The radiobiological effects of He, C and Ne ions as a function of LET on various glioblastoma cell lines

The effects of the charged ion species He-4, C-12 and Ne-20 on glioblastoma multiforme (GBM) T98G, U87 and LN18 cell lines were compared with the effects of 200 kVp X-rays (1.7 keV/pm). These cell lines have different genetic profiles. Individual GBM relative biological effectiveness (RBE) was estimated in two ways: the RBE10 at 10% survival fraction and the RBE2 Gy after 2 Gy doses. The linear quadratic model radiosensitivity parameters alpha and beta and the alpha/beta ratio of each ion type were determined as a function of LET. Mono-energetic He-4, C-12 and Ne-20 ions were generated by the Heavy Ion Medical Accelerator at the National Institute of Radiological Sciences in Chiba, Japan. Colony-formation assays were used to evaluate the survival fractions. The LET of the various ions used ranged from 2.3 to 100 keV/mu m (covering the depth-dose plateau region to clinically relevant LET at the Bragg peak). For U87 and LN18, the RBE(10 )increased with LET and peaked at 85 keV/mu m, whereas T98G peaked at 100 keV/mu m. All three GBM alpha parameters peaked at 100 keV/mu m. There is a statistically significant difference between the three GBM RBE10 values, except at 100 keV/pm (P < 0.01), and a statistically significant difference between the a values of the GBM cell lines, except at 85 and 100 keV/mu m. The biological response varied depending on the GBM cell lines and on the ions used.