Glioblastoma multiforme (GBM) cells are more radiosensitive to125I seed irradiation than X-ray. (A) Representative pictures of the colony-formation ability of U251 (upper panel) and U87 (lower panel) cells exposed to 125I seed and X-ray at various doses for 14 days. The survival fraction of the colony-formation assay was fitted by the single-hit multi-target theory formula. (B) The cell viability of U251 (left panel) and U87 (right panel) cells treated with irradiation was examined by MTT assay. (C) Proliferation of U251 (upper panel) and U87 (lower panel) cells was measured by EdU assay. Significant differences between the 125I seed and X-ray groups under the same dose are indicated by *P <0.05 and **P < 0.01.