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

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

We retrospectively reviewed the medical records and ¹³¹I WBSs of 47 patients treated with ¹³¹I 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 ¹³¹I scans (PAWBS) at first ¹³¹I ablation after total thyroidectomy and post-therapy ¹³¹I scan (PTWBS) at second ¹³¹I 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 ¹³¹I therapy.

One year after the second ¹³¹I 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).

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