Significance of a single time point hybrid-protocol for somatostatin receptor SPECT including multiphase CT in the diagnostic work-up of gastroenteoropancreatic neuroendocrine Neoplasms (GEP-NEN)

Aim: This prospective study compared a one-day hybrid-SPECT/CT protocol (incl. multiphase CT-scans) to the commonly used three-day protocol for somatostatin receptor scintigraphy (SRS) in patients suffering from gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN). Additionally, the SPECT/CT-influence on patient management was evaluated. Methods: From 10/2011 to 10/2012 all GEP-NEN-patients undergoing restaging with SRS with a modern SPECT/CT-device SPECT/CT (Discovery NM/CT670, GE) were enrolled in this study. The examination-protocol consisted of planar scanning 4, 24 and 48 h p.i., whole-body low-dose SPECT/CT-imaging at 24 and 48 h (SPECT-ldCT24, SPECT-ldCT48) and diagnostic multiphase CT (dCT24) at 24 h coregistered to the corresponding SPECT (SPECT-ldCT24). All imaging data-components were reassessed by three blinded readers (R1, R2, R3). The results were compared to a reference standard (RS) based on all clinical, imaging and histopathology follow-up data available (24-36, mean 29.9 months). RS was defined by a study-specific interdisciplinary tumor board (SITB) that also reassessed treatment decisions. Results: 31 patients (m, n = 18; f, n = 13; mean age, 60.4 years) were eligible for analysis. 10/31 patients had no imaging sign of disease and remained disease-free during follow-up. 21/31 patients had persistent/recurrent disease (n = 82 lesions: liver n = 24; lymph-node n = 21; bone n = 16; pancreas n = 12; others n = 9). A lesional detection rate of 51.9%(R1), 49.4%(R2) and 71.6%(R3) for SPECT-ldCT24, 51.9%(R1), 55.6%(R2) and 67.9%(R3) for SPECT-ldCT48 and 63.0%(R1), 70.4%(R2) and 85.2%(R3) for dCT24 was observed, respectively. SPECT-dCT24 yielded the highest detection rate with 77.8%(R1), 84.0%(R2) and 88.9%(R3), respectively. Interobserver agreement was moderate for SPECT-dCT24 (=0.44), dCT24 (=0.43), SPECT-ldCT48 (=0.61) and for SPECT-ldCT24 (=0.55). For planar scans it was fair after 48 h (=0.36) and 24 h (=0.38), respectively, and moderate after 4 h (=0.42). Every lesion present in planar or SPECT-ldCT-imaging was also detectable in SPECT-dCT24, which also showed a great complementarity, as 34/82 (41.4%) lesions were detected by a single submodality only. Integrated SPECT/CT reading influenced therapeutic management in 8/31 (25.8%) patients. Conclusion: The highest detection rates are achieved by SPECT-dCT24. Thus, a more patient-friendly one-day-examination protocol is feasible. Furthermore, the multiphase hybrid-SPECT/CT-examination impacted on patient management in about one fourth of all patients.

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