)Tc-MIBI scan and (131)I whole-body scintigraphy (WBS) in the monitoring of patients with differentiated thyroid cancer (DTC).

PATIENTS AND METHODS: 95 patients (69F/26M) aged 17-74 years (mean 44.2) with DTC (56 cases with papillary, 20 with follicular and 19 with papillary-follicular carcinoma) were assessed. All of them had undergone total or near-total thyroidectomy and received radioiodine treatment for ablation of post-surgical residual thyroid tissue. They were examined after 4 weeks of L-thyroxin withdrawal in the follow-up of DTC. Planar and whole-body images were acquired at 15 and 180 min after i.v. administration of (99m)Tc-MIBI (555-740 MBq) and at 48 h after p.o. administration of(131)I(111-185 MBq) on Toshiba GCA gamma camera. Serum thyroglobulin (Tg) estimations were performed to clarify the presence of residual normal tissue or recurrent malignancy.

RESULTS: (131)I scan was positive in 63 patients showing thyroid remnants in 31 cases, lymph node metastases in 24 cases (17 to the neck, 7 to the neck/mediastinum), pulmonary metastases in 6 cases, bone and brain lesions in 2 cases. In 15 patients (131)I scan was negative, Tg was undetectable, so patients were considered tumor-free. In 17 patients (131)I scan was negative while serum Tg was increased. These false negative results were observed predominantly in cases with less differentiated metastatic disease, especially after several courses of high-dose (131)I therapy. (99m)Tc-MIBI scan revealed the presence of lymph node and/or lung metastases (non-functioning metastases) in 14 of them, false negative results were obtained in 2 cases, and one false positive in 1 case. Serum Tg was increased in all patients with local lymph node and distant metastases, visualized by (131)I or by (99m)Tc-MIBI, but also in 18 patients with thyroid remnants only.

CONCLUSION: (99m)Tc-MIBI scan has been reported to be a highly sensitive technique for the detection of DTC metastases that have lost the capability to uptake (131)I; the combined (99m)Tc-MIBI scintigraphy and serum Tg estimation appear to be an alternative method of radioiodine imaging in cases with DTC and elevated Tg.