Direction Modulated Brachytherapy (DMBT) for Cervical Cancer

Purpose/Objective(s): A new intra-uterine tandem design is proposed for creating non-isotropic 192-Ir dose distribution and give unprecedented dose conformality for treatment of cervical cancer. Materials/Methods: A DMBT design was made of non-magnetic high density tungsten alloy (18.0g/cc) cylinder with 6 peripheral grooves running along the length for an 192-Ir HDR afterloader source to travel along. The groove has 1.3mm in diameter and evenly distributed on the tungsten alloy, which has a diameter of 5.4mm. The tungsten alloy is enclosed in a total diameter of 6.4mm polyoxymethylene tube (1.41 g/ cc). For calculating dose distribution, 51 million decay events are simulated on Monte Carlo simulation and resulting non-isotropic dose distributions. 75 plans (5 fraction [fx] of 15 patient cases), clinically treated with conventional tandem & ovoids (T&O) applicator, were replanned on an in-house development HDR brachytherapy planning platform, which is intensity modulated planning capability using Simulated Annealing and Constrained-Gradient Optimization algorithms. All DMBT plan results were compared against the T&O clinically treated plans, which were normalized to match the HRCTV V100 coverage. Also all the plans were optimized with the same ovoids in place as the conventional T&O plans. Results: Generally, the plan qualities were markedly better using DMBT. Among the 75 plans, an average bladder, rectum, and sigmoid dose (D2cc) reduction were 0.59 0.87 Gy (8.5 28.7%), 0.48 0.55 Gy (21.1 27.2%), 0.10 0.38 Gy (40.6 214.9%) among the 75 plans, respectively. The bladder dose, 3.20Gy (40.8%), was the best single plan reduction, due to the horseshoe-like bladder around the CTV. The best sigmoid dose reduction was 1.26Gy (27.5%) for endophytic growth type cervical cancer. Overall, the most dose reduction was caused by the dose flexibility of DMBT. The HRCTV D90 was similar with 6.55 0.96 Gy for T&O and 6.59 1.06 for DMBT. Conclusions: The new tandem designs that advance the conformality of image-guided cervix HDR were created in congruence with the current trend of 3D image based planning to maximize the therapeutic ratio. Author Disclosure: D. Han: None. M.J. Webster: None. D.J. Scanderbeg: None. C. Yashar: None. D. Choi: None. B. Song: None. S. Devic: None. A. Ravi: None. W.Y. Song: None.