ABSTRACT
The interest in neutron beams in radiation therapy is based solely on their radio biological
effectiveness (Raju 1980; Withers 1985; Griffin et al. 1988; see also Section 7.14). The depth-
dose characteristics of the early neutron beams were poor, resembling those of kilovoltage x-ray
and
Co g-ray beams (Fowler 1975). In Table 49.1 it can be seen that the depth-dose
characteristics of the current neutron facilities resemble those of 4-MV to 8-MV x-ray beams.
The very high density of ionisation (or high LET [linear energy transfer]) along the path of
secondary particles in neutron-irradiated media is associated with a greater response of (radio-
resistant) tumours and the reduced influence of conditions such as oxygen status, cell line,
mitotic cycle and repair phenomena (see Section 7.14).