Iodine Radioisotope Diagnostic Scanning With SPECT/CT After Thyroidectomy for Thyroid Cancer: Essential Data or Unnecessary Investigation?

Abstract

In the clinical management of patients with differentiated thyroid cancer after total thyroidectomy, there is controversy on the utility of postsurgical iodine radioisotope diagnostic imaging (using 131-I or 123-I), with or without single photon emission computed tomography (SPECT)/ computed tomography (CT). Some arguments supporting the use of postsurgical radioactive iodine (RAI) diagnostic scans, with or without SPECT/CT, include beliefs that this procedure may optimize postoperative risk classification by ascertaining disease status/staging, optimize selection of patients with RAI-avid disease for RAI therapy, optimize RAI therapeutic dose activity selection, and identify patients who may benefit from additional surgical therapy (such as debulking of distant metastases or resection of a large thyroid remnant) (1). Theoretical challenges in endorsing routine use of postoperative RAI diagnostic scans, with or without SPECT, may include the lack of controlled trials proving that a strategy of using such scans to guide RAI treatment decisions (including patient selection for treatment or dose activity selection) improves long-term patient outcomes or reduces overall healthcare costs, compared to a strategy of therapeutic decision-making based on clinicopathological stage with additional cross-sectional imaging (such as preor postoperative neck ultrasound). Moreover, there are conflicting data on whether pretherapy 131-I diagnostic scans reduce efficacy of remnant ablation, with some authors reporting an adverse impact (2, 3) and others reporting no significant difference, as compared to empiric 131-I treatment (4). A pretherapy 131-I scan dose activity of 1 mCi (37 MBq) has been reported to be less likely to impair success of remnant ablation, compared to higher dose activities (5). A practical issue in considering the feasibility of postsurgical RAI diagnostic scanning in medical decision-making is the institutional ability/inability to modify preordered therapeutic dose activities of 131-I, in response to data obtained in the days preceding therapy. Clinical practice guideline recommendations on the use of postsurgical RAI diagnostic scanning are variable. The American Thyroid Association has recommended select use of postsurgical RAI diagnostic scanning or uptake measurement if the size of the thyroid remnant cannot be determined by other means or if the results would impact decision-making (on selection for RAI treatment or dose activity selection) (6). A European consensus panel provided a conditional recommendation for the use of postsurgical RAI diagnostic scanning if there is uncertainty about the extent of thyroidectomy (7). The British Thyroid Association suggested that preablation scanning is not routinely indicated but can be performed to assess remnant size if the extent of thyroidectomy is uncertain (8). The Society for Nuclear Medicine has indicated that “routine” preablation scanning “can be useful in guiding 131-I therapy” (9). The European Association for Nuclear Medicine has recommended that 131-I diagnostic scanning or uptakes should be avoided in cases where RAI therapy is clearly necessary because the results would not alter clinical management and the procedure may impair therapeutic efficacy (10). The Latin American Thyroid Association has acknowledged the controversy surrounding this procedure (11). In summary, there is some disagreement internationally on the utility of post-thyroidectomy RAI diagnostic scans.