ABSTRACT
Kilovoltage x-ray beams are useful for the treatment of skin lesions and shallow tumours, but
for deep-seated tumours, the dose that can be delivered is limited by the high skin dose. Mega-
voltage beams are not only more penetrating, but they have themajor benefit that themaximum
dose is delivered below the skin surface (see Section 22.3.1). In addition, because the principal
interactionwith tissue is through theCompton effect, the locally absorbed dose is not dependent
on the atomic number of the tissue, and the dose to bone is not enhanced.
