Department of Radiation Convergence Engineering, Yonsei University, Wonju, Republic of Korea.
Phys Med Biol. 2019 Dec 13;64(24):245009. doi: 10.1088/1361-6560/ab57c4.
The leaf width of a multileaf collimator (MLC) determines the dose conformity to the target volume. The objective of this study was to investigate the feasibility of a two-dimensional dynamic MLC (2DDMLC) to improve the treatment plan quality with a fixed leaf width. The treatment head of the Clinac linear accelerator with the Millennium 120 MLC was modelled with the Geant4 (for GEometry ANd Tracking) tollkit using the Monte Carlo (MC) method. The 2DDMLC produces a beam aperture by moving the MLC bank vertically to the leaf movement. Thus, the effect of the 2DDMLC motion on beam divergence and beam fluence resolution was evaluated by comparing the dose distributions between the conventional MLC motion and the 2DDMLC. Finally, the 2DDMLC was employed for dynamic conformal arc therapy for 13 brain cancer patients. The dose-volumetric parameters, including the dose delivered to 98% of the target volume (D ), percent volume given 20% of the prescribed dose (V ), and conformity index (CI) were compared with those of the conventional MLC. For the 6 MV beam of the MC model, the depth dose and lateral dose distribution differed by less than 2% between the simulation and measurement. The 2DDMLC did not significantly influence beam divergence and sharpened the beam. In clinical use, the dose delivered to the target was almost identical between the 2DDMLC and conventional MLC (D = 29.74 Gy versus 29.71 Gy, p = 0.18). The CI was improved with the use of the 2DDMLC (CI = 1.49 versus 1.47, p = 0.14). Moreover, irradiation of normal tissue was reduced with the 2DDMLC compared with conventional MLC (V = 17.22% versus 17.45%, p < 0.001). The 2DDMLC improved the dose conformity to the target volume and reduced the irradiation of the normal tissue compared with the conventional MLC.
多叶准直器（MLC）的叶片宽度决定了靶区剂量的适形度。本研究旨在探讨二维动态多叶准直器（2DDMLC）在使用固定叶片宽度的情况下改善治疗计划质量的可行性。采用蒙特卡罗（MC）方法，使用 Geant4（用于几何和追踪）工具包对 Clinac 直线加速器的治疗头和 Millennium 120 MLC 进行建模。2DDMLC 通过垂直于叶片运动移动叶片来产生射束孔径。因此，通过比较常规 MLC 运动和 2DDMLC 之间的剂量分布，评估了 2DDMLC 运动对射束发散和射束通量分辨率的影响。最后，为 13 名脑癌患者实施了 2DDMLC 动态适形弧形治疗。比较了剂量-体积参数，包括 98%靶区体积接受的剂量（D）、20%处方剂量的体积（V）和适形指数（CI），与常规 MLC 的参数进行比较。对于 MC 模型的 6 MV 射线，模拟和测量之间的深度剂量和侧向剂量分布差异小于 2%。2DDMLC 对射束发散没有显著影响，并使射束变锐。在临床应用中，2DDMLC 和常规 MLC 对靶区的剂量输送几乎相同（D=29.74 Gy 对 29.71 Gy，p=0.18）。使用 2DDMLC 可提高 CI（CI=1.49 对 1.47，p=0.14）。此外，与常规 MLC 相比，2DDMLC 减少了对正常组织的照射（V=17.22% 对 17.45%，p<0.001）。与常规 MLC 相比，2DDMLC 改善了靶区剂量适形度，减少了对正常组织的照射。
