FDG PET/CT predicts extrahepatic metastatic potential for treatment planning and endpoint of liver directed yttrium-90 microsphere therapy of colorectal metastasis

Objectives To assess the extrahepatic metastatic (Met) potential before intra-arterial Y-90 microsphere treatment (Tx) of colorectal (CRC) liver Mets and determine the Tx endpoint of tumor load reduction.

Methods 27 patients (pt) with CRC Mets to the liver and F-18 FDG PET scans were included. All pts had also baseline CT, hepatic angiography, and intra-arterial Tc-99m MAA scans. Pre-Tx PET images were analyzed by visual inspection of extrahepatic Mets (EHM) and by computer quantification of total liver tumor metabolism. For each pt, ROIs were drawn along the liver edge to measure total liver standard uptake value (TL-SUV) on axial images, covering the entire span of the liver. The TL-SUV was then converted by logarithm for comparison by t-tests for EHM. ROC and discriminant analysis was used to determine Tx endpoint.

Results There were 9 and 18 pts identified to be negative and positive for EHM. The natural logarithms of TL-SUV of the group with negative EHM was significantly lower than that with positive EHM (9.08+/-0.25 vs 9.58+/-0.65, p=0.008) with a 100% specificity cut-off at 9.45.

Conclusions There is significant difference in liver tumor load regarding the presence or absence of EHM. This identifies a total liver SUV threshold, below which EHM are unlikely and provides guidance to generate an SUV cut-off value that could become the intermediate PET endpoint of tumor load reduction after Y-90 Tx.