Author: Grace Hutchinson, Daniel E. Hyer, Samuel D. Rusu, Blake R. Smith, Joel J. St-Aubin 👨🔬
Affiliation: Iowa Health Care, University of Iowa 🌍
Purpose: To assess the feasibility and consistency of the Sun Nuclear Corporation (SNC) MR conditional Quad Wedge, as an accessory to the IC Profiler-MR, and to evaluate beam output and energy in the Elekta Unity MR-Linac.
Methods: The Quad Wedge calibration was performed on the Elekta Unity MR-Linac using a 22x22 cm² field size, instead of the recommended 30x30 cm², due to field size limitations, with a 7 MV FFF beam at an SAD of 143.5 cm. The calibration required the dose at 10cm depth which was calculated using the Monaco treatment planning system. Repeatability in the energy metric (D10), flatness and symmetry, and output was evaluated by delivering 100 MU per measurement to the IC Profiler-MR with the Quad Wedge, with measurements taken over multiple days.
Results: The average central axis dose was 134.48±0.16 (1σ) cGy and coincided with dose calculated in Monaco of 133.4 cGy. Flatness and symmetry were 121.97±0.34% and 100.97±0.07% along the y-axis and 124.69±0.12% and 102.1±0.09% along the x-axis. The average D10 with the Quad Wedge across ten measurements was 71.89±0.03%. All the metrics assessed were consistent and reproducible indicating the Quad Wedge has the potential feasibility as a quality assurance tool for routine testing.
Conclusion: The data shows that the Quad Wedge can be used in conjunction with the IC Profiler-MR in a 1.5 T magnetic field safely and yields repeatable results. Thus, the Quad Wedge could be used for routine quality assurance of beam quality for the Elekta Unity MR-Linac.