Sohn James J, Polizzi Mitchell, Kang Sang-Won, Ko Woo-Hyeong, Cho Yong-Hyun, Eom Keun-Yong, Chung Jin-Beom
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, United States.
Department of Radiation Oncology, Seoul National University Bundang Hospital, Seongnam, South Korea.
Front Oncol. 2022 Feb 10;12:829529. doi: 10.3389/fonc.2022.829529. eCollection 2022.
In high-dose-rate (HDR) brachytherapy, an anisotropic dose distribution may be desirable for achieving a higher therapeutic index, particularly when the anatomy imposes challenges. Several methods to deliver intensity-modulated brachytherapy (IMBT) have been proposed in the literature, however practical implementation is lacking due to issues of increased delivery times and complicated delivery mechanisms. This study presents the novel approach of designing a patient-specific inner shape of an applicator with 3D metal printing for IMBT using an inverse plan optimization model.
The 3D printed patient-specific HDR applicator has an external shape that resembles the conventional brachytherapy applicator. However, at each dwell position of the HDR source, the shielding walls in the interior are divided into six equiangular sections with varying thicknesses. We developed a mathematical model to simultaneously optimize the shielding thicknesses and dwell times according to the patient's anatomical information to achieve the best possible target coverage. The model, which is a bi-convex optimization problem, is solved using alternating minimization. Finally, the applicator design parameters were input into 3D modeling software and saved in a 3D printable file. The applicator has been tested with both a digital phantom and a simulated clinical cervical cancer patient.
The proposed approach showed substantial improvements in the target coverage over the conventional method. For the phantom case, 99.18% of the target was covered by the prescribed dose using the proposed method, compared to only 58.32% coverage achieved by the conventional method. For the clinical case, the proposed method increased the coverage of the target from 56.21% to 99.92%. In each case, both methods satisfied the treatment constraints for neighboring OARs.
The study simulates the concept of the IMBT with inverse planning using the 3D printed applicator design. The non-isotropic dose map can be produced with optimized shielding patterns and tailored to individual patient's anatomy, to plan a more conformal plan.
在高剂量率近距离放射治疗中，为了获得更高的治疗指数，尤其是在解剖结构带来挑战时，各向异性剂量分布可能是理想的。文献中已提出几种实施调强近距离放射治疗（IMBT）的方法，但由于治疗时间增加和输送机制复杂等问题，实际应用仍有所欠缺。本研究提出了一种新颖的方法，即使用逆向计划优化模型，通过3D金属打印设计用于IMBT的患者特异性施源器内部形状。
3D打印的患者特异性高剂量率施源器的外形类似于传统近距离放射治疗施源器。然而，在高剂量率源的每个驻留位置，内部的屏蔽壁被分成六个等角的部分，厚度各不相同。我们开发了一个数学模型，根据患者的解剖信息同时优化屏蔽厚度和驻留时间，以实现最佳的靶区覆盖。该模型是一个双凸优化问题，使用交替最小化求解。最后，将施源器设计参数输入到3D建模软件中，并保存为3D可打印文件。该施源器已在数字体模和模拟临床宫颈癌患者上进行了测试。
与传统方法相比，所提出的方法在靶区覆盖方面有显著改善。对于体模情况，使用所提出的方法，99.18%的靶区被规定剂量覆盖，而传统方法仅达到58.32%的覆盖。对于临床病例，所提出的方法将靶区覆盖从56.21%提高到99.92%。在每种情况下，两种方法均满足相邻危及器官的治疗约束。
本研究使用3D打印施源器设计通过逆向计划模拟了IMBT的概念。可以通过优化屏蔽模式生成非各向同性剂量分布图，并根据个体患者的解剖结构进行定制，以制定更适形的计划。
