Already answered but I wanted to put it in layman’s terms in case anybody was wondering. When they do even and ‘old school’ x-ray rad treatment the beam is rotated around multiple axis centred on the treatment location. The tech line up your markings to put the treatment location at the correct spot the.n the machine rotates With another rotating head on it as well so the beam path hits different tissue during the treatment except at the treatment location. Surrounding tissue gets a significantly lower dose than the target location.

I did 25 rounds in 2021, it’s crazy how sophisticated even the outdated treatment methods are.