ABSTRACT
Purpose: To compare the dosimetric performance of vaginal intensity-modulated brachytherapy (IM-BRT) applicator and single- (SC-BRT) and multi-channel brachytherapy (MC-BRT) applicators for vaginal cuff brachytherapy (VC-BRT). Material and methods: Fifteen patients with uterine-confined endometrium cancer who received adjuvant VC-BRT were included in this study. IM-BRT, SC-BRT, and MC-BRT treatment plans were created for two different clinical target volume (CTV) definitions: 1. Standard CTV, called CTVs; and 2. Virtually defined CTV, called CTVv, with asymmetrical tumor extension > 5 mm in thickness. Plan comparison was performed using dose-volume histogram (DVH) and treatment planning parameters. Results: According to DVH analysis, D98 for CTVv and D2 for both CTVs and CTVv showed statistically significant differences between IM-BRT and SC-BRT plans, but there was no significant difference between IM-BRT and MC-BRT plans in terms of D98 and D2 for both CTVs and CTVv. Additionally, for CTVv plans, IM-BRT was found to be significantly superior to SC-BRT for the rectum (D2cc, V5Gy, and V7Gy), bladder (D2cc and V7Gy), and small bowel (D2cc, V5Gy, and V7Gy). On the other hand, DVH parameters of the sigmoid showed large difference between IM-BRT and SC-BRT plans, but it was not statistically significant. Similarly, the use of IM-BRT applicator demonstrated a noticeable dose reduction in all defined OARs when compared with MC-BRT applicator, but statistically significant for the rectum V7Gy (p = 0.03) only. Conclusions: While the IM-BRT applicator is still in pre-clinical phase, our investigation demonstrated the proof-of-concept in real patient treatment plans with promising dosimetric results compared with SC-BRT and MC-BRT plans in selected patient group.
ABSTRACT
PURPOSE: To design a novel high-dose-rate intracavitary applicator which may lead to enhanced dose modulation in the brachytherapy of gynecological cancers. MATERIAL AND METHODS: A novel brachytherapy applicator, auxiliary equipment and quality control phantom were modeled in SketchUp Pro 2017 modeling software and printed out from a MakerBot Replicator Z18 three-dimensional printer. As a printing material polylactic acid (PLA) filament was used and compensator materials including aluminum, stainless-steel and Cerrobend alloy were selected according to their radiation attenuation properties. To evaluate the feasibility of the novel applicator, two sets of measurements were performed in a Varian GammaMed iX Plus high-dose rate iridium-192 (192Ir) brachytherapy unit and all of the treatment plans were calculated in Varian BrachyVision treatment planning system v.8.9 with TG43-based formalism. In the first step, catheter and source-dwell positioning accuracy, reproducibility of catheter and source positions, linearity of relative dose with changing dwell times and compensator materials were tested to evaluate the mechanical stability of the designed applicator. In the second step, to validate the dosimetric accuracy of the novel applicator measured point dose and two-dimensional dose distributions in homogeneous medium were compared with calculated data in the treatment planning system using PTW VeriSoft v.5.1 software. RESULTS: In mechanical quality control tests source-dwell positioning accuracy and linearity of the designed applicator were measured as ≤ 0.5 mm and ≤ 1.5%, respectively. Reproducibility of the treatment planning was ≥ 97.7% for gamma evaluation criteria of 1 mm distance to agreement and 1% dose difference of local dose. In dosimetric quality control tests, maximum difference between measured and calculated point dose was found as 3.8% in homogeneous medium. In two-dimensional analysis, the number of passing points was greater than 90% for all measurements using gamma evaluation criteria of 3 mm distance to agreement and 3% dose difference of local dose. CONCLUSIONS: The novel brachytherapy applicator met the necessary requirements in quality control tests.
