目的:MR-Linac集成了MRI扫描仪和线性加速器,以提供自适应放射治疗。优越的组织对比度和实时成像可以使临床医生有信心减少计划目标体积(PTV)的裕度。这项研究的目的是验证MR-Linac系统在治疗运动目标时的剂量学准确性,并使用不同的运动模式和适应方法评估误差。
方法:我们使用4D动态胸腔幻影(CIRSMRgRT008Z)对ElektaUnity(Elekta)进行了端到端测试,比较测量剂量和计划剂量。移动的体模在肿瘤中有四个测量位置,肝脏,肾,和具有PTW30013离子室的脊髓区域。对于七个不同的运动模式,我们首先使用慢速扫描协议获取模拟CT,在此基础上,我们生成了参考计划。治疗技术是标准调强放射治疗(IMRT)。我们测试了两个适应工作流程:适应位置(ATP)和适应形状(ATS)。使用二极管阵列体模(SunNuclearInc.)测量三维(3D)分布,以检查作为常规QA过程的一部分的剂量分布精度。我们还在传统直线加速器上进行了端到端测试。最后,我们使用SPSS统计22.0(Inc.,芝加哥,IL,美国)进行数据分析。
结果:所有预处理参考计划和交付计划均具有出色的QA结果,相对伽马分析的通过率优于95%(2%/2mm标准)。MR-Linac的自适应规划产生了质量计划。目标中测量的剂量与计算的剂量一致。
结论:所研究的MR-Linac系统的适应性治疗符合肿瘤运动的预期表现。目标的轮廓可以在3DMR上可视化并精确地轮廓化,以进行在线计划。在不同的运动模式下,测量剂量和计算剂量之间的差异在临床上是可接受的.
OBJECTIVE: MR-Linac integrates an MRI scanner and a linear accelerator to provide adaptive radiation treatment. Superior tissue contrast and real-time imaging can give the clinicians confidence to reduce the margins of the planning target volume (PTV). The purpose of this study was to verify the dosimetric accuracy of an MR-Linac system in treating a moving target and assess the error with different motion patterns and adaptation methods.
METHODS: We performed an end-to-end test for Elekta Unity (Elekta) using the 4D Dynamic Thorax Phantom (CIRS MRgRT 008Z), comparing the measured and planned dose. The moving phantom had four measurement locations in the tumor, liver, kidney, and spinal cord regions with a PTW30013 ion chamber. For seven different motion patterns, we first acquired simulation CT using a slow-scanning protocol, based on which we generated reference plans. The treatment technique was the standard intensity-modulated radiation therapy (IMRT). We tested both adaptation workflows: the Adapt-to-Position (ATP) and the Adapt-to-Shape (ATS). The three-dimensional (3D) distribution was measured using a diode array phantom (Sun Nuclear Inc.) to check the dose distribution accuracy as part of the routine QA process. We also performed end-to-end tests on a conventional Linac. Finally, we used SPSS Statistics 22.0 (Inc., Chicago, IL, USA) for data analysis.
RESULTS: All pretreatment reference plans and delivered plans had excellent QA results with a better than 95% passing rate of relative gamma analysis (2%/2 mm criteria). The adaptive planning for MR-Linac produced quality plans. The measured dose in the target agreed with the calculated dose.
CONCLUSIONS: The adaptive treatment on the MR-Linac system investigated met the expected performance with tumor motions. The outline of the target could be visualized and accurately contoured on the 3D MR for online planning. Under different motion patterns, the difference between the measured and calculated dose was acceptable clinically.