Gamma contamination of neutron beams

The recent publication of the proceedings of the International Meeting on High LET Radiations in Clinical Radiotherapy highlights the diversity of ways in which neutron dose is quoted (Barendsen et al., 1979). Radiobiologists and radiotherapists in different centres quoted: (a) Neutron dose alone, DN; (b) total (neutron + contaminating γ) dose, DN+γ or (c) an effective neutron dose, obtained by assuming that the RBE of neutrons is three and therefore adding one third of the γ dose to the pure neutron dose, Deft = DN +Dγ/3.