FAST-NEUTRON THERAPY - THE UK EXPERIENCE

Following conflicting results from Hammersmith and Edinburgh, the 62.5 MeV (p --> Be+) Douglas cyclotron was installed at Clatterbridge in o rder to carry out further studies with fast neutrons. Several features were incorporated into the study design to achieve as unbiased as pos sible a comparison between 62.5 MeV neutrons and conventional 8 MV x-r ay therapy. Interim analysis of 151 patients in the pelvic study in th e autumn of 1989 revealed a trend towards a worse survival in the neut ron therapy group which soon became significant, leading to study term ination in February 1990. The reasons for this diminished survival wer e unclear; with no significant difference in morbidity. Although the i ncidence of metastases was initially higher in the neutron patients th an the photon patients this difference was not sufficient to explain t he survival difference. Considerable morbidity would be expected from photon therapy using the same fractionation as was used in the neutron arm of the trial. If further neutron therapy at this energy is planne d consideration should be given to the use of smaller fractions.