Comparing log file to measurement-based patient-specific quality assurance

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Technological advancements enable patient-specific quality assurance (QA) without time-consuming measurements.
• Log file-based QA systems offer a potential alternative to traditional measurement-based methods.

Purpose of the Study:

• To compare the agreement of the log file-based Mobius QA system with measurement-based QA methods (ArcCHECK and portal dosimetry).
• To evaluate the error detection sensitivity of the Mobius QA system compared to measurement-based methods.
• To assess the clinical significance of detected errors.

Main Methods:

• 100 patient plans and 10 phantom plans were analyzed using Mobius, ArcCHECK, and portal dosimetry on a VitalBeam machine.
• Gamma evaluation (3%/2 mm) was performed according to TG218 recommendations.
• Receiver operating characteristic curves were used to compare error sensitivities, with clinical significance assessed by dose recalculation.

Main Results:

• Mobius demonstrated non-inferiority to ArcCHECK and portal dosimetry in passing plans at the TG218 action limit.
• Mobius showed good sensitivity to collimator and gantry errors but not MLC bank shifts.
• Systematic errors were clinically significant only at large magnitudes and were flagged by QA checks.

Conclusions:

• The Mobius QA system is a viable alternative and supplement to existing measurement-based QA methods.
• Mobius can identify real-time treatment delivery discrepancies, enhancing QA practices.
• Maintaining routine machine QA is essential for the reliability of log file data used in QA.