With proton therapy, the risk of damage to healthy tissues and potential side effects is reduced because the beam is designed to stop and deposit dose
within the tumor site rather than passing all the way through the patient.
Compared to step-and-shoot techniques that deliver multiple overlapping segments to modulate beam intensity at a limited number of angle positions, tomotherapy provides more degrees of freedom to deposit dose
to the target while avoiding critical structures.
Whereas X-rays deposit dose
all along their path and continue to deposit dose
beyond the depth of the tumor, PBRT deposits most of its dose at a specific depth, determined by the initial energy of the beam, and then stops entirely.