Response of multicellular tumor spheroids to multiple fractions of negative PI-mesons and X-rays

Abstract Two cell lines in the form of multicellular tumor spheroids (MTS) were used as test systems to compare fractionated negative pi meson (pion) radio-therapy (10 daily fractions in 11 to 14 days) with single-fraction pions, as well as single and 10-fraction doses of X rays. The pion irradiations were carried out in the proximal and distal regions of a modulated 8 cm pion peak. The results showed: (1) The relative biological effectiveness (RBE) for pion increased significantly with fractionation, and this increase in RBE with fractionation was greater in the cell line with the smaller D q in single cell systems. (2) The RBE was the same in the proximal and distal portions of the pion peak. (3) The amount of reduction in the threshold region with 10 fractions of pions was less than a simple multiple of the amount of reduction of the threshold region with a single fraction of pions.