Portability of IMRT QA between matched linear accelerators.

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate quality assurance (QA) is crucial for intensity-modulated radiation therapy (IMRT).
• Verifying consistency across different treatment delivery systems (TDS) is essential for reliable patient treatment.

Purpose of the Study:

• To assess if patient-specific IMRT QA measurements are interchangeable between matched TDS.
• To validate the accuracy of a common beam model for multiple TDS.

Main Methods:

• Three VMAT plans of varying complexity were delivered on three matched Varian TrueBeam TDS.
• Dose distributions were measured using a Scandidos Delta4 Phantom+ and compared to TPS calculations via gamma analysis.
• Round-robin comparisons between TDS measurements were performed using dose difference metrics.

Main Results:

• Over 95% of points passed gamma analysis (3%/3mm) when comparing measurements to calculations.
• Inter-TDS dose deviations were minimal, with median differences within 1.0% under local normalization.
• Tightest passing gamma criteria were similar across TDS, indicating high consistency.

Conclusions:

• Matched TDS deliver dose distributions meeting stringent QA tolerances.
• The common beam model accurately represents multiple TDS, enabling consistent QA.
• Small inter-TDS dose differences support the common beam model for operational improvements.