POST-THERAPY IMAGING AFTER RADIOACTIVE IODINE THERAPY FOR DIFFERENTIATED THYROID CANCER: THE CONTRIBUTION OF SPECT-CT IMAGING TO PLANAR IMAGING

Objective: The aim of this study was to investigate the contribution of SPECT-CT to planar imaging in patients with differentiated thyroid carcinoma (DTC) following radioiodine therapy. Materials and Methods: Post-therapy scan was performed on 325 patients (254 women, 71 men; age range 15-81 years) who were operated on for DTC and treated with radioactive iodine (100-200 mCi) therapy. Whole-body planar imaging and neck- chest planar + SPECT-CT imaging were performed on all patients. Additional SPECT-CT scans were performed in other areas where suspicious findings were observed on the planar images. The iodine-positive areas on the planar images were classified as benign, equivocal, or malignant and were also reevaluated by two nuclear medicine physicians using SPECT-CT images. The final diagnosis was verified by histology, other imaging modalities, and clinical-serological follow-up. Results: Based on patient-based analysis, SPECT/CT altered the interpretation of the planar scans by detecting the following findings: additional metastatic lymph nodes in 21 (21/50) patients, lung metastases in 2 (2/10) patients, and bone metastases in 2 (2/12) patients. Furthermore, SPECT/CT confirmed that equivocal focal uptakes were benign in 83 patients and malign in 48 patients. The sensivity, specificity, positive predictive value, negative predictive value, and accuracy were 63.4%, 92.7%, 67.7%, 91.3%, and 87%, respectively, for the planar imaging and 96.8%, 100%, 100%, 99.2%, and 99.3%, respectively, for the SPECT-CT imaging. Overall, SPECT-CT affected therapy management in 76 patients (23.3%). Conclusion: SPECT-CT imaging improves diagnostic accuracy by reducing false-negative or -positive results in planar imaging in the post-therapy scan in patients with DTC. Our findings suggest that neck-thorax SPECT-CT imaging should be incorporated into the routine imaging protocol for detecting the most metastatic sites of DTC.