Prediction of treatment response to ¹³¹I therapy by diffuse hepatic uptake intensity on post-therapy whole-body scan in patients with distant metastases of differentiated thyroid cancer.

OBJECTIVE

A diffuse hepatic uptake (DHU) on radioiodine whole-body scans (WBS) after (131)I therapy is caused by (131)I-labeled iodoproteins, particularly (131)I-labeled thyroglobulin (Tg). We hypothesized that the DHU intensity after (131)I therapy might correlate with subsequent serum Tg reduction, suggesting that DHU reflects destruction of functioning thyroid tissue as measured by serum Tg.

MATERIALS AND METHODS

We retrospectively reviewed the medical records and (131)I WBSs of 47 patients treated with (131)I therapy for distant metastasis from differentiated thyroid cancer (M:F = 15:32, median age 45 years, range 11-74 years). All patients received post-ablative (131)I scans (PAWBS) at first (131)I ablation after total thyroidectomy and post-therapy (131)I scan (PTWBS) at second (131)I therapy. The DHU intensities of the PAWBS and PTWBS were classified into 3 grades: 1, faint; 2, modest; and 3, intense. Serum thyroid-stimulating hormone-stimulated Tg (sTg) levels were measured at the time of each therapy and 1 year after the second (131)I therapy.

RESULTS

One year after the second (131)I therapy, 10 patients (21.3%) were in remission and 37 (78.7%) had persistent disease. The DHU intensity on PAWBS correlated with the percentage sTg reduction at the next follow-up point (σ = 0.466, p = 0.0016). The patients with intense DHU on PTWBS tended to have a higher percentage sTg reduction than the other patients, although statistical significances were marginal (Spearman's rank correlation: σ = 0.304, p = 0.054; Kruskal-Wallis test: p = 0.067). In univariate analysis, the DHU grades on PAWBS and the initial sTg levels were significantly different between patients in remission and those with persistent disease (PAWBS: p = 0.022; initial sTg: p = 0.0059). In multivariate logistic regression analysis, after adjusting for initial sTg levels, a DHU grade of 3 on PAWBS was an independent predictor of remission (PAWBS: p = 0.028; initial sTg <100 ng/ml: p = 0.043).

CONCLUSIONS

In patients with iodine-avid distant metastases, intensity of DHU on (131)I post-therapy scan correlated with subsequent percentage serum sTg reduction. Also, intense DHU could be one of the predictors of remission in these patients.