Author: Matthew Stephen Andriotty, Taoran Cui, Josh Kilian-Meneghin, Ke Nie, Xiao Wang, Zhenyu Xiong, Ning J. Yue, Yin Zhang 👨🔬
Affiliation: Rutgers Cancer Institute of New Jersey, RWJBarnabas Health 🌍
Purpose: To investigate the potential impact of the Elekta Unity’s 1.5T magnetic field upon the performance of a conventional linac installed in an adjacent vault.
Methods: The linac vaults for this facility are oriented in a line with parallel linac orientation, and isocenters separated by approximately 13 meters. Measurements were taken pre and post magnet ramp-up to assess the changes in magnetic field strength permeating the vault and any changes in conventional linac performance. Measurements of the magnetic field in multiple locations were acquired with a gauss meter. The mechanical vs MV imaging performance was evaluated with a SNC Multi-Met Winston Lutz (MMWL) test phantom with 6x. The phantom was not removed from the treatment table between these tests. Finally, the flatness, symmetry, and output vs gantry angle for all energies was tested utilizing a gantry mounted SNC IC Profiler.
Results: Peak gauss meter at the wall located closest to the Elekta Unity isocenter increased from the background value to 0.1mT post magnet ramp-up. At the conventional linac isocenter the reading never increased above background. An analysis of other points surrounding the Elekta Unity vault confirms that the magnetic field strength reaches a maximum along the Elekta Unity axis (bore direction). A peak value of 0.3mT was acquired in the service room directly behind the Elekta Unity isocenter with a distance of approximately 3.9 meters. All tested field-target coincidence differences for the MMWL phantom were within 1mm pre and post magnet ramp-up. Flatness, symmetry, and output vs gantry measurements were all within TG142 1% tolerance, as well as within 1% raw measurement comparison pre and post magnet ramp-up.
Conclusion: With an isocenter separation of approximately 13 meters and a parallel linac orientation, there are no discernable impacts upon conventional linac performance caused by the adjacent Elekta Unity.