Embodiments of the invention provide systems and methods for achromatically bending beam of charged particles by about 90° during radiation treatment. A system may include first, second, third, and fourth bending magnets serially arranged along the particle beam path. The first and fourth bending magnets are configured to generate a positive field gradient that defocuses the particle beam in the bend plane. The second and third bending magnets are configured to generate a negative field gradient that focuses the particle beam in the bend plane. The first, second, third, and fourth bending magnets collectively bend the particle beam by about 90°, e.g., by about 22.5° each.