SU‐FF‐T‐102: Clinical Beam Tuning of Low‐Energy Electron Beams: Matching Varian and Siemens Linear Accelerators

Purpose: Tuning nominal energies on linear accelerators is useful for matching machines of different vendors and for altering energies to match clinical needs. In this study we investigated matching a Varian 2100EX 4MeV electron beam to a Siemens Primus 5MeV electron beam. Method and Materials: The 4MeV beam of a Varian 2100EX linear accelerator was tuned via a significant shunt‐voltage adjustment to match the 5MeV beam of a Siemens Primus linear accelerator. The percent depth‐depth dose (PDD) curves and off‐axis profiles for multiple field sizes were compared to validate the beam matching. Data was collected with a CC04 cylindrical chamber in water and with a parallel‐plate ion chamber in plastic water® (Computer Imaging Reference Systems, Inc., Norfolk, VA). Results: The PDD from the parallel‐plate and cylindrical ion chambers agreed within 1.1% and 2.5% for the 3×3cm² and 10×10cm² fields respectively. There was also good agreement in the PDD of the tuned 4MeV (referred to as 4MeV* post‐tuning) and 5MeV beams. The depth of Dmax was identical. Differences in the practical range were only 1mm. The PDD had the best agreement for the 3×3cm² field (⩽1.5% to depth of D90), followed by the 10×10cm² field (⩽2.0% to depth of D90) and the 25×25cm² field (⩽2.5% to depth of D90). Larger disagreements occurred in the dose falloff region beyond D90, typically 2–7%. The off‐axis profiles for the 4MeV* and 5MeV beams showed good agreement for the 10×10cm² field (⩽2%). However, there was a substantial loss in flatness for the 25×25cm² field (5.5% for 4MeV*, 2.4% for 5MeV). We believe these differences are caused by the original 4MeV Varian scattering foil, which was not changed to reflect the greater energy of the 4MeV* beam. Conclusion: The Varian 4MeV and Siemens 5MeV beams were successfully matched, allowing oncologists to utilize these machines interchangeably. © 2007, American Association of Physicists in Medicine. All rights reserved.

Duke Scholars

Author Jennifer Colleen O'Daniel Radiation Oncology