An investigation of using log-file analysis for automated patient-specific quality assurance in MRgRT.

Objective: Adaptive radiation therapy (ART) is an integral part of MR-guided RT (MRgRT), requiring a new RT plan for each treatment fraction and resulting in a significant increase in patient-specific quality assurance (PSQA). This study investigates the possibility of using treatment log-file for automated PSQA.

Method: All treatment plans were delivered in 1.5T Unity MR-Linac (Elekta). A Unity compatible version of LinacView (Standard Imaging) was commissioned to automatically monitor and analyze the log-files. A total of 220 fields were delivered and measured by ArcCheck -MR (Sun Nuclear) and LinacView. Thirty incorrectly matched fields were also delivered to check for error detection sensitivity. The gamma analysis, γ, with 3%, 3 mm criteria was used in both ArcCheck -MR and LinacView. Additionally, the gantry angle, jaws, and multileaf collimators (MLC) positions reported in the log-file were compared with plan positions using TG-142 criteria.

Result: The γ (3%, 3 mm) for the 190 plans were found to be between the range of 72.5%-100.0% and 95.4%-100.0% for ArcCheck -MR and LinacVeiw, respectively. All the delivered gantry angle and jaws were found to be within 0.2° and 2 mm. MLCs that were outside the guard leaves or under the diaphragms were found to have more than 1.0 mm discrepancy. This was attributed to the linac internal override for these MLCs and had no dosimetric impact. Excluding these discrepancies, all MLC positions were found to be within 1.0 mm. The γ (3%, 3 mm) for the 30 incorrectly matched fields were found to be 3.9%-84.8% and 0.1%-64.4% for ArcCheck -MR and LinacVeiw, respectively.

Conclusion: Significant ranked correlation demonstrates the automated log-file analysis can be used for PSQA and expedite the ART workflow. Ongoing PSQA will be compared with log-file analysis to investigate the longer term reproducibility and correlation.