Systematic evaluation of four-dimensional hybrid depth scanning for carbon-ion lung therapy
Systematic evaluation of four-dimensional hybrid depth scanning for carbon-ion lung therapy
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DOI：
10.1118/1.4792295
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发表时间：
2013-03-01
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：
Mori, Shinichiro;Furukawa, Takuji;Noda, Koji
目的：用扫描束照射移动靶需要全面了解器官运动以及稳健的剂量误差缓解技术。作者研究了分次呼吸运动对碳离子笔形束相位控制再扫描肺肿瘤剂量分布的影响。为了解决密度的变化，他们使用4DCT datas.Methods：剂量分布的各种重新扫描方法，如简单的层重新扫描（LR），体积重新扫描，和相位控制重新扫描（PCR），计算肺体模和肺部患者的研究。为了确保真实性，他们将扫描参数（如扫描速度和能量变化时间）设置为与我们机构使用的参数相似。根据临床相关性确定评价指标，包括（i）相位控制重新扫描、（ii）扫描方向、（iii）靶运动（方向和幅度）、（iv）呼吸周期和（v）处方剂量。通过使用射束场特异性靶体积计算斑点权重图，该靶体积考虑了各个呼吸相位的范围变化。为了强调分次内运动对剂量分布的影响，未使用呼吸门控。累积剂量计算通过应用B样条为基础的变形图像配准，和相位控制分层重扫描（PCRL）和相位控制体积重扫描（PCRV）的结果进行了比较。结果：对于体模研究，简单的LR是无法提高剂量分布的数量增加的重扫描。相位控制技术。没有重新扫描（1 x PCRL和1 x PCRV），由于扫描速度降低，剂量一致性显著降低。相比之下，4 x PCRL或更高剂量显著且一致地改善了剂量分布。PCRV显示干扰效应，但一般而言，重新扫描次数越多，剂量均匀性越好。扫描方向垂直于运动方向的单个PCRL/PCRV的剂量分布显示出较大的热点/冷点;然而，对于两种方法，随着重新扫描次数的增加，这种效应消失。对于其他剂量指标，如靶运动（SI/AP）、振幅（6-22 mm峰-峰）和呼吸周期（3.0-5.0 s），获得了类似的观察结果。对于四次或更多次重新扫描，两种方法均显示出显著更好的结果，尽管体积PCR更受干扰效应的影响，这导致一些剂量分布的严重退化。临床实例显示出与体模研究相同的趋势。剂量评估指标（D95，Dmax/Dmin，均匀性指数）的PCRL/PCRV的数量增加，但与PCRL是更robust.Conclusions：PCRL需要一个更长的治疗时间比PCRV的高数量的重新扫描在近红外光谱扫描系统，但更强大。尽管四次或四次以上的再扫描提供了良好的剂量均匀性和一致性，但作者更倾向于对临床病例使用更多的再扫描，以进一步最大限度地减少器官运动引起的剂量降低效应。(C)2013年美国医学物理学家协会。[http：//dx.doi.org/10.1118/1.4792295]
Purpose: Irradiation of a moving target with a scanning beam requires a comprehensive understanding of organ motion as well as a robust dose error mitigation technique. The authors studied the effects of intrafractional respiratory motion for carbon-ion pencil beam scanning with phase-controlled rescanning on dose distributions for lung tumors. To address density variations, they used 4DCT data.Methods: Dose distributions for various rescanning methods, such as simple layer rescanning (LR), volumetric rescanning, and phase-controlled rescanning (PCR), were calculated for a lung phantom and a lung patient studies. To ensure realism, they set the scanning parameters such as scanning velocity and energy variation time to be similar to those used at our institution. Evaluation metrics were determined with regard to clinical relevance, and consisted of (i) phase-controlled rescanning, (ii) sweep direction, (iii) target motion (direction and amplitude), (iv) respiratory cycle, and (v) prescribed dose. Spot weight maps were calculated by using a beam field-specific target volume, which takes account of range variations for respective respiratory phases. To emphasize the impact of intrafractional motion on the dose distribution, respiratory gating was not used. The accumulated dose was calculated by applying a B-spline-based deformable image registration, and the results for phase-controlled layered rescanning (PCRL) and phase-controlled volumetric rescanning (PCRV) were compared.Results: For the phantom study, simple LR was unable to improve the dose distributions for an increased number of rescannings. The phase-controlled technique. without rescanning (1 x PCRL and 1 x PCRV) degraded dose conformity significantly due to a reduced scan velocity. In contrast, 4 x PCRL or more significantly and consistently improved dose distribution. PCRV showed interference effects, but in general also improved dose homogeneity with higher numbers of rescannings. Dose distributions with single PCRL/PCRV with a sweep direction perpendicular to motion direction showed large hot/cold spots; however, this effect vanished with higher numbers of rescannings for both methods Similar observations were obtained for the other dose metrics, such as target motion (SI/AP), amplitude (6-22 mm peak-to-peak) and respiratory period (3.0-5.0 s). For four or more rescannings, both methods showed significantly better results, albeit that volumetric PCR was more affected by interference effects, which lead to severe degradation of a few dose distributions. The clinical example showed the same tendencies as the phantom study. Dose assessment metrics (D95, Dmax/Dmin, homogeneity index) were improved with an increasing number of PCRL/PCRV, but with PCRL being more robust.Conclusions: PCRL requires a longer treatment time than PCRV for high numbers of rescannings in the NIRS scanning system but is more robust. Although four or more rescans provided good dose homogeneity and conformity, the authors prefer to use more rescannings for clinical cases to further minimize dose degradation effects due to organ motion. (C) 2013 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4792295]