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

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.