网格大小对前列腺癌螺旋断层放疗的影响。

The Impact of the Grid Size on TomoTherapy for Prostate Cancer.

作者信息

Kawashima Motohiro, Kawamura Hidemasa, Onishi Masahiro, Takakusagi Yosuke, Okonogi Noriyuki, Okazaki Atsushi, Sekihara Tetsuo, Ando Yoshitaka, Nakano Takashi

机构信息

Gunma University Heavy Ion Medical Center, Maebashi, Japan.

Department of Radiation Oncology, Gunma University Graduate School of Medicine, Maebashi, Japan.

出版信息

J Med Phys. 2017 Jul-Sep;42(3):144-150. doi: 10.4103/jmp.JMP_123_16.

DOI:10.4103/jmp.JMP_123_16

PMID:28974860

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC5618461/

Abstract

Discretization errors due to the digitization of computed tomography images and the calculation grid are a significant issue in radiation therapy. Such errors have been quantitatively reported for a fixed multifield intensity-modulated radiation therapy using traditional linear accelerators. The aim of this study is to quantify the influence of the calculation grid size on the dose distribution in TomoTherapy. This study used ten treatment plans for prostate cancer. The final dose calculation was performed with "fine" (2.73 mm) and "normal" (5.46 mm) grid sizes. The dose distributions were compared from different points of view: the dose-volume histogram (DVH) parameters for planning target volume (PTV) and organ at risk (OAR), the various indices, and dose differences. The DVH parameters were used Dmax, D2%, D2cc, Dmean, D95%, D98%, and Dmin for PTV and Dmax, D2%, and D2cc for OARs. The various indices used were homogeneity index and equivalent uniform dose for plan evaluation. Almost all of DVH parameters for the "fine" calculations tended to be higher than those for the "normal" calculations. The largest difference of DVH parameters for PTV was Dmax and that for OARs was rectal D2cc. The mean difference of Dmax was 3.5%, and the rectal D2cc was increased up to 6% at the maximum and 2.9% on average. The mean difference of D95% for PTV was the smallest among the differences of the other DVH parameters. For each index, whether there was a significant difference between the two grid sizes was determined through a paired -test. There were significant differences for most of the indices. The dose difference between the "fine" and "normal" calculations was evaluated. Some points around high-dose regions had differences exceeding 5% of the prescription dose. The influence of the calculation grid size in TomoTherapy is smaller than traditional linear accelerators. However, there was a significant difference. We recommend calculating the final dose using the "fine" grid size.

摘要

由于计算机断层扫描图像的数字化和计算网格导致的离散化误差是放射治疗中的一个重要问题。对于使用传统直线加速器的固定多野调强放射治疗，此类误差已被定量报道。本研究的目的是量化计算网格大小对断层治疗中剂量分布的影响。本研究使用了十个前列腺癌治疗计划。最终剂量计算分别采用了“精细”（2.73毫米）和“常规”（5.46毫米）两种网格大小。从不同角度比较了剂量分布：计划靶区（PTV）和危及器官（OAR）的剂量体积直方图（DVH）参数、各种指数以及剂量差异。PTV的DVH参数采用Dmax、D2%、D2cc、Dmean、D95%、D98%和Dmin，OAR的DVH参数采用Dmax、D2%和D2cc。用于计划评估的各种指数为均匀性指数和等效均匀剂量。几乎所有“精细”计算的DVH参数都倾向于高于“常规”计算的参数。PTV的DVH参数中最大差异是Dmax，OAR的最大差异是直肠D2cc。Dmax的平均差异为3.5%，直肠D2cc最大增加到6%，平均增加2.9%。PTV的D95%平均差异在其他DVH参数差异中最小。对于每个指数，通过配对检验确定两种网格大小之间是否存在显著差异。大多数指数存在显著差异。评估了“精细”和“常规”计算之间的剂量差异。高剂量区域周围的一些点差异超过处方剂量的5%。断层治疗中计算网格大小的影响小于传统直线加速器。然而，仍存在显著差异。我们建议使用“精细”网格大小计算最终剂量。