Adjuvant vaginal cuff brachytherapy: dosimetric comparison of conventional versus 3-dimensional planning in endometrial cancer

PURPOSE: To evaluate dosimetric differences between point-based 2-dimensional (2D) vaginal brachytherapy (VBT) treatment planning technique and volume-based 3-dimensional (3D) VBT method for endometrial cancer (EC). MATERIAL AND METHODS: Ten patients with uterine-confined EC treated with VBT were included in this study. All patients received 27.5 Gy in 5 fractions. Three different treatment plans were performed for each patient: plan A for dose prescribed to the entire vaginal wall thickness delineated via computed tomography guidance, plan B for dose prescribed to the vaginal mucosa/cylinder surface, and plan C for dose prescribed to 5 mm beyond the vaginal mucosa/cylinder surface. Dose-volume histograms (DVH) of treatment volumes and organs at risk (OARs) were evaluated and compared. RESULTS: DVH analysis of target volume doses (D(100), D(95), and D(90)) showed a significant difference between plan A and plan B (p = 0.005), and plan B was found lower. D(100) for plan C was significantly higher than plan A (p = 0.009), but for D(95) and D(90), no statistically significant difference was found (p = 0.028 and p = 0.028, respectively). In terms of OARs doses, including vagina, rectum, bladder, and sigmoid, D(2cm3) doses were significantly higher in plan A than plan B (p = 0.009, p = 0.009, p = 0.005, and p = 0.005, respectively). All these doses were also significantly lower than in plan C (p = 0.005, p = 0.012, and p = 0.013, respectively), except for sigmoid (p = 0.155). CONCLUSIONS: In this dosimetric analysis, we have shown that the volume-based 3D VBT technique provides the ability to balance the target dose against the sparing of OARs. Therefore, in the new modern 3D treatment era, instead of normalization of the dose to standard reference points, customized 3D volume-based VBT planning should be recommended.