RBE of π - Beams in the Bragg Peak Region Determined with Polyploidy Induction in Mammalian Cells Irradiated in Vivo

Abstract

The Relative Biological Effective -ness (RBE) of components of a [pi]-meson beam, contaminated with electrons and [pi] decay products, was determined for polyploidy induction in a mammalian cell system in vivo. The RBE in the plateau region of this beam was 1 relative to cobalt-60 gamma rays, whereas in the Bragg peak region it was 2.15. For pion effects only in the peak region, RBE was 2.37; for "star" effects only, it was 0.64. On the basis of theory and preliminary observation, it is believed that RBE values for cell killing exceed the values found for polyploidy induction. The diminished oxygen effect and low ratio of surface dose to depth dose displayed by [pi] beams having a Bragg peak region, coupled with the Bragg peak region''s relatively high RBE, indicate that [pi] beams may be useful in tumor radiotherapy.