An evaluation of the results of neutron therapy trials.

Twenty-five randomised clinical trials have been completed which have investigated the value of fast neutron therapy. The results of these trials are reviewed in terms of the reported rates of local tumour control and late morbidity. The trials have included patients with cancers of the head and neck region, brain, lung, pancreas, cervix, bladder and rectum. None has demonstrated neutrons to be advantageous compared with photons. Two trials of locally advanced prostate cancer have given conflicting results. A trial of mixed schedule therapy has demonstrated improved local tumour control and survival. A trial of neutrons alone for similar stage disease has not shown any therapeutic advantages. It is still claimed that salivary gland tumours may be more effectively treated by neutrons but the clinical trial results are not definitive. Late morbidity after neutron therapy is a persistent cause for concern and often has been unacceptably high. There is no convincing evidence that fast neutrons are either as safe or as effective in cancer control as photon therapy.