The FUSION iENA Study: Comparison of I-124-PET/US Fusion Imaging with Conventional Diagnostics for the Functional Assessment of Thyroid Nodules by Multiple Observers

Aim To investigate the value of I-124 positron emission tomography (PET) / ultrasound (US) fusion imaging in comparison to conventional diagnostics (CD) of Thyroid nodules (TN) by multiple observers. Methods Digital patient case files (PCF) of patients that received CD and I-124-PET/US in clinical routine were prepared containing cine-loops of the examinations. All physicians with nuclear medicine specialty from Germany, Austria, and Switzerland were invited to participate. 106 acquired observers completed 7.2 +/- 1.8 (median: 8, range: 4-14) randomly assigned PCF (CD only or CD+PET/US). They assessed the TN function, stated their confidence in functional assessment, and suggested a treatment course for each TN. Results 68 PCF of 34 patients comprising 66 TN >= 1 cm (= 1.94 TN/patient) were created. A total of 748 (11.2/TN), and 751 ratings (11.4/TN) were recorded for CD only, and CD+PET/US, respectively. The functional assessment revealed more hyper- or hypofunctioning (524 vs. 320, p < 0.0001) and less indifferent or not rateable (209 vs. 428, p < 0.0001) TN in CD+PET/US vs. CD only. The observers' confidence in functional assessment was superior in CD+PET/US (p < 0.0001). Furthermore, the ratings were carried out more homogeneous in CD+PET/US (p < 0.0001). Fewer suggestion of follow up (p < 0.0001), and more (p < 0.0001) suggestion of invasive treatments (fine-needle aspiration & surgery) was observed in CD+PET/US. Radioiodine therapy was more often (p = 0.0036), and thyroid medication less often (p = 0.0167) advised in CD+PET/US. Conclusion Functional assessment of equivocal TN shows frequent failures in CD, underestimating the incidence of hyper- and hypofunctioning lesions. Confidence in functional assessment significantly increases with additional PET/US. This influences the proposed treatment course.