Neutron therapy--the historical background

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