Association between Refractoriness to 131I Therapy for Differentiated Thyroid Carcinoma and 18F-FDG Accumulation in Lung Metastasis

Background: The purpose of this study was to retrospectively investigate the association between 2-[F-18]-fluoro-2-deoxy-D-glucose (18F-FDG) accumulation in lung metastasis (LM) before 131I therapy and refractoriness to 131I therapy for differentiated thyroid carcinoma (DTC) patients.

Methods and Findings: Sixty-one DTC patients with LM who underwent Positron emission tomography/computed tomography using 18F-FDG (18F-FDG PET/ CT) before an initial 131I therapy were retrospectively evaluated. Maximum of standardized uptake value (SUVmax) in LM with the highest 18F-FDG accumulation was measured in each patient. The SUVmax was compared between patients with and without 131I-positive LM, and between patients with and without an increased level of thyroglobulin (tumor marker) 12 ± 2 months after 131I therapy using the Wilcoxon test.

Discussion: Predictability for the patients with an increased thyroglobulin level was also analyzed by receiver-operating-characteristic (ROC) analysis. SUVmax of LM was significantly greater for patients without 131I-positive LM than for those with 131I-positive LM (5.9 ± 6.0 vs. 1.9 ± 2.0, p<0.01) and was significantly greater for patients with an increased level of TG after 131I therapy than for those without (7.0 ± 4.9 vs. 1.2 ± 1.0, p<0.01). All 11 of the 49 patients with SUVmax > 3.8 showed an increased TG level after 131I therapy. Use of the optimal cutoff threshold for SUVmax of 1.6 differentiated patients with an increased level of TG from those without at a sensitivity of 74.2%, a specificity of 94.4%, an accuracy of 81.6% and an AUC of 0.91.

Conclusion: 18F-FDG accumulation in LM from DTC can be one of predictors for refractoriness to 131I therapy.


Yasuhiro Maruoka, Shingo Baba, Takuro Isoda, Yoshiyuki Kitamura, Koichiro Abe, Masayuki Sasaki and Hiroshi Honda

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