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An Elegant Solution to Satisfy TG 142 Recommendations for Annual Electrons Output and Off-Axis Factor Constancy Versus Gantry Angle Variation

E Galhardo*, G Narayanasamy , G Deshazer , S Morrill , University of Arkansas for Medical Sciences, Little Rock, AR


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Evaluate the efficacy of a simple solution to fulfill the annual TG 142 requirements for evaluate the electron field variation for output and off-axis with the gantry rotation.

Methods: An acrylic block tray was used to create a support with fixed geometry for the Daily QA3 device (Sun Nuclear). The center of the Daily QA Device was aligned with the center of the machine reticle. The holes were drilled on the tray to match the position of the levelers, which were used to fix the QA device to the tray. An initial test was made ensuring the SSD and the center of the beam (based on the light field) did not change with the gantry in different angles. The power/data cable was connected to the device and attached to the gantry which allowed remote data collection for all the beams. Electron cone applicator was not necessary, and all the beams were tested in the service mode. The report from the daily QA device shows, beside other parameters, the output and the beam profile. It can be printed in PDF format, and used to compare with the gantry results at different angles. The system was used in two 2100EX machines, and two True Beams (Varian).

Results: All the electron energies tested passed the TG 142 criteria (±1% relative to the results for the gantry at zero degree position) for both tests: output and off-axis. The biggest relative difference was 0.7% for the profiles, and 0.5% for the output.

Conclusion: This elegant solution is an excellent alternative that provides a fast and reliable check for constancy of electron beams in various gantry angles.


Quality Assurance, Electron Therapy


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