Osaka Heavy-Ion Therapy Center, Osaka, Japan.
Department of Carbon Ion Radiotherapy, Osaka University Graduate School of Medicine, Osaka, Japan.
Med Phys. 2022 Feb;49(2):801-812. doi: 10.1002/mp.15403. Epub 2021 Dec 28.
Herein, we report the methods and results of the Hitachi carbon-ion therapy facility commissioning to determine the optimum values of the magnitude of movement and repaint number in respiratory-gated irradiation.
A virtual-cylinder target was created using the treatment-planning system (VQA Plan), and measurements were performed to study the effects of respiratory movements using a two-dimensional ionization-chamber array detector and a phantom with movable wedge and stage. For simulations, we selected a 10 × 10 × 10 cm cubic irradiation pattern with a uniform physical dose and two actual cases of liver-cancer treatments, whose prescribed doses were 60 Gy(RBE)/4 fraction (Case 1) and 60 Gy(RBE)/12 fraction (Case 2). We employed two types of repainting methods, one produced by the algorithm of VQA Plan (VQA algorithm) and the other by ideal repainting. The latter completely repeats all spots with set number of repaintings. We performed flatness calculations and gamma analysis to evaluate the effects of each condition.
From the measurements, the gamma passing rates for which the criteria were 3%/3 mm exceeded 95% for displacements in the head-to-tail direction if the repaint number was greater than 3 and the magnitude of the residual motions was less than 5.0 mm. In simulations with the cubic irradiation pattern, the gamma passing rates (with criteria of 2%/2 mm) exceeded 95% when the magnitude of the residual motions was 3.0 mm and the repaint number was greater than 3. When the repaint number was set to 4 in the VQA with the actual liver cases, the flatness results for Case 2 was minimal. For ideal repainting, the flatness results for all ports fell within ∼3.0% even when the magnitude of the residual motions was 5.0 mm if the repaint number was 6. However, the flatness was less than 3.0% for almost all ports if the magnitude of the residual motions was less than 3.0 mm with a repaint number of 4 in case of both types of repaint methods.
At our facility, carbon-ion radiotherapy can be provided safely to a moving target with residual motions of 3.0 mm magnitude and with a repaint number of 4.
在此，我们报告日立碳离子治疗设备调试的方法和结果，以确定呼吸门控照射中运动幅度和重绘次数的最佳值。
使用治疗计划系统（VQA Plan）创建虚拟圆柱靶，使用二维电离室阵列探测器和带有可移动楔形和台的体模进行测量，以研究呼吸运动的影响。对于模拟，我们选择了一个 10×10×10cm 的立方照射模式，具有均匀的物理剂量和两个肝癌治疗的实际病例，其规定剂量分别为 60Gy（RBE）/4 分次（病例 1）和 60Gy（RBE）/12 分次（病例 2）。我们采用了两种重绘方法，一种是由 VQA Plan 算法产生的（VQA 算法），另一种是理想重绘的。后者完全重复所有设定重绘次数的点。我们进行了平坦度计算和伽马分析，以评估每种情况的效果。
从测量结果来看，如果重绘次数大于 3 且残余运动幅度小于 5.0mm，则头对头方向的位移伽马通过率标准为 3%/3mm 时超过 95%。在立方照射模式的模拟中，如果残余运动幅度为 3.0mm 且重绘次数大于 3，则伽马通过率（标准为 2%/2mm）超过 95%。当实际肝脏病例的 VQA 中的重绘数设置为 4 时，病例 2 的平坦度结果最小。对于理想重绘，如果重绘次数为 6，则即使残余运动幅度为 5.0mm，所有端口的平坦度结果都在约 3.0%以内。然而，如果残余运动幅度小于 3.0mm 且重绘次数为 4，则两种重绘方法的几乎所有端口的平坦度都小于 3.0%。
在我们的设备中，对于残余运动幅度为 3.0mm 且重绘次数为 4 的移动目标，可以安全地提供碳离子放射治疗。
