The relative cellular radiosensitivity of 30 human in vitro cell lines of different histological type to high LET 62.5 MeV (p-->Be+) fast neutrons and 4 MeV photons.

It has been suggested that fast neutron therapy may have a role in the treatment of those tumours which lie within the most photon-resistant histological categories. A clinical radiobiological study by Battermann et al., however, did not support this hypothesis (Battermann, J.J. et al., Eur. J. Cancer 17: 539-548, 1981). Similarly, in a comparison of the intrinsic cellular radiosensitivity of 20 human in vitro cell lines with 4 MeV photons and 62.5 MeV (p-->Be+) neutrons, there was no correlation between RBE and photon sensitivity. However, because the range of histological cell types in this in vitro study did not include sufficient representatives of the most sensitive and resistant histological categories, it was not possible to examine the relationship between histology and the relative efficacy of fast neutrons compared with photons. The intrinsic radiosensitivity of a further 10 human in vitro cell lines has thus been measured and the results of all 30 cell lines used in a comparison of the relationship between relative neutron sensitivity and histology. These results together with those obtained by reanalysis of published data from a clinical study of the RBE of pulmonary metastases by Battermann et al. suggest that in the clinical situation, photon-resistant histology per se may not be a sufficient criterion for the choice of high LET irradiation and emphasize the need for predictive assays for individual tumours.