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A Correction of Partial Volume Effect for Using PET to Define Metabolically Active Tumor Volume for Pancreatic Cancer

E Dalah*, Y Cungeng, I Moraru, B Erickson, X Li, Medical College of Wisconsin, Milwaukee, WI

SU-D-500-3 Sunday 2:05PM - 3:00PM Room: 500 Ballroom

Purpose: Accurate delineation of tumor volume based on PET is affected by partial volume effect (PVE) that has been shown to result in underestimations of the standardized uptake value (SUV), leading to decreased metabolically-active tumor volume (MATV). Here we assess the impact of a PVE correction on the SUV and the PET defined MATV in patients with pancreatic cancer.

Methods:A voxel-by-voxel PVE correction method utilizing a recovery coefficient (RC) approach is implemented for correction in the region of interest (ROI). A profile-analysis study was used to define the ideal-cutoff-values (IDCVs) to threshold PET. The RC and the IDCVs were calculated using NEMA phantom. The pancreas tumor volumes were delineated on the T1 with contrast and diffusion-weighted MRI (DWI), and on the PET using four different cutoff values: 2.5-SUV, tumor-to-background (T/B) ratio, 42% of SUVmax, and IDCVs. The PVE-corrected PET and MATV were compared with the original PET, and the resulted tumor sizes were compared with those from contrast-enhanced CT and MRI.

Results:For all patients studied, the mean RC was 0.72 (ranging 0.58 - 0.81) based on tumor diameter on the CT (ranging 1.9 - 5.8) cm, and tumor-to-background ratio (ranging 2.4 - 8.7). The mean SUVmax values in the ROI were 8.2 (ranging 3.9 - 13.1) and 10.6 (ranging 5.57 - 16.37) g/ml, respectively, before and after PVE correction. Generally, all of the 2.5-SUV, T/B ratio, and 42% SUVmax showed an increase of up to 34% in the MATV after PVE correction except for the IDCVs MATV was reduced by 21%. The differences between tumor sizes from CT, T1, and DWI and those from PET with PVE-correction were reduced compared to those without correction.

Conclusion:The partial volume effect correction considerably impacts PET SUV and improves the PET-defined metabolic₋ally-active tumor volume, particularly for small pancreatic tumors.

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