The role of fast neutrons in radiooncology--a critical appraisal.

The contribution of fast neutrons to local tumour control has been investigated worldwide since the mid-60's in more than 20 institutions. The high expectations anticipated from the promising results of experimental studies could not be adequately realized in the clinic. The late normal tissue damage was unacceptable due to poor depth dose characteristics and further technical limitations of the first generation low-energy machines. Even with sophisticated therapy planning systems and high-energy cyclotrons as well as comparable late normal tissue damage as witnessed after photons, only a few tumour entities have responded superiorly to fast neutrons. These particularly include macroscopic tumours of the salivary glands, prostate and, potentially, soft and osseous tissues. The role of fast neutrons for head and neck cancer has not yet been definitely proved. For bladder-, cervical- and rectal carcinomas, non-small cell lung-, pancreatic- and breast cancers as well as malignant gliomas, no therapeutic benefit as compared with photons was observed in the case of macroscopic residual or inoperable recurrent tumours.