Efficacy of neutrons in radiotherapy

Use of neutron radiation as a potential improvement in the treatment of human cancer currently is being investigated at several radiation biology laboratories and therapy centers. Review of the relevant neutron radiobiological data for various tumors and late normal tissue effects on rodents indicates no definitive biological advantages of neutrons over conventional photon irradiation. The radiobiological data are corroborated by results from Phase I and II clinical studies at the University of Washington involving 74 neutron and 53 mixed beam (neutron/photon) treated patients with glioblastoma multiforme or advanced squamous cell carcinoma of the head and neck region. An analysis of the clinical data indicates no definitive improvement with regard to 2-yr survival rate and mean survival time for neutron-treated patients as compared to 218 photon-treated patients having similar severity of disease. Normal tissue complication rates following neutron or mixed (neutron/photon) therapy appear to be equal to or greater than those following conventional photon therapy. (author)