A methology is proposed for extracting and analyzing specific fast neutron effects on radiotherapy. This should be applied to the 1,500 patients treated at NIRS, Chiba in the past ten years. As the patients have been treated with different modalities based on generally combined radiation or neutron boost techniques at first the biologically equivalent doses per fraction for the photon and neutron component according to the Ellis concept were derived. In a second step treatment parameters, as the dose components and total dose as well as diagnostic parameters (tumor typing, grading and staging) will be related to the clinical outcome (survival, local control etc.). This may be done by multivariate discriminant or survival analysis.