Enhancing patient-specific quality assurance in MR-guided radiation therapy: A fluence-based method using log files

Abstract

Background: Patient-specific quality assurance (PSQA) is crucial in radiation therapy to ensure accurate and safe dose delivery. The Elekta Unity MR-Linac system, which combines MRI with a linear accelerator, presents unique challenges for conventional PSQA methods due to its adaptive capabilities and the presence of a magnetic field. Purpose: This study introduced a novel PSQA method for the Elekta Unity MR-Linac system, utilizing treatment log files and fluence map verification to provide a more efficient alternative to traditional measurement-based techniques. Methods: The proposed method analyzed log file data, including monitor units (MU), multi-leaf collimator (MLC) positions, and jaw positions, comparing them with treatment planning system (TPS) values. Fluence maps were generated for each gantry angle and evaluated using gamma analysis. A user-friendly interface was developed to streamline the process. Results: The method was tested on nine stereotactic body radiation therapy (SBRT) cases, showing strong concordance between planned and delivered parameters. MU deviations were within 0.5 MU, X-jaw and MLC leaf position deviations were under 1 mm, and gamma analysis of fluence maps achieved passing rates above 98% for all gantry angles. Conclusion: This log file-based PSQA method offered distinct advantages over traditional measurement-based approaches, including reduced QA time, direct assessment of the delivered plan, and comprehensive evaluation of treatment parameters. This method provided an efficient and accurate alternative PSQA solution for MR-guided adaptive radiotherapy.