Role of Tc-99m pertechnetate for remnant scintigraphy post-thyroidectomy

Current surgical techniques in patients with differentiated thyroid cancer can leave little or no remnant tissue. Coupled with favorable prognostic factors, this subgroup of patients might not require radioablative remnant ablation with Iodine-131 (I-131). Postoperative scanning may help to identify this subgroup, however low dose I-131 can lead to stunning and suboptimal response to ablative therapy. Iodine-123 (I-123) can be used but is expensive and supply can be limited. We investigate technetium-99m pertechnetate (pertechnetate) as a potential alternative for remnant scintigraphy post-thyroidectomy.

Seventy consecutive post-total-thyroidectomy patients were evaluated retrospectively. Preablative pertechnetate scans of the thyroid bed were viewed blindly then directly compared with postablative I-131 scans.

For patients with unequivocally positive pertechnetate uptake, the sensitivity was 81% (patients), 61% (sites), and the PPV was high (100% patients, 95% sites). In patients with either definite or equivocal pertechnetate uptake, the sensitivity was 90% (patients), 68% (sites), and the PPV was also high (100% patients, 81% sites).

Pertechnetate had reasonable correlation with postablative I-131 scans with a moderately high sensitivity and a very high PPV. A positive pertechnetate scan is therefore sufficient to guide progression to I-131 ablation in most patients. When the scan is equivocal or negative, diagnostic imaging with radioiodine may be required. Pertechnetate scintigraphy may be of particular benefit if it is considered desirable to avoid I-131 in post-thyroidectomy remnant imaging.