TY - JOUR T1 - The quest for an accurate functional tumor volume with <sup>68</sup>Ga-DOTATATE PET/CT JF - Journal of Nuclear Medicine JO - J Nucl Med DO - 10.2967/jnumed.121.262782 SP - jnumed.121.262782 AU - Ryan P Reddy AU - C Ross Schmidtlein AU - Romina G Giancipoli AU - Audre Mauguen AU - Daniel LaFontaine AU - Heiko Schoder AU - Lisa Bodei Y1 - 2021/11/01 UR - http://jnm.snmjournals.org/content/early/2021/11/11/jnumed.121.262782.abstract N2 - Rationale: 68Ga-labelled somatostatin analog PET/CT (SSA PET/CT) is now standard of care component in management of neuroendocrine tumors (NETs). However, treatment response for NETs is still performed with morphologic size measurements from other modalities, which can result in inaccurate disease burden. Functional tumor volume (FTV) acquired from SSA PET/CT has been suggested as a possible metric, but no validated measurement tool to measure FTV exists. We tested the precision of multiple FTV computational approaches compared to morphologic volume measurements to identify a candidate for incorporation into future FTV studies to assess tumor burden more completely and accurately. Methods: The clinical and imaging data of 327 NET patients was collected at MSKCC between December 2016 and April 2018. Patients were required to have SSA PET/CT and dedicated CT scans within 6 weeks. and were excluded if they had intervention between scans. When paired studies were evaluated, 150 correlating lesions demonstrated somatostatin analog. Lesions were excluded if they contained necrotic components or demonstrated a lobulated shape. This resulted in 94 lesions in twenty patients. The FTV for each lesion was evaluated with a hand-drawn assessment and three automated techniques – a 50% threshold from SUVmax, 42% threshold from SUVmax, and background-subtracted lesion histogram-based (BSL) method. These measurements were compared to volume calculated from morphologic volume measurements. Results: The FTV calculation methods demonstrated varying amount of correlation to morphologic volume measurements. FTV using threshold of 42% of SUVmax with 0.706 correlation, hand-drawn volume from PET imaging with 0.657 correlation, FTV using threshold of 50% of SUVmax with 0.645 correlation, and BSL method with 0.596 correlation. The Bland-Altman plots indicates that all FTV methods have positive mean difference compared to morphological volume, with FTV from threshold of 50% relative to SUVmax demonstrating the smallest mean difference. Conclusion: FTV determined with thresholding of SUVmax demonstrated the strongest correlation with traditional morphologic lesion volume assessment and the least bias. This method outperformed FTV calculated from hand drawn volume assessments with regards to accuracy. Automated FTV assessment based on a threshold shows promise to better determine extent of disease and make better prognostic assessments for patients with NETs. ER -