Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, Japan.
Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, Japan.
Phys Med. 2020 Dec;80:65-74. doi: 10.1016/j.ejmp.2020.10.009. Epub 2020 Oct 26.
This study investigated the impact of lung density on the isolated lung tumor dose for volumetric modulated arc therapy (VMAT) in an inline magnetic resonance linear accelerator (MR-Linac) using the Monte Carlo (MC) simulation.
CT images of the thorax phantoms with lung tumors of 1, 2, and 3 cm diameters were converted into voxel-base phantoms with lung densities of 0.1, 0.2, and 0.3 g/cm, respectively. The dose distributions were calculated for partial-arc VMAT. The dose distributions were compared using dose differences, dose volume histograms, and dose volume indices.
In all cases, the inline magnetic field significantly enhanced the lung tumor dose compared to that at 0 T. For the 1 cm lung tumor, the inline magnetic field of 1 T increased the minimum dose of 95% of the Planning target volume (PTV D) by 14.0% in 0.1 g/cm lung density as compared to that in 0.3 g/cm at 0 T. In contrast, at 0 and 0.5 T, the PTV D in 0.3 g/cm lung density was larger than that in lung density of 0.1 g/cm. For the 2 cm lung tumor, a similar tendency to 1 cm was observed, whereas the dose impact of lung density was smaller than that for 1 cm. For the 3 cm lung tumor, the lung tumor dose was independent of lung density at 0.5 T and 1.0 T.
The inline MR-Linac with the magnetic field over 1 T can enhance the PTV D for VMAT regardless of the lung density.
本研究使用蒙特卡罗（MC）模拟，探讨在线磁共振直线加速器（MR-Linac）中肺密度对体部旋转调强放疗（VMAT）孤立肺肿瘤剂量的影响。
将直径为 1、2 和 3cm 的肺部肿瘤的胸部体模 CT 图像转换为肺密度分别为 0.1、0.2 和 0.3g/cm 的体素体模。计算部分弧 VMAT 的剂量分布。使用剂量差异、剂量体积直方图和剂量体积指数比较剂量分布。
在所有情况下，与 0T 相比，在线磁场显著提高了肺肿瘤剂量。对于 1cm 的肺肿瘤，在 0.1g/cm 的肺密度下，1T 的在线磁场使 95%计划靶区（PTV D）的最小剂量增加了 14.0%，而在 0T 下为 0.3g/cm。相比之下，在 0 和 0.5T 下，0.3g/cm 肺密度的 PTV D 大于 0.1g/cm 肺密度的 PTV D。对于 2cm 的肺肿瘤，观察到与 1cm 相似的趋势，但肺密度对剂量的影响小于 1cm。对于 3cm 的肺肿瘤，在 0.5T 和 1.0T 下，肺肿瘤剂量与肺密度无关。
磁场大于 1T 的在线 MR-Linac 可以增强 VMAT 的 PTV D，而与肺密度无关。
