The Ratio of Lymph Node to Primary Tumor SUV on PET/CT Accurately Predicts Nodal Malignancy in Non- Small Cell Lung Cancer Malcolm Mattes, Salma Ahsanuddin, Aditya Apte, Ariella Moshchinsky, Nabil Rizk, Amanda Foster, Abraham Wu, Hani Ashamalla, Joseph Deasy, Wolfgang Weber, Andreas Rimner Department of Radiation Oncology, Memorial Sloan- Kettering Cancer Center, New York, NY, USA

Background/Methods The goal of this study was to determine whether using the ratio of the lymph node to primary tumor SUVmax (SUV N/T ) may be a better predictor of nodal involvement with malignancy than absolute SUV max alone. Included 175 patients with 504 LNs that were both biopsied and visualized on a PET/CT within 31 days prior to biopsy. SUV Ratio Predicts NSCLC Nodal Pathology

Results The optimal cutoff value of SUV N/T to predict nodal involvement with malignancy was 0.27 – Sensitivity 93%, specificity 87% Sensitivity was >95% at SUV N/T < 0.17 Specificity was >95% at SUV N/T > 0.44 For all evaluated LNs, there was no significant difference between SUV N/T & SUV max SUV Ratio Predicts NSCLC Nodal Pathology

Results Among patients with hypermetabolic primary tumors (SUV max > 2.5), SUV N/T was even more accurate than SUV max in assessing lymph nodes with a mild to intermediate elevation in SUV max (2.0 – 6.0) SUV Ratio Predicts NSCLC Nodal Pathology

Conclusion This N/T ratio has the potential to serve as an important adjunct PET/CT parameter to improve: – non-invasive nodal staging – radiotherapy treatment planning Other tumor characteristics like primary size, histology, nodal size, and nodal distribution as well as technical factors like the partial volume effect, respiratory motion signal degradation, and scanner specific parameters may still need to be taken into account in interpreting nodal involvement with malignancy. SUV Ratio Predicts NSCLC Nodal Pathology