Comparison of computed tomography- and positron emission tomography-based radiotherapy planning in cholangiocarcinoma.

Introduction: The aim of this study was to compare computed tomography (CT)- and positron emission tomography (PET)/CT-based gross tumor volume (GTV) delineation and its subsequent expansion to the planning target volume (PTV), and to analyze the resultant doses of 3-dimensional conformal radiotherapy (3D-CRT) to critical organs. Methods: 15 patients with unresectable extrahepatic cholangiocarcinoma (EHCC) were enrolled into this study. PTVCT-based plans were initially made, and then PTVPET-CT-based plans were created using the same beam angles and isocenter. The dosimetric parameters analyzed included GTV(CT), PTVCT, GTV(PET-CT) and PTVPET-CT. Prescribed and delivered radiation doses to target volumes and delineated organs at risk were also compared. Results: Mean GTV and PTV were significantly reduced in the PET/CT-based plan compared to the CT-based plan; the mean reductions of GTV and PTV were 28.7% and 15.2%, respectively. The mean value for GTV(PET)/GTV(CT) mismatch was 49.5 +/- 28.9%, and that for GTV(CT)/GTV(PET) was 95.9 +/- 19.5%. The mean value for PTVPET-CT/PTVCT mismatch was 21.9 +/- 7.0% and that for PTVCT/PTVPET-CT was 39.1 +/- 9.2%. Liver doses were significantly reduced (17.1%) in the PET/CT-based plan compared to the CT-based plan; the doses received by at least 30% and 50% of the liver were 30.0%, and 27.3%, respectively. Conclusion: The potential benefit of PET/CT is the reduction in geographic misses and regional treatment failures associated with CT-based planning.