NEUTRON THERAPY - THE HISTORICAL BACKGROUND

Neutron therapy was first introduced by Stone et al. in 1938, i.e. mor e than 10 years earlier than electron beam therapy and only 6 years af ter the discovery of neutrons. In spite of the impressive accomplishme nt in generating an adequate therapy beam, time was also found for car eful radiobiological studies of neutron beams. However, it was not con sidered that for a certain early reaction the late effects were much g reater with neutrons than with x-rays. The severe late sequelae in pro portion to the few good results motivated the closure of this therapy. Neutron therapy was again introduced in Hammersmith hospital at the e nd of the 1960's. The major reason seems to have been to overcome the oxygen effect. Encouraging results were reported. It was argued that t he very favourable statistics on local tumour control were obtained at the expense of more frequent and more severe complications. A clinica l trial in Edinburgh seemed to indicate this, but it was not proved in the end as the two trials differed regarding fractionation. Today abo ut 16 000 patients have been treated with neutrons. The neutron beams now used differ significantly, both regarding dose distributions and m icrodosimetrical properties, from those utilized earlier. The advantag e of neutrons is still, however, controversial. There are indications that neutron treatment may be favourable for some tumours. A careful c ost-benefit study ought to be performed before the creation of a neutr on therapy centre in Sweden as the group of patients suitable for neut rons is limited, and there may be new possibilities for improvement of photon and electron treatment with much smaller resources.