ABSTRACT
Megavoltage* photon beams are the most widely used radiation in radiotherapy because
of their greater penetration compared to kilovoltage beams. Early megavoltage radiotherapy
was carried out with cobalt-60 teletherapy units, and these are still the most suitable where the
technical infrastructure is not adequate for the support of linear accelerators (IAEA 1998)
Linear accelerators have the advantage of more penetrating beams, the versatility of the choice
of beam energy, a smaller penumbra at the edge of the beam, and they deliver a higher dose rate.
They also have the advantage that the source does not need to be replaced and the old source
disposed of. A major advantage of megavoltage beams is the effect of skin sparing brought
about by dose build-up (see Section 22.3.1). This effect is greater the higher the energy.
