High Concordance Rate on SSTR-RADS Version 1.0 As a Reporting System for SSTR PET Imaging and Selection of Potential PRRT Candidates

363 Objectives: Recently, a standardized framework system for interpreting somatostatin receptor (SSTR)-targeted PET/CTs, termed SSTR-Reporting and Data System (RADS) 1.0, has been introduced providing reliable standards and criteria for SSTR PET. We determined the interobserver reliability of SSTR-RADS for interpretation of 68Ga-DOTATOC PET/CT scans in a multicentric, randomized setting. Methods: A set of 51 randomized 68Ga-DOTATOC PET/CT scans was independently assessed by four blinded readers with different levels of experience (2 experienced readers (ER) and 2 inexperienced readers (IR)) trained with SSTR-RADS 1.0 criteria (based on a 5-point scale (from 1 = definitively benign to 5 = high certainty that neuroendocrine tumor is present)). Per scan, SSTR-RADS scores were assigned to a maximum of 5 target lesions (TL). An overall scan impression based on SSTR-RADS was indicated, and interobserver agreement rates on a TL-based, on an organ-based, and on an overall SSTR-RADS score-based level were computed. Readers were also asked to indicate whether peptide receptor radionuclide therapy (PRRT) should be considered based on the assigned RADS scores. Results: Among the selected TL, 153 were chosen by at least 2 individual observers (all 4 readers selected the same target lesion in 58 of 153 [37.9%] instances). The interobserver agreement for SSTR-RADS scoring among identical TL was good (intraclass correlation coefficient [ICC] for 4, 3, and 2 identical target lesions, ≥0.73, respectively). For lymph node and liver lesions, excellent interobserver agreement rates were derived (ICC, 0.91 and 0.77, respectively). Moreover, the interobserver agreement for an overall scan impression based on SSTR-RADS was excellent (ICC, 0.88). Decision for PRRT based on SSTR-RADS demonstrated an excellent agreement with an ICC of 0.8. No significant differences between ER and IR for overall scan impression and TL-based analyses were observed (p≥0.18, respectively), thereby suggesting that SSTR-RADS seems to be readily applicable even for less experienced readers. Conclusions: SSTR-RADS criteria demonstrated a high concordance rate, even among readers with different experience, supporting the adoption of SSTR-RADS for trials, or clinical routine. Further increase in interobserver reliability could be derived by stricter advice on selecting TL.