Biological effects of accelerated heavy ions. I. Single dose in normal tissue, tumors, and cells in vitro

To characterize beams of possible use in radiotherapy, the survival of jejunal crypt cells, EMT 6 tumor cells in flank tumors, and hypoxic and euoxic EMT 6 tumor cells in vitro was studied following irradiation in beams of accelerated helium, carbon, neon, or argon ions. The beams were modified with a varable-thickness absorber to give a 4-cm spread out Bragg peak (SOBP) and therefore approximated the kind of beam geometry anticipated for the clinical application of high-LET beams. The RBE was higher in cells in the EMT 6 tumor than in the gut, and higher for hypoxic cells than for euoxic cells. The RBE increased with increasing LET up to aproximately 100 keV/μm. The RBE was higher for the peak region than for the plateau region of the helium, carbon, and neon beams leading to a favorable biological depth-dose distribution measured as the peak-to-plateau RBE ratio. The argon beam had an unfavorable peak-to-plateau RBE ratio