Dosimetric Comparison between Preoperative Volumetric Modulated Arc Therapy and Fixed-field Intensity-modulated Radiotherapy for Rectal Cancer

  Objective  To compare the dosimetric characteristics of preoperative volumetric modulated arc therapy (VMAT) and fixed-field intensity-modulated radiotherapy (FF-IMRT) for rectal cancer.

  Methods  The CT images of 15 patients with rectal cancer were transferred into Eclipse planning system. FF-IMRT and VMAT plans were optimized on an Eclipse treatment planning system using beam data generated for Varian Trilogy linear accelerator. Same institutional dose-volume constraints for rectal cancer were used in both techniques. Targets and organs at risk were evaluated.

  Results  The target volume coverage could meet the requirement of described dosage in both VMAT plan group and FF-IMRT plan group. Compared with the FF-IMRT plan group, the planning target volume (PTV) 105% (PTV105%) coverage, Dmean, and Dmax significantly increased in the VMAT plan group (P=0.011, P=0.017, and P=0.006, respectively), the radiation conformity index (CI) significantly decreased(P=0.008), and the homogeneity index showed no significant difference (P=0.193). Compared with the FF-IMRT plan group, the V₅₀ of the bladder in the VMAT plan group was increased by about 15% (P=0.009), and the Dmax increased by 0.7 Gy(P=0.003); the V₃₀ of the small intestine decreased by 10%(P=0.004), and the Dmax was increased by 0.9 Gy(P=0.000); the V₁₀, V₃₀, and V₄₀ of the bone marrow reduced by 2%, 10%, and 10% (P=0.000, P=0.000, and P=0.000), and the Dmean reduced by 1.7 Gy (P=0.000); the D₅ of the left and right femoral heads reduced by 3.2 Gy and 2.4 Gy (P=0.000, P=0.000); the V₁₀, V₂₀, V₃₀, and V₄₀ of the body also significantly decreased (P=0.003, P=0.000, P=0.000, and P=0.004). The VMAT group also had significantly lower number of monitor units (MU) when compared with the FF-IMRT plan group (P=0.000).

  Conclusions  In patients with rectal cancer, preoperative VMAT can achieve equivalent or superior dose distribution compared with the FF-IMRT. In addition, VMAT can increase the number of patients treated per hour and reduce waiting time by shortening treatment time and reducing treatment MU.