Abstract
Cell survival was measured for rat rhabdomyosarcoma R1 tumors irradiated in the distal 4-cm peak region of 400 MeV/u carbon- and neon-ion beams. An in vitro assay for clonogenic capacity was used to determine the surviing fraction of cells following in vivo tumor irradiation. Based on the response to 225-kV x rays under air-breathing and hypoxic conditions, it was estimated that the chronically hypoxic fraction of cells is 35%. From survival curves for tumors irradiated in air-breathing rats, RBE/sub 0/ /sub 1/ values determined at the 10% survival level were 2.0 and 3.1 for the peak carbon- and neon-ion radiation, respectively. Under hypoxic conditions, RBE/sub 0/ /sub 1/ values for peak carbon and neon ions were, respectively, 2.0 and 3.3 A diminshed oxygen effect was observed for the neon-ion relative to the carbon-ion radiation. Values of RBE for the two heavy charged-particle beams were also determined from measurements of tumor regression and regrowth following irradiation. Based on the ratio of x-ray to charged-particle doses required to produe a growth delay of 50 days, RBE/sub 50/ values for peak carbon and neon ions were 2.3 and 2.9, respectively. These RBE values are similar to those obtained in the cell survival studiesmore » and, to the extent that they reflect a large population of hypoxic cells, indicate that peak neon ions have a greater therapeutic potential than peak carbon ions for the treatment of radioresistant hypoxic tumors.« less
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call