Alternative radiopharmaceuticals to radioiodine in the follow-up of thyroid cancer

131I-whole body scan (WBS) is a sensitive and highly specific method in detecting local recurrence and distant metastases during the follow-up of differentiated thyroid cancer (DTC). However, in selected clinical situations other radiopharmaceuticals (RF) can be useful. The utility of the various RF and the clinical setting in which they can be recommended are discussed. . 99mTc-pertechnetate (TcO4−) is mainly used for the evaluation of thyroid nodules; there is no significant utility in the follow-up of DTC. However, even though there are cases reported of metastatic lymph node visualization in patients no submitted to thyroidectomy. . 99mTc-MIBI may be useful in determining local node metastases in well-differentiated thyroid cancer. Its affinity for mitochondria makes sestamibi especially attractive as imaging agent for the mitochondria-rich, even thogh poorly iodine-concentrating Hurtle cell carcinoma. . 201 Tl appears to be an excellent tracer for detecting local metastases and cervicomediastinal metastatic lymph nodes and, to a lesser extent, lung metastases. 201Tl is less sensitive than 131I in detecting residual thyroid tissue postoperatively. Like Sestamibi, Thallium imaging can be performed while a patient is on L-thyroxine suppression; SPECT may improve the visualization of deeply located metastases. . To date there are several studies demonstrating higher FDG uptake in poorly differentiated tumors and in patients with higher pT stage; while a relatively low sensitivity of FDG might be expected in highly differentiated thyroid carcinoma. The phenomenon of an alternating uptake pattern of FDG and 131I in poorly differentiated tumous is well known and has been referred to as “flipflop” pattern. Alternative radiopharmaceuticals to radioiodine can be used during the follow-up of thyroid cancer in the following circumstances: 1. Patients with DTC, elevated Tg levels and negative 131I-WBS; 2. Suspected false positive images during 131I-WBS; 3. Poorly differentiated or anaplastic thyroid cancer; 4. Selected histotypes (i.e. Hurtle cell carcinoma); 5. Detection of metastases in patients while under thyroid suppression.