Cytological Analysis of the Response of Malignant Tumours to Irradiation as an Approach to a Biological Basis for Dosage in Radiotherapy

(1) Tumour regression as the result of irradiation is initiated by an intra-cellular response, but is carried on by an inter-cellular response which follows and plays an important part in the success of any treatment. (2) The intra-cellular reaction is directly responsible for the death of individual cells and its rate is of particular importance at the beginning of treatment. (3) The inter-cellular reaction is manifested through the repair processes, and depends on the construction of the tumour tissue as a whole. This reaction is conditioned and influenced by the intra-cellular response; in this sense it is an indirect effect of the radiation. (4) Analysis of pieces of tumour removed for biopsy before and during treatment should supply evidence as to the efficiency of the treatment given, and suggest how best to continue so as to produce complete tumour regression with the least possible irradiation. (5) With such an analysis, treatment may be adjusted so that both the intra- and the inter-cellular reactions are controlled. Satisfactory immediate tumour response has been obtained when treatment was controlled in this way with doses considerably lower than those employed by us for similar accessible tumours in the past. (6) On assumptions based on observations made on the response of accessible tumours to irradiation, a method of fractionation by increasing doses at increasing intervals has been employed for the treatment of certain deep-seated “radio-resistant” tumours as a clinical experiment. Work on similar tumours in animals has been designed to test the response to such treatment cytologically and to provide information leading to the modification of the method as applied in the treatment of human cancer.