Survival of Oxygenated and Hypoxic Tumor Cells in the Extended-Peak Regions of Heavy Charged-Particle Beams

Abstract

The survival of oxygenated and hypoxic cells of the R-1 rat rhabdomyosarcoma tumor line in suspension culture has been measured at several positions in the plateau and the extended peak regions of carbon-, neon-, and argon-ion beams. Both the carbon and neon beams had 14- and 23-cm ranges in water; the argon beam has a 13-cm range. Peak regions extended to both 4 and 10 cm were studied for each ion species. In the 10-cm extended peak, OER values were close to 2.0 for the carbon-ion beam, 1.9-1.5 for the neon beam, and 1.4-1.2 for neutrons, while the argon OER in the extended peak is lower than that for neutrons. The RBE values increased through the carbon peak region, were large and relatively constant through the neon peak region, and decreased through the argon peak region, thus reflecting the changing effective LET that results from the changing energies and the different charges of the particles. An analysis of the effectiveness of the different ion beams for killing hypoxic cells in the peak relative to killing oxygenated cells in the plateau implies that, for single-port irradiations, carbon ions may be the most advantageous charged-particle species for the treatment of deep-seated hypoxicmore » tumors. However, for tumors at shallow depths, the present results indicate that carbon and neon ions are similar in their effectiveness. Argon ions may be superior for the treatment of poorly oxygenated tumors close to the body surface.« less