DOSIMETRIC COMPARISON OF THREE-DIMENSIONAL CONFORMAL RADIATION THERAPY (3D-CRT), INTENSITY MODULATED RADIATION THERAPY (IMRT) AND VOLUMETRIC MODULATED ARC THERAPY (VMAT) FOR DISTAL ESOPHAGEAL CANCER TREATED WITH EXTERNAL RADIATION

Abstract

Purpose/Objectives: Intensity Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) provide advantages in delivery of radiation allowing conformality of delivered dose to the planning target and reducing dose to organs at risk (OAR), however, at the potential cost of low dose spread. Due to the central location of the esophagus and GE junction, dose to lungs, heart, spinal cord, liver, and kidneys must be considered. Low dose spread is of particular concern with respect to healthy lung tissue. This study comprehensively compares volumetric dose statistics of the standard three-dimensional conformal radiation therapy (3D-CRT) compared with VMAT and IMRT for distal esophageal cancer treatment. Materials/Methods: Forty patients who underwent pre-operative radiation therapy for esophageal cancer between 2012-2014 were retrieved from our database. Pinnacle planning software was used to create 3D-CRT, VMAT and IMRT radiation plans for all patients. Forty-five (45) Gy was prescribed for each patient with D95% > 42.75Gy for the planning target volume (PTV). All plans were optimized to maintain PTV coverage while reducing dose to OAR with specific emphasis on lung and heart dose. Volumetric dose statistics were obtained, and Wilcoxon signed rank test was used to compare 3D-CRT vs IMRT and VMAT for Conformity Index, Integral Dose, Monitor Units, lung (V5Gy, V20Gy, mean, max), heart (V30Gy, mean, max), spinal cord max, bilateral kidneys (V20Gy, mean) and liver mean dose. Comparison was also made for IMRT vs VMAT. Results: For both IMRT and VMAT compared with 3D-CRT, statistically significant pairwise differences were noted for Conformity Index (-28.51%, -30.70%, P<.001), Integral Dose (-14.0%, -14.8%, P<.001), Monitor Units (107.2%, 80.4%, P<.001), lung (V20Gy: -49.7%,-57.4%, mean: -20.3%,-24.9%, P <.001), heart (V30Gy : -10.1%,-14.3%, mean -10.4%,-13.4%, P <.001), spinal cord (max 13.3%,9.5%, P <.001) and liver (mean -29.9%,-24.3%, P <.001). No significant differences were noted for VMAT and IMRT compared with 3D-CRT for lung (V5Gy, max dose), heart (max dose) and bilateral kidneys (mean). VMAT did offer statistically significant improvement in Conformity Index, Monitor Units, lung V20Gy and mean dose as well as heart V30Gy and mean dose compared to IMRT. Conclusion: VMAT and IMRT offer excellent sparing of key organs (lung, heart) with respect to volumetric constraints. Max point doses as well as lung V5Gy, which can be an indication of low dose spread for esophageal treatment, were not conclusively different. While 3D-CRT offers acceptable treatment, VMAT should be the standard modality of radiation treatment where facilities exist.