A heavy particle comparative study. Part II: cell survival versus depth.

Cell-survival measurements with depth of penetration were made for a series of incident doses of proton, helium, carbon, neon, argon, negative pion, neutron, and 60Co photon beams. Cultured human cells (T1) suspended in a gel-containing medium were used, and the measurements were found to be very useful in facilitating the design of ridge filters to produce iso-effects in the region of interest. Heavy charged particle beams (proton, helium, carbon, neon, and negative pion) were found to produce similar cell killing with depth of penetration. Because of saturation effects at higher LET, argon ions were less effective in killing aerated cells at depth, compared with other heavy charged-particle beams. Cell killing at depth in the region of interest, compared with that at the entrance, was not significantly different for single-field exposures when the Bragg peaks were broadened to cover a width of 10 cm. However, when two opposed fields with overlapping peaks were used, a large enhancement in killing was obtained in the peak region.