Clinical usefulness of I-131 SPECT/CT system for evaluating iodine uptake outside the neck in patients with differentiated thyroid cancer

Objectives We evaluated the diagnostic impact provided by I-131 SPECT/CT in terms of the precise characterization of iodine uptake outside of neck in patients with differentiated thyroid cancer (DTC).

Methods Among 326 patients who had undergone I-131 whole body scan after radioiodine therapy (RITx), 58 lesions in 49 patients presenting iodine uptake outside the neck were studied with a I-131 SPECT/CT. We categorized the 58 iodine uptakes outside of the neck on the planar image into equivocal and definitive metastatic lesion. Then they were recategorized into definitively benign, equivocal and definitively metastatic lesion on the subsequently acquired SPECT/CT image.

Results Total 6 lesions of 58 iodine uptakes on the outside of the neck were considered as metastases on the planar image and reaffirmed by I-131 SPECT/CT. Among the rest of the equivocal 52 lesions, 39 lesions (75%) were confidently diagnosed as benign uptake, 9 lesions (17%) were metastases and 4 lesions (8%) still remained equivocal. The benign lesions were orderly in gastrointestinal tract, breast, thymus, uterus, ovary and the metastatic lesions were predominantly in bone and lung. Total 48/52 (92%) equivocal lesions on the planar image were precisely characterized by the I-131 SPECT/CT. Overall, integrated I-131 SPECT/CT imaging changed the management of patients with RITx in 41/326 (13%).

Conclusions Integrated I-131 SPECT/CT system has diagnostic value over planar imaging for the precise characterization of equivocal iodine uptake on the outside of the neck and also has an impact on the management of patients with DTC.