Evaluation of hybrid depth scanning for carbon-ion radiotherapy
Evaluation of hybrid depth scanning for carbon-ion radiotherapy
复制标题
DOI：
10.1118/1.4705357
复制
发表时间：
2012-05-01
期刊：
影响因子：
3.8
通讯作者：
Noda, Koji
中科院分区：
文献类型：
--
作者：
Inaniwa, Taku;Furukawa, Takuji;Noda, Koji
目的：在用扫描碳离子束进行放射治疗时，通过插入距离移位板或通过改变同步加速器的束提取能量，其布拉格峰沿深度方向沿着移位。在前一种技术中（距离移位器扫描：RS），距离移位器板扩大了射束尺寸，并通过核反应产生次级碎片。在后一种技术（主动能量扫描：ES）中，根据同步加速器操作周期，可能需要几秒钟才能改变光束能量，导致治疗时间较长。作者提出了一种混合深度扫描技术（混合扫描：HS），其中几个光束能量与范围移位板结合使用，以实现更精细的范围移位。在这项研究中，HS的剂量分布和治疗time.Methods的观点进行评估：假设现实的加速器和光束传输系统，作者进行了计算机模拟，使用GEANT 4蒙特卡罗代码的光束建模和治疗计划系统，以评估HS。在水模体中，在45、85和125 mm深度处生成三个具有相同尺寸60 x 60 x 60 mm（3）的靶体积，并计划对这些靶进行统一的临床剂量。比较了三种深度扫描技术的横向剂量衰减大小和峰坪比（定义为靶区平均临床剂量与入口处临床剂量的比值）以及治疗时间。SOBP中心的侧向剂量衰减大小分别为11.4、8.5和5.9 mm，RS中的侧向剂量衰减大小分别为5.7、4.8和5.9 mm，ES为4.6 mm，HS为6.6、5.7和5.0 mm。RS的峰坪比分别为1.39、1.96和2.15，ES的峰坪比分别为1.48、2.04和2.19，HS的峰坪比分别为1.47、2.03和2.18。处理时间在ES中分别为128.7、128.6和128.6 s，而在RS中分别为61.2、54.6和47.8 s，在HS中分别为43.2、44.1和44.7 s。多次散射和距离位移器引起的核反应降低了束流质量，如横向剂量衰减和峰坪比，这对于RS中的浅目标尤其明显。深度扫描时间受限于ES中的加速器周期。这增加了治疗时间的几倍。结论：这项研究表明，HS可以提供剂量分布与陡峭的横向剂量下降和更高的峰坪比相比，RS和ES。此外，与ES相比，HS的治疗时间可以大大减少。(C)2012年美国医学物理学家协会。[http：//dx.doi.org/10.1118/1.4705357]
Purpose: In radiotherapy with a scanned carbon-ion beam, its Bragg peak is shifted along the depth direction either by inserting the range shifter plates or by changing the beam-extraction energy of a synchrotron. In the former technique (range shifter scanning: RS), the range shifter plates broaden the beam size and produce secondary fragments through nuclear reactions. In the latter technique (active-energy scanning: ES), it may take several seconds to change the beam energy depending on the synchrotron operation cycle, leading to a long treatment time. The authors propose a hybrid depth scan technique (hybrid scanning: HS), where several beam energies are used in conjunction with the range shifter plates for finer range shift. In this study, HS is evaluated from the viewpoints of dose distribution and treatment time.Methods: Assuming realistic accelerator and beam-delivery systems, the authors performed computer simulations using GEANT4 Monte Carlo code for beam modeling and a treatment planning system to evaluate HS. Three target volumes with the same dimensions of 60 x 60 x 60 mm(3) were generated at depths of 45, 85, and 125 mm in water phantom, and uniform clinical dose was planned for these targets. The sizes of lateral dose falloff and the peak to plateau ratio defined as the ratio of the clinical dose averaged over the target to the clinical dose at the entrance as well as the treatment time were compared among the three depth scan techniques.Results: The sizes of lateral dose falloffs at the center of SOBP are 11.4, 8.5, and 5.9 mm for the three targets in RS, while they are 5.7, 4.8, and 4.6 mm in ES and 6.6, 5.7, and 5.0 mm in HS, respectively. The peak to plateau ratios are 1.39, 1.96, and 2.15 in RS, while they are 1.48, 2.04, and 2.19 in ES and 1.47, 2.03, and 2.18 in HS, respectively. The treatment times are 128.7, 128.6, and 128.6 s in ES, while they are 61.2, 54.6, and 47.8 s in RS and 43.2, 44.1, and 44.7 s in HS, respectively. The multiple scattering and the nuclear reaction by range shifter degraded the beam qualities such as lateral dose falloff and peak to plateau ratio, which was especially pronounced for the shallow target in RS. The depth scan timing was limited by accelerator cycle in ES. That increased the treatment time by a few times.Conclusions: This study revealed that HS can provide dose distributions with steeper lateral dose falloffs and higher peak to plateau ratio comparing to RS and comparable to ES. In addition, the treatment time can be considerably reduced in HS compared to ES. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4705357]