The comparative survival of clonogenic cells of a murine epithelioma irradiated in vivo with 250 kVp X rays, 60Co gamma rays, or negative pions produced by the cyclotron at TRIUMF.

Squamous carcinomas in WHT/Ht mice were exposed to the biomedical pion beam at TRIUMF. The biological effects of the pion beam were compared to those of 250 kVp x rays. The dose rates were 2-3 rad/min. (.02-.03 Gy/min.) for pions and 56 rad/min. (.56 Gy) for x rays. The surviving fraction of epithelioma cells irradiated in vivo was studied using the TD50 assay. RBE values for pions were calculated from the ratio of the x-ray and pion D0 values and were found to be 1.6 +/- 0.3 for oxic cells and 2.1 +/- 0.4 for hypoxic cells. OER values were 1.8 +/- 0.5 for pions and 2.4 +/- 0.4 for 250 kVp x rays.