Fig. 2.

Hypofractionated irradiation induces predominantly apoptosis in HNSCC cells. a Timeline shows the treatment of the HNSCC cells starting on day 3 by seeding the cells and incubating them for the following 3 days at standard culture conditions. The tumor cells were irradiated with 5 Gy on day 4 and 5 (2 × 5Gy). The control group (mock-treated) was left untreated (0 Gy). On day 6, 24 h after the last irradiation, cell death analysis of the tumor cells was performed by FITC-labeled AnnexinA5 (AxV) and propidium iodide (PI) staining. Cell death is represented by the necrotic and apoptotic cell population of the HPV-negative HNSCC cell line cal33 (b) and the HPV-positive HNSCC cell line UD2 (c). Necrotic cells were defined as PI+, apoptotic cells as AxV+ and PI−. Statistical analysis was carried out with the Mann–Whitney U test. Significance is indicated as: * p < 0.05. Data are presented as mean with SD