Radiosensitivity assay. Clonogenic survival assays with primary skin were performed as described in Noordzij et al., Blood 2003 [5
]. In short, primary skin fibroblasts in exponential growth were trypsinized, and 1000–2,000 cells (10,000–20,000 cells for the highest doses) were seeded into 10 cm plastic dishes (2 dishes per dose) and irradiated at room temperature with 0, 1,2,4 or 6 Gy. After 12–14 days, the cells were rinsed with 0.9% NaCl and stained with 0.25% methylene blue for survival assessment. Two independent survival experiments were performed.