Observer agreement and accuracy of ¹⁸F-sodium-fluoride PET/CT in the diagnosis of bone metastases in prostate cancer

Abstract

Aim: To evaluate the interobserver agreement in ¹⁸F-sodium fluoride (NaF) PET/CT for the detection of bone metastases in patients with prostate cancer (PCa). Materials and Methods:NaF PET/CT scans were retrieved from all patients who participated in four recent prospective trials. Two experienced observers independently evaluated the NaF PET/CTs on a patient level using a three-category scale (no bone metastases [M0], equivocal for bone metastases, and bone metastases present [M1]) and on a dichotomous scale (M0/M1). In patients with no more than 10 lesions, the location and number of lesions were recorded. On a patient level, the diagnostic performance was calculated using a sensitivity analysis, where equivocal lesions were handled as M0 as well as M1. Results: NaF PET/CTs from 219 patients with PCa were included, of whom 129 patients were scanned for primary staging, 67 patients for biochemical recurrence, and 23 patients for metastatic castration-resistant PCa. Agreement between the observers was almost perfect on a patient level (three-category scale unweighted κ: 0.83 ± 0.05, linear weighted κ: 0.90 ± 0.06; dichotomous scale κ: 0.91 ± 0.07). On a lesion level (dichotomous scale), the observers agreed on the number as well as the location of bone metastases in 205 (93.6%) patients. In the remaining 14 patients, the readers disagreed on the number of lesions in 13 patients and the location of bone metastases in one patient. A final diagnosis of bone metastases was made in 211 of 219 patients. The sensitivity ranged from 0.86-0.92, specificity from 0.83-0.97, positive predictive value from 0.70-0.93, and negative predictive value from 0.94-0.96. Conclusion: The interobserver agreement of NaF PET/CT for the detection of bone metastases in patients with PCa was very high among trained observers, both on a patient level and on a lesion level. Moreover, the diagnostic performance of NaF PET/CT was satisfactory, rendering NaF PET/CT a robust tool in the diagnostic armamentarium.