All depends. IIRC: X-ray for the first half-inch or less, then Iridium gamma-ray for the next inch or so, then Cobalt gamma-ray up to about 4-inches, then Linear Accelerator to get up to a foot or thicker. {left out cyclotron for 2-inches or so].
X-ray it possible to take to the field, but very difficult. Cyclotron and Linear Accelerator are essentially impossible to use outside of a lab.