The value of additional ¹³¹I SPECT/CT in characterizing inconclusive uptakes distant from the neck on post-therapeutic planar whole-body scintigraphy at the first radioablation in patients with differentiated thyroid cancer

Objectives Posttherapeutic ¹³¹I planar whole body scintigraphy (ptWBS) plays a significant role in judging the therapeutic effectiveness and staging. However, it has some limitations of the lack of anatomical landmarks and false positive findings concentrating radioiodine. The purpose of this study was to evaluate the value of additional SPECT/CT in the characterization of inconclusive uptakes distant from the neck on ptWBS at the first radioablation therapy (RAIT) in patients with differentiated thyroid carcinoma (DTC).

Methods In this study, a total of 57 DTC patients (36 females, 21 males) who underwent SPECT/CT from January 2008 to July 2010 after the first RAIT due to inconclusive uptakes on ptWBS were analyzed. The data were evaluated on a lesion basis. SPECT/CT classified them as positive, negative, or equivocal. Final diagnoses were based on imaging modalities, serologic tests, or histopatholgic findings, and clinical follow-up which lasted one or more years.

Results SPECT/CT detected a total of 101 uptakes in 57 patients. By comparing with final diagnoses, this study found that the accuracy rate of SPECT/CT characterization stands at 79.0%: 64 in 81 lesions. Twenty four in 41 positive lesions were confirmed to be malignant and 40 negative lesions were all found to be benign. Only one false positive case was detected in the lung and it was later confirmed as a chronic inflammatory nodule.

Conclusions Additional ¹³¹I SPECT/CT seems to be effective in differentiating benign from malignant lesions for inconclusive uptakes on ptWBS after the first RAIT. In addition, it may reduce the need of other conventional imaging modalities.

Research Support Thyroid carcinoma; SPECT/CT; ¹³¹I; Whole body scintigraph