Negative remnant ^99mTc-pertechnetate uptake predicts excellent response to radioactive iodine therapy in low- to intermediate-risk differentiated thyroid cancer patients who have undergone total thyroidectomy

Objective

Negative ^99mTc-pertechnetate uptake of the thyroid bed indicates the absence or a small volume of remnant thyroid tissue (RTT) after total thyroidectomy (TT). The aim of this study is to evaluate the predictive value of negative ^99mTc-pertechnetate scintigraphy for excellent response (ER) to radioactive iodine therapy (RIT) in low- to intermediate-risk differentiated thyroid cancer (DTC) patients.

Patients

One-hundred and eighty-nine low- to intermediate-risk DTC patients who underwent TT, RIT with a single dose of 30 mCi and suppressive therapy with thyroid-stimulating hormone (TSH) from July 2015 to February 2016 in our hospital were retrospectively evaluated. ^99mTc-pertechnetate thyroid scintigraphy was performed just before RIT and images were reported dichotomously as negative or positive. The response of patients was assessed for 23.2 ± 3.8 months after RIT and dichotomized as excellent response (ER) or non-excellent response (NER). ^99mTc-pertechnetate uptake, age at diagnosis, gender, multifocality, T stage, N stage, preablative stimulated thyroglobulin (ps-Tg), and TSH were explored as potential predictors for ER.

Results

80.68% (71/88) of patients with negative ^99mTc-pertechnetate uptake achieved ER. When patients were evaluated according to different ps-Tg levels, we found that 94.83% (55/58) of patients with ps-Tg < 1 ng/ml and negative ^99mTc-pertechnetate uptake achieved ER. Multivariate Cox regression analysis revealed that ps-Tg (P = 0.0001) and ^99mTc-pertechnetate uptake (P = 0.0473) were independent predictors for ER.

Conclusions

In addition to ps-Tg, negative ^99mTc-pertechnetate uptake is also a significant independent predictor for an excellent response in low- to intermediate-risk patients. It may be possible to omit RIT in patients with ps-Tg < 1 ng/ml and concurrent negative ^99mTc-pertechnetate uptake.