Comparison between protracted and conventional dose rates of irradiation on the growth of the Bp8 mouse ascites sarcoma.
Four days after inoculation, in vivo growing Bp8 mouse ascites sarcoma was irradiated with 1.75, 2.5 and 5 Gy at a dose rate of 0.0185 Gy/min. The results were compared with those obtained previously at a dose rate of 1.33 Gy/min. Using flow-cytometry and the mitotic index, the total number of tumour cells and the proportion of cells in the various parts of the cell cycle were determined up to 10 days after irradiation. In addition, from sequential analyses of the total number of cells in the various compartments of the cell cycle, the flow of cells through cell cycle was calculated. The total number of tumour cells at the plateau phase of growth, the mitotic index and flow calculations indicated that protracted irradiation was more effective than short-time irradiation following 2.5 Gy; no differences were found following 1.75 Gy, and a lesser effect following 5 Gy. While the cells during protracted irradiation were effectively blocked in G2 and in split-dose experiments a good repair capacity has been demonstrated, redistribution of cells in the cell cycle can apparently not explain the results. Induction of repair, dependent both on dose rate and on total dose, may explain the higher efficiency of protracted irradiation.
D000818:Animals; D002455:Cell Division / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D051379:Mice; D008940:Mitotic Index; D011879:Radiotherapy Dosage; D012513:Sarcoma, Experimental / Q000473:pathology / Q000532:radiotherapy*