Radiosensitivity and Biological Properties of Two Tumour-types Indigenous to the Same Host

Summary

A study was undertaken to provide information regarding the comparative effects of single and divided x-ray doses on the regression of experimental tumours. This is a first report. Two types of mammary tumours, a slower-growing, epithelial-cell type designated DBAH, and a faster-growing, spindle-cell type designated DBAG, both indigenous to the inbred DBA/212 strain of mice and propagated in parent hosts, were x-irradiated in vivo. A total dose of 10 000 r was employed in one exposure and in 2, 4 and 8 equal fractions delivered at 24-hour intervals to tumours ranging in size from 12–15 mm in diameter. The greatest effect on both types of tumours was obtained when 10 000 r was employed in two equal doses and the least effect when the dose was divided into eight equal fractions. Instances of local recurrences and distant metastases were more frequent in mice with the DBAG tumour treated with fractionated doses than in mice with the DBAH tumour. Quantitative data are recorded in tables 1 and 2. A contrasting pattern of cellular response to x-irradiation of these two types of tumour is demonstrated in the microphotographs.