Abstract
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. PTV<sub>CT</sub>-based plans were initially made, and then PTV<sub>PET-CT</sub>-based plans were created using the same beam angles and isocenter. The dosimetric parameters analyzed included GTV<sub>CT</sub>, PTV<sub>CT</sub>, GTV<sub>PET-CT</sub> and PTV<sub>PET-CT</sub>. 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<sub>PET</sub>/GTV<sub>CT</sub> mismatch was 49.5 ± 28.9%, and that for GTV<sub>CT</sub>/GTV<sub>PET</sub> was 95.9 ± 19.5%. The mean value for PTV<sub>PET-CT</sub>/PTV<sub>CT</sub> mismatch was 21.9 ± 7.0% and that for PTV<sub>CT</sub>/PTV<sub>PET-CT</sub> 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.
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