Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri, USA.
J Appl Clin Med Phys. 2022 Mar;23(3):e13452. doi: 10.1002/acm2.13452. Epub 2022 Feb 15.
Secondary external dose calculations for a 0.35 T magnetic resonance image-guided radiation therapy (MRgRT) are needed within the radiation oncology community to follow safety standards set forth within the field. We evaluate the commercially available software, RadCalc, in its ability to accurately perform monitor unit dose calculations within a magnetic field. We also evaluate the potential effects of a 0.35 T magnetic field upon point dose calculations. Monitor unit calculations were evaluated with (wMag) and without (noMag) a magnetic field considerations in RadCalc for the ViewRay MRIdian. The magnetic field is indirectly accounted for by using asymmetric profiles for calculation. The introduction of double-stacked multi-leaf collimator leaves was also included in the monitor unit calculations and a single transmission value was determined. A suite of simple and complex geometries with a variety field arrangements were calculated for each method to demonstrate the effect of the 0.35 T magnetic field on monitor unit calculations. Finally, 25 patient-specific treatment plans were calculated using each method for comparison. All simple geometries calculated in RadCalc were within 2% of treatment planning system (TPS) values for both methods, except for a single noMag off-axis comparison. All complex muilt-leaf collimator (MLC) pattern calculations were within 5%. All complex phantom geometry calculations were within 5% except for a single field within a lung phantom at a distal point. For the patient calculations, the noMag method average percentage difference was 0.09 ± 2.5% and the wMag average percentage difference was 0.08 ± 2.5%. All results were within 5% for the wMag method. We performed monitor unit calculations for a 0.35 T MRgRT system using a commercially available secondary monitor unit dose calculation software and demonstrated minimal impact of the 0.35 T magnetic field on monitor unit dose calculations. This is the first investigation demonstrating successful calculations of dose using RadCalc in the low-field 0.35 T ViewRay MRIdian system.
对于磁共振图像引导放射治疗（MRgRT）0.35T 系统，放射肿瘤学界需要进行二次外照射剂量计算，以遵循该领域规定的安全标准。我们评估了市售软件 RadCalc 在磁场中准确进行监测单位剂量计算的能力。我们还评估了 0.35T 磁场对点剂量计算的潜在影响。在 RadCalc 中，我们分别在考虑（wMag）和不考虑（noMag）磁场的情况下对 ViewRay MRIdian 进行了监测单位计算。通过使用不对称轮廓进行计算，间接考虑了磁场。还在监测单位计算中引入了双层多叶准直器叶片，并确定了单个透射值。对于每种方法，我们计算了一系列具有各种场排列的简单和复杂几何图形，以演示 0.35T 磁场对监测单位计算的影响。最后，我们使用每种方法计算了 25 个患者特定的治疗计划进行比较。RadCalc 中计算的所有简单几何图形的结果均在两种方法的治疗计划系统（TPS）值的 2%以内，除了单个 noMag 轴外比较外。所有复杂多叶准直器（MLC）模式计算均在 5%以内。除了单个肺部体模中的远场点外，所有复杂的体模几何图形计算均在 5%以内。对于患者计算，noMag 方法的平均百分比差异为 0.09±2.5%，wMag 方法的平均百分比差异为 0.08±2.5%。所有结果在 wMag 方法中均在 5%以内。我们使用市售的二次监测单位剂量计算软件对 0.35T MRgRT 系统进行了监测单位计算，并证明了 0.35T 磁场对监测单位剂量计算的影响很小。这是首次证明在低场 0.35T ViewRay MRIdian 系统中成功使用 RadCalc 进行剂量计算的研究。
