Beam-quality of medical linac evaluations vary by diverse factors. Because conventional beam-quality
evaluation methods yield fragmentary results, a new beam-evaluation method is suggested, and its feasibility is evaluated. The PDDs (percentage depth doses) of 6 MV (Mega-voltage) and 10 MV photon, R (Range) of a 6 MeV (Mega Electron-voltage) and 9 MeV electron were measured and compared with the conventional evaluation methods, and the improved methods PDD¹⁰₅, PDD²⁰₁₀, PDD³⁰₂₀, PDD²⁰₅, PDD³⁰₁₀, and R⁷⁰₅₀, R⁵⁰₃₀, R⁷⁰₃₀ as the magnetic field of the bending magnet was changed to +2% to −2%, and the results were compared. The comparison showed that the improved methods exhibit a higher discrimination than the conventional methods in each energy regime. PDD¹⁰₅, PDD³⁰₂₀, PDD³⁰₁₀ and R⁷⁰₅₀, R⁵⁰₃₀ should be applied. These methods exhibit a higher discrimination in each energy regime than conventional beam-quality evaluation methods; therefore, they should be used for beam-quality evaluation according to the magnetic field variation.