CT radiomic analysis using lymph-node-density profile in correlation to SUV-value for PET/CT based N-Staging

In patients with lung cancer (LC), malignant melanoma (MM), gastroenteropancreatic neuroendocrine tumours (GEP-NETs) and prostate cancer (PCA), N-staging is often performed by integrated (18)F-FDG-Positron Emission Tomography/Computed Tomography (PET/CT) (LC, MM), (68)Ga-DOTATOC-PET/CT (GEP-NET) and (68)Ga-PSMA-PET/CT (PCA): N-staging is not always accurate due to indeterminate PET-findings. To better evaluate malignant lymph node (LN) infiltration, additional surrogate parameters, especially in cases with indeterminate PET-findings, would be helpful. The purpose of this study was to evaluate if maximal standardized uptake values (SUVmax) in the PET-examination might correlate with semi-automated density measurements of LN in the CT-component of the integrated PET/CT examination.

After approval by the institutional review board, 1022 LNs in PET/CT-examinations of 148 patients were retrospectively analysed (LC: 327 LN out of 40 patients, MM: 224 LN out of 33 patients; GEP-NET: 217 LN out of 35 patients, PCA: 254 LN out of 40 patients). PET/CT was performed before surgery/biopsy, chemotherapy, or internal or external radiation therapy, according to the clinical schedule, patients with prior chemotherapy or radiation therapy were ruled out. LN analyses were performed on the basis of SUV-uptake 60 minutes after tracer injection and volumetric CT histogram analysis in non-contrast enhanced CT.

LNs were considered positive or negative on the basis of tracer uptake, histological confirmation was not available. Of the 1022 lymph nodes, 331 had positive SUVmax-findings (3-times SUVmax of bloodpool), 86 were indeterminate (1-3 SUVmax bloodpool), 605 were negative (< SUVmax bloodpool). LNs with positive SUV-uptake had significantly higher CT-density values compared to PET-negative LN, irrespective of the cancer entity.

Density measurements of LNs in patients with LC, MM, GEP-NET and PCA correlate with FDG uptake in PET, and might therefore serve as an additional surrogate parameter for the differentiation between malignant and benign LNs. A possible density threshold in clinical routine might be a 7.5 Hounsfield Units (HU) cut-off value to differentiate between malignant and benign LN infiltration, and a 20 HU cut off to exlude benign lymph node processes, especially helpful in PET-indeterminate LNs.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2016 Sep 22 [Epub ahead of print]

Frederik Giesel, Florian Schneider, Clemens Kratochwil, Daniel Rath, Tim Holland-Letz, Jan Moltz, Hans-Ulrich Kauczor, Lawrence Schwartz, Uwe Haberkorn, Paul Flechsig

University Hospital Heidelberg, Germany;, Core Facility of Statistics, German Cancer Research Center, Heidelberg;, Fraunhofer MEVIS, Institute for Medical Image Computing, Bremen;, Columbia, United States.