Review of the clinical results of fast neutron therapy.

The clinical results reported from the different neutron therapy centres are reviewed. Fast neutrons were shown to be useful in the treatment of locally extended inoperable salivary gland tumours (average local control rates 67% for neutrons compared to 28% for photons). For paranasal sinuses and some tumours of the head and neck area, especially extended tumours with large fixed lymph nodes, neutrons could also be of interest. By contrast, the results obtained for brain tumours were, in general, disappointing. Neutrons were shown to be beneficial in the treatment of well differentiated soft tissue sarcomas, as well as to bone- and chondrosarcomas. For locally extended prostatic adenocarcinoma, a RTOG randomized trial gave local control rates of 77% for mixed schedule compared to 31% for photons. Neutrons could be useful also for palliative treatment of melanomas. Further studies are needed in order to evaluate the benefit of fast neutrons for other localizations such as uterine cervix, bladder and rectum. It can be concluded that fast neutrons could be of interest for about 10% of the radiotherapy patients, but it is likely that the new high-energy hospital-based cyclotrons will further extend the indications of neutron therapy. However, patient selection remains one of the main problems and there is a need for development of individual predictive tests.