Commissioning of the Varian TrueBeam linear accelerator: a multi-institutional study

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Latest generation linear accelerators (linacs), including TrueBeam and TrueBeam STx, feature advanced capabilities like high-dose-rate flattening-filter-free (FFF) photon modes and novel control systems.
• These advanced features necessitate thorough evaluation and commissioning to ensure safe and effective clinical implementation.

Purpose of the Study:

• To evaluate the commissioning experience of five TrueBeam linacs at three different institutions.
• To compare dosimetric and mechanical parameters across multiple TrueBeam machines.

Main Methods:

• Analysis of acceptance and commissioning data from five TrueBeam linacs with 120-leaf MLCs.
• Comparison of photon beam profiles, PDD curves, output factors, electron cone factors, isocenter accuracy, MLC transmission, and dosimetric leaf gap (DLG).
• Inclusion of end-to-end testing and IMRT commissioning procedures.

Main Results:

• Excellent agreement in gantry/collimator isocentricity (0.27-0.28 mm) and overall mechanical accuracy (0.46-0.68 mm) across institutions.
• Consistent dosimetric data, with minimal variation in MLC DLG, transmission, photon beam quality (%dd(10)x), and output factors.
• Minor variations observed in output factors for small field sizes and electron cone factors for small cone sizes.

Conclusions:

• Multi-institutional TrueBeam commissioning data demonstrated excellent agreement, validating machine performance.
• This comprehensive dataset serves as a crucial reference for future TrueBeam commissioning, enhancing safety and quality in radiation therapy.