Dynamic Modulated Brachytherapy for Cervical Cancer
D Han*, M Webster, D Scanderbeg, C Yashar, W Song, UCSD Medical Center, La Jolla, CAWE-A-108-6 Wednesday 8:00AM - 9:55AM Room: 108
Purpose: We propose two new intra-uterine tandem designs that are capable of creating non-isotropic 192-Ir dose distributions and give unprecedented dose conformality for treatment of cervical cancer.
Methods: The first tandem design, MC6, has 6 peripheral holes of 1-mm diameter, and the in-between-space filled with tungsten (18.0 g/cc), wrapped in delrin (1.41 g/cc). The second design, DMBT, has 19 holes of 1-mm diameter, each occupied by gold wires (19.3 g/cc) that can slide in and out (with motors), and the in-between-space filled with silicon (1.14 g/cc). MCNPX Monte Carlo was used to simulate the resulting non-isotropic dose distributions. An in-house developed HDR brachytherapy planning platform, with intensity modulated planning capability using Simulated Annealing and Constrained-Gradient Optimization algorithms, was used to plan 36 patient cases and compare with the clinically treated, conventional T&O applicator-based plans. For the proposed tandem designs, the plans were optimized with the same ovoids in place, as the conventional T&O plans.
Results: All 36 plans were prescribed 6Gy and normalized to D90=6Gy and V100=95%. Generally, the plan qualities were markedly better using MC6 and DMBT, with DMBT usually performing the best overall. Mean 2cc/0.1cc doses to the bladder were 9.14+-0.78/9.32+-0.80Gy, 6.87+-0.57/7.05+-0.59Gy, and 6.61+-0.51/6.74+-0.52Gy, for T&O, MC6, and DMBT, respectively. For the rectum, they were 5.78+-0.69/5.92+-0.70Gy, 5.17+-0.52/5.30+-0.52Gy, and 4.92+-0.50/5.04+-0.50Gy. For the sigmoid, they were 5.23+-0.58/5.34+-0.59Gy, 5.04+-0.56/5.21+-0.57Gy, and 4.86+-0.51/5.03+-0.52Gy. The most improvement was in the bladder dose and this was due to the horseshoe-like wrapping of the bladder around the CTV, thus benefitting the most with the dose conformation enhancements achieved by the proposed designs. The CTV dose heterogeneity index (DHI) was 2.43+-0.01, 2.30+-0.01, and 2.26+-0.01, respectively.
Conclusions: We have shown two tandem designs that advance the conformality of image-guided cervix HDR, in congruence with the current trend of 3D image based planning to maximize the therapeutic ratio.