title: Response of fibrosarcoma cell subpopulations to small doses of radiation delivered in situ.
abstract: The survival of cells from 2 tumor subpopulations after gamma-ray doses ranging from 1 to 19 Gy was determined using a lung colony assay. Methylcholanthrene-induced fibrosarcomas grown in the hind legs of C3H/Kam pathogen-free mice were irradiated in situ when the tumors were 8-10 mm in diameter. Single cell suspensions prepared from excised tumors were separated on a linear density gradient, and the clonogenicity of predominantly oxic Band 2 (density 1.08 g/cm3) and predominantly hypoxic Band 4 (density 1.14 gm/cm3) cells was measured. The surviving fraction of cells after doses of 1, 2, and 3 Gy was estimated from that measured after total doses of 5 Gy = 5 X 1 Gy, 10 Gy = 5 X 2 Gy, and 15 Gy = 5 X 3 Gy, under the assumption of equal effect per fraction (checked by estimating survival at 3 Gy after different numbers of fractions). Very little curvature was evident in the survival curves of Band 2 and Band 4 cells (beta/alpha = .013-.034 Gy-1). The initial segment of the survival curve of the predominantly oxic Band 2 cells was steeper (1Do = 3.6 Gy) than that of the predominantly hypoxic Band 4 cells (1Do = 5.2 Gy); both remained linear over a large range, to doses in excess of 3 Gy. These results imply that these tumor subpopulations will be insensitive, in their response to multifractionated regimens, to changes in size of dose per fraction in the range 0 to 3 Gy, a trait shared by two acutely responding normal tissues (murine testis and jejunum).
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000528:radiation effects*; D002999:Clone Cells / Q000528:radiation effects; D003114:Colony-Forming Units Assay; D004307:Dose-Response Relationship, Radiation; D005354:Fibrosarcoma / Q000139:chemically induced / Q000473:pathology / Q000532:radiotherapy*; D008748:Methylcholanthrene; D051379:Mice; D008809:Mice, Inbred C3H; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000139:chemically induced / Q000473:pathology / Q000532:radiotherapy; D011879:Radiotherapy Dosage
chemical_list: D008748:Methylcholanthrene