RBE values of high-energy electron beams at various depths in cultured mammalian cells.

Mouse leukemic cells (L5178Y) were used to determine the RBE values of high energy electron beams at various depth doses in a water phantom at 37°C. The RBE values of 10, 20 and 30 MeV electrons relative to 180 kV X-rays were 0.77, 0.83 and 0.86 at 100% depth dose, respectively. The RBE values of 30 MeV electrons were 0.85 at 95%, near the surface, and 0.89 at 68% depth doses. At 18% depth dose, a 0.78 RBE value was detected.