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SU‐GG‐I‐05: CT‐Perfusion and FDG‐PET Imaging in Rectal Cancer: New Insights into Tumor Vasculature

Purpose The purpose of this study was to prospectively investigate tumor perfusion in rectal cancer and to determine early changes after hypofractionated radiotherapy. Furthermore, we correlated FDG uptake and tumor perfusion parameters intratumorally. Method and Materials Thirty patients diagnosed with rectal cancer were prospectively included in this study. All patients underwent FDG‐PET and perfusion‐CT imaging prior to the start of radiotherapy treatment. The perfusion‐CT images were analyzed using the extended Kety‐model, quantifying tumor perfusion with three parameters: K trans , v e and v p . On the PET‐images, the tumor was delineated using automated SUV‐thresholding with the threshold (percentage of SUVmax within the tumor) depending on the tumor‐to‐background signal ratio. For each patient and for several tumor subrogions, the mean and maximum FDG uptake (SUV) and tumor perfusion (K trans ) were quantified and correlated using the Spearman's rank correlation coefficient (ρ).Results The median tumors Ktrans values increased significantly after radiotherapy. Also, histogram analysis showed a shift of tumor voxels from lower Ktrans values towards higher Ktrans values. The median Ktrans values were significantly higher for tumor than for muscletissue on both the pre‐scan and the post‐scan. In contrast, no differences between tumor and muscletissues before and after radiotherapy were found for v e and v p . When correlating the tumors mean and maximum K trans values to the corresponding SUVs, positive correlations were found. Also when correlating the mean and maximum perfusion and FDG uptake within the created tumor subrogions, positive correlations were found. Conclusion Hypofractionated radiotherapy of rectal cancer leads to an increased tumor perfusion as reflected by an elevated Ktrans. FDG uptake was found to correlate with tumor perfusion assessed from dynamic perfusion‐CT images. Highly perfused rectal tumors presented with higher FDG uptake levels when compared to relatively low perfused tumors.