Oolbekkink Stijn, Borman Pim T S, Wolthaus Jochem W H, van Asselen Bram, van Lier Astrid L H M W, Dunn Stephanie, Koenig Grant R, Hartman Nick, Kheirkhah Niusha, Raaymakers Bas W, Fast Martin F
Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
IBA QUASAR, Modus Medical Devices Inc., London, Ontario, Canada.
Med Phys. 2025 May;52(5):3391-3397. doi: 10.1002/mp.17632. Epub 2025 Jan 31.
Novel motion-compensated treatment techniques on the MR-linac can address adverse intra-fraction motion effects. These techniques involve beam gating or intra-fraction adaptations of the treatment plan based on real-time magnetic resonance imaging (MRI) performed during treatment. For quality assurance (QA) of these workflows, a multi-purpose motion platform is desirable. This platform should accommodate various phantoms, enabling multiple QA workflows.
This study aims to evaluate the new IBA QUASAR Motion MR Platform for use in the 1.5 T MR-linac.
The motion platform was assessed for several magnetic resonance (MR) characteristics, including spurious noise generation and B0&B1 homogeneity. In addition, the motion platform's motion accuracy and beam attenuation were assessed. An application was shown with a ScandiDos Delta4 Phantom+ MR demonstrating patient-specific plan QA of gated treatments using time-resolved dosimetry that includes motion based on a patient's respiratory motion trace.
All MR characterization measurements were within the set tolerances for MRI QA. The motion platform motion accuracy showed excellent agreement with the reference, with a standard deviation of the amplitude of 0.01 mm (20 kg load) for the motor's self-estimated positions and 0.22 mm (no load) for the images acquired with the electronic portal imager. Beam attenuation was found to be 11.8%. The combination of the motion platform and Delta4 demonstrated motion-included dosimetry at high temporal and spatial resolutions. Motion influenced the measured dose in non-gated treatments by up to -20.1%, while gated deliveries showed differences of up to -1.7% for selected diodes.
The motion platform was found to be usable in a 1.5 T magnetic field, and for all MR characterization experiments, no influence from the motion platform was observed. This motion platform enables to perform motion-included QA, with a measurement device of choice.
磁共振直线加速器（MR-linac）上的新型运动补偿治疗技术可解决分次内运动的不良影响。这些技术包括束流门控或基于治疗期间进行的实时磁共振成像（MRI）对治疗计划进行分次内调整。对于这些工作流程的质量保证（QA），需要一个多功能运动平台。该平台应能容纳各种体模，实现多种QA工作流程。
本研究旨在评估用于1.5T MR-linac的新型IBA QUASAR Motion MR平台。
对运动平台的几个磁共振（MR）特性进行了评估，包括杂散噪声产生和B0&B1均匀性。此外，还评估了运动平台的运动精度和束流衰减。展示了一个使用ScandiDos Delta4 Phantom+ MR的应用，通过时间分辨剂量测定法对门控治疗进行患者特异性计划QA，该方法包括基于患者呼吸运动轨迹的运动。
所有MR特性测量结果均在MRI QA的设定公差范围内。运动平台的运动精度与参考值显示出极佳的一致性，电机自估计位置的振幅标准偏差为0.01毫米（20千克负载），电子门静脉成像仪采集图像的标准偏差为0.22毫米（无负载）。发现束流衰减为11.8%。运动平台和Delta4的组合在高时间和空间分辨率下展示了包含运动的剂量测定。在非门控治疗中，运动对测量剂量的影响高达-20.1%，而门控输送时，选定二极管的差异高达-1.7%。
发现该运动平台可在1.5T磁场中使用，并且在所有MR特性实验中，未观察到运动平台的影响。该运动平台能够使用选定的测量设备进行包含运动的QA。
