Author: Andrew Clarke Grice, Evan A. Silverstein 👨🔬
Affiliation: Sutter Medical Foundation, Sutter Health 🌍
Purpose: To implement an efficient and effective process for Electron beam matching between 5 Varian True Beams (TB).
Methods: We adapted the Varian installation/acceptance process for TBs, whereby R50 is the electron beam energy specifier and measured with an IC Profiler/QuadWedge combination. R50 is modified to within 0.07 cm of an expected value through changes of the Bending Magnet Current. The expected R50 values from commissioning are based on PDDs with a 15x15 cone.
15x15 PDDs were then measured on 1 machine with Bending Magnet Current modifications to achieve the expected R50 value. Calibration files with an in-house IC Profiler/QuadWedge were created and used on 4 other True Beams to match R50. 15x15 PDDs were performed during annual measurements for additional verification of R50.
Results: R50 indicated by the IC Profiler could be achieved within 0.03cm of the expected value. PDD measurements after modifications show excellent agreement of R50, R80, and R90 with values < 0.1cm between each machine. A rough estimate of the required Bending Magnet Current change could be determined as a 0.1A change typically resulted in ~0.01cm change in R50.
Conclusion: Once calibration files are created, the IC Profiler/QuadWedge combination allows for a quick and accurate modification of R50 for each electron energy. Quantification of R50, R80, and R90 with PDDs after modifications, verified that R50 was a useful beam energy specifier.