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. Megavoltage beams are not only more penetrating, but they have the major benefit that the maximum dose is delivered below the skin surface (see Section 22.3.1). In addition, because the principal interaction with tissue is through the Compton effect, the locally absorbed dose is not dependent on the atomic number of the tissue, and the dose to bone is not enhanced.