Survival of Clonogenic Murine Epithelioma Cells Exposed to 52 MeV Proton Beam Produced from the Cyclotron at INS

Abstract

Squamous carcinoma in WHT/Ht mice were exposed to 52 MeV proton beam produced from FM cyclotron at INS, University of Tokyo. The biological effects of the proton beam were compared to those of 250 kVp X-rays. The survivng fraction of epithelioma cells irradiated in vivo was studied using TD 50 assay. RBE values for protons were calculated from the ratio of the X-ray and proton D₀ values and were 1.0±0.2 for aerobic cells and 1.0±0.1 for hypoxic cells. OER value of protons was the same as that of 250 kVp X-rays. The repair of potentially lethal damage of cells exposed to peak protons was smaller compared to X-rays; namely repair ratios were 4.0 for 800 rad proton dose and 9.8 for 1, 000 rad X-ray dose.