Interreader and Intrareader Reproducibility of ¹⁸F-Flotufolastat Image Interpretation in Patients with Newly Diagnosed or Recurrent Prostate Cancer: Data from Two Phase 3 Prospective Multicenter Studies

Interreader and intrareader reproducibility of ¹⁸F-flotufolastat PET/CT scans in newly diagnosed and recurrent prostate cancer patients was assessed from masked image evaluations from two phase 3 studies. Methods: ¹⁸F-flotufolastat PET/CT images of newly diagnosed (n 5 352) or recurrent (n 5 389) patients were evaluated by 3 masked readers. Cohen k was used to assess pairwise patient- and region-level interreader agreement. Agreement among all readers was assessed using Fleiss k. Intrareader agreement between the first and repeat read (20% of images, $4 wk later) was assessed using Cohen k. Results: Pairwise interreader agreement was 95% or better (newly diagnosed) and 75% or better (recurrent). The k coefficients were impacted by the high-agreement–low-k paradox: Cohen k ranged from not estimable to 0.55, whereas Fleiss k was 0.50 (newly diagnosed) and 0.41 (recurrent). Agreement was highest in the prostate of newly diagnosed patients ($95%) and in the pelvic lymph nodes in recurrent patients ($87%). Intrareader agreement was 86% or better across both populations. Conclusion: ¹⁸F-flotufolastat PET/CT images can be reliably interpreted, with a high degree of inter- and intrareader agreement.