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Session: Proton Therapy II [Return to Session]

Development of An Auto-Commissioning Procedure for An Electron Beam Model Applicable to Photon MLC Shaped Beams

MK Fix, D Frei, S Mueller*, G Guyer, HA Loebner, W Volken, P Manser, Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland


TU-D1030-IePD-F7-1 (Tuesday, 7/12/2022) 10:30 AM - 11:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: The commissioning of beam models for electron radiotherapy using the photon-MLC for beam shaping is currently a manual and time-consuming process. In this work an auto-commissioning procedure for a Monte Carlo (MC) beam model is developed for TrueBeam systems with electron energies from 6 to 22 MeV.

Methods: The beam model includes a main source representing the primary beam and a jaw source representing the head scatter contribution each consisting of an electron and a photon part. For the MLC MC radiation transport is performed. The auto-commissioning relies on pre-determined information from BEAMnrc simulations, in-air profile and absolute dose measurements in water for different field sizes and source to surface distances (SSDs) with in total seven measurement scans. This information is used to determine the fluence distributions, source weights, energy spectra and focal spot position and lateral intensity distribution (main source). For validation calculated and measured dose distributions in water were compared for different field sizes, SSDs and beam energies for seven TrueBeam systems. Additionally, a sternum case in an anthropomorphic phantom was considered and calculated and film measured dose distributions were compared at different SSDs.

Results: The auto-commissioning procedure was successfully applied to seven TrueBeam systems. Instead of the manual commissioning taking up to several days of calculation time and several hours of user time, the auto-commissioning is carried out in minutes. Measured and calculated dose distributions agree generally within 3% of maximum dose or 2 mm. Gamma passing rates for the sternum case using 3% (global) and 2 mm with a threshold of 10% ranged from 96% to 99%.

Conclusion: The newly developed auto-commissioning procedure allows an efficient commissioning of an MC electron beam model and eases the usage of electron radiotherapy utilizing the photon-MLC for electron beam shaping. This work was supported by Varian Medical Systems.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Varian Medical Systems.


Monte Carlo, Commissioning, Beam Shaping


TH- External Beam- Electrons: Computational dosimetry: Monte Carlo

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