Commissioning a secondary dose calculation software for a 0.35 T MR‐linac

Abstract

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.

Magnetic field induced dose effects in radiation therapy using MR‐linacs

“…45,47,49 The 0.35 T MRIdian beam also characterized an asymmetry crossline profile. 61 A Monte Carlo simulation showed that the negative side…”

“…Lower magnetic field strength is expected to have reduced dose effects 45,47,49 . The 0.35 T MRIdian beam also characterized an asymmetry crossline profile 61 . A Monte Carlo simulation showed that the negative side of the crossline penumbra in the lung slab region was 3 mm larger than the inline penumbra 45 …”

An integrated and fast imaging quality assurance phantom for a 0.35 T magnetic resonance imaging linear accelerator

“…Since the 0.35 T ViewRay MRIdian MRL was first introduced in 2017, numerous papers have been published regarding MRL acceptance testing/commissioning and quality assurance (QA) [8] , [9] , [10] , [11] , [12] , [13] . Due to the presence of magnetic fields, the imaging QA of these MRL systems became critical to the accuracy of treatment delivery, such as MRI localization, voxel sizing, and distortion correction [14] , [15] .…”

ART2Dose: A comprehensive dose verification platform for online adaptive radiotherapy

“…Price et al first commissioned commercial software RadCalc (LifeLine Software,Austin,TX,USA) to MRIdian system and investigated point dose analysis (with and without magnetic field) on the adaptive plans. 7 Wang et al developed an in-house Monte Carlo system built upon graphics processing unit (GPU)-accelerated dose planning method (gDPM) on the MRIdian system to validate adaptive plans with consideration of magnetic fields and achieved within 2.3 min on average for implementation in ART. 8 For the Unity, several studies explored the utility and performance of existing commercial software, such as with RadCalc 9 and MU2Net (DOSIsoft, France), 10 and the hybrid of in-house developed GPU-accelerated Monte Carlo-based dose verification module into a commercial software ArcherQA.…”

“…Price et al. first commissioned commercial software RadCalc (LifeLine Software, Austin, TX, USA) to MRIdian system and investigated point dose analysis (with and without magnetic field) on the adaptive plans 7 . Wang et al.…”