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Session: Therapy: Electron Treatment [Return to Session]

Customize Electron Energy Beams On TrueBeam Linear Accelerators

S Gao*, M Muruganandham, W Du, J Ohrt, R Kudchadker, P Balter, UT MD Anderson Cancer Center, Houston, TX


SU-IePD-TRACK 6-4 (Sunday, 7/25/2021) 3:00 PM - 3:30 PM [Eastern Time (GMT-4)]

Purpose: To facilitate optimal planning, we implemented two new electron energy beams (7- and 11-MeV) on two Varian TrueBeam linacs.

Methods: To better meet clinical needs we worked with the vendor to create two additional customized electron energies without hardware modifications. For each of these beams we set the bending magnet current and then optimized other beam specific parameters to achieve depths of 50% ionization (I50) of 2.9-cm for 7-MeV and 4.2-cm for the 11-MeV beams with the 15×15cm^2 cone. This was done using an Ionization Chamber Profiler (ICP, Sun Nuclear) with double-wedge-phantom (DW). Beams were steered and balanced to optimize symmetry using the ICP. After all parameters were set with the vendor, a full commissioning was done including measuring beam profiles, PDDs, output factors (OF) at standard and extended SSDs. The measured data was compared between two linacs and also against the calculated values from our TPS model (RayStation) following MPPG 5.a.

Results: The values of I50 initially determined with ICP/DW agree to those from PDD scanned in-water phantom within 0.2-mm for 7- and 11-MeV on both linacs. Comparison of the beam characteristics from two linacs indicated that, flatness and symmetry were in agreement within 0.4%, point-by-point differences of PDD are within 0.01±0.3% for 7- and 0.01±0.3% for 11-MeV beams. The OF ratios between the two linacs were 1.000±0.007 for 7- and 1.004±0.007 for 11-MeV beams. The TPS calculations and measurements indicated that the point-to-point ratios (low-gradient regions) were 0.2±0.8% and Distance-To-Agreements (high-gradient regions) were 0.8±0.6mm, all meet the MPPG5.a criteria.

Conclusion: We were able to add in two new beam energies with no hardware modifications. The tuning of the new beams was facilitated by the ICP/DW system allowing us to have the procedures done in a few hours and achieve highly consistent results across two linacs.



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