ABSTRACT
Kilovoltage x-rays were the first form of external beam therapy to be used. Because of their
inadequate penetrative qualities it was necessary to use multiple overlapping beams to deliver a
high dose to the tumour while keeping within tissue tolerance. At kilovoltage energies the
photoelectric effect makes a significant contribution to the absorbed dose especially in higher
atomic number materials such as bone. The soft tissue within trabecular bone receives an
enhanced dose (see Section 6.7.3), which is normally undesirable. Kilovoltage x-rays are
used mostly for superficial lesions and for palliative treatments. In modern radiotherapy
many superficial lesions could also be treated with electrons. However there are some
disadvantages in using electrons for superficial lesions. For instance, with low energy electrons
it is difficult to obtain an accurate and uniform dose for small fields or for an irregular patient
surface (see Chapter 24 and Chapter 34) and they may not be ideal for eye treatments
(see Section 21.5).
