Selection of the Optimal Scanning Agent for Thyroid Cancer

Abstract

Physical and biologic principles, availability, and experience in use determine which radiopharmaceuticals will be the optimal agents to portray scintigraphically thyroid cancers. However, clinical reasoning must dictate which scanning procedure to use and when. To identify functioning thyroid nodules, and thereby exclude malignancy and also disclose the source of excess thyroid hormone, technetium Tc 99m pertechnetate is the agent of choice. To evaluate patients with metastatic differentiated thyroid cancer (DTC) for possible radiopharmaceutical therapy, low doses (no more than and probably less than 74 MBq or 2 mCi) of 131I iodide are preferred. 131I is especially necessary if dosimetry is undertaken to help prescribe the optimal therapeutic dose of 131I. For less well differentiated tumors that do not concentrate 131I, most experience has been with thallium 201, which enables depiction of most metastases, but, in time, newer agents may be found to produce superior scans. The goal of imaging of the less well differentiated cancers must be to direct additional therapy such as external beam radiation of surgical excision. It is unlikely that any scanning procedure that depends on the physiologic and biochemical activities of DTC will have as much sensitivity for locating tumors in the euthyroid as in the hypothyroid patient. A majority of medullary carcinomas of the thyroid (MCT) have been portrayed by indium 111 octreotide and by 99mTc pentavalent dimercaptosuccinic acid; other agents have concentrated to lesser levels in the tumors or have not been investigated as extensively. As of now, metastatic MCT defies therapy, and, therefore, scanning to detect the tumors has little clinical utility.

Evaluation of thyroid nodules with technetium‐99m MIBI and technetium‐99m pertechnetate

“…Pertechnetate static scans (without the first two phases) showed a low differential diagnostic value between malignancy and benign lesions. 12 As a result, 20 T1 was used for the preoperative evaluation of thyroid nodules, and differentiation between malignant and benign tissue was not possible.…”

Current Controversies in the Management of Pediatric Patients with Well-Differentiated Nonmedullary Thyroid Cancer: A Review

“…Ideally, the serum TSH should be more than 25 mU/mL to optimize iodine uptake by the remnant (9,36,60). Immediately prior to remnant ablation, we, and others, have used in children either a 0.5-2 mCi (18-74 MBq) 131 I or 300-400 mCi (11.1-14.8 MBq) 123 I diagnostic WBS to delineate the extent and location of the thyroidal remnant (65)(66)(67)(68)(69). Several experts in the field also include at this stage a screening chest CT scan, performed without iodinated intravenous (IV) radiographic contrast, to monitor for possible lung metastases (70).…”

Use of Radiopharmaceuticals in Diagnostic Nuclear Medicine in the United States

“…The administered activity of 131 I-sodium iodide for thyroid imaging before the mid-1970s was about 1.85 MBq (Harper et al 1965; Wagner 1968; Atkins 1975; McAfee and Subramanian 1984; Drozdovitch et al 2014), then gradually increased to 3.7 MBq (Sodee and Early 1975; Irwin et al 1978; Mettler et al 1986; Sisson 1997). The administered activity of 123 I-sodium iodide for thyroid imaging before the late-1970s was estimated to be 3.7 MBq (Robertson 1982; Wagner et al 1986), then gradually increased to 11.1 MBq in the 1980s (Mettler and Guiberteau 1983, Mettler et al 1986; Wagner et al 1995; Park et al 1994, 1997) and to 14.8 MBq in the mid-1990s (Mettler and Guiberteau 1998; Becker et al 1999; Kowalsky and Falen 2004; Balon et al 2006a; Joyce and Swihart 2011).…”