Dose response of the hazard ratio of the incidence of medulloblastoma in Ptch1+/– mice. Panels A–J: Ptch1+/– mice received γ-ray (panels A–E) or fast neutron (panels F–J) irradiation on embryonic day (E)14 or 17 or postnatal day (P)1, 4 or 10 and were observed until P500. Data for groups γ-ray irradiated on E14 (0.1 and 0.5 Gy), E17 (0.1 and 0.5 Gy), P1 (0.1 and 0.5 Gy), and P4 (0.1 and 0.5 Gy) are from previously published work (29 ). Hazard ratios (dots) are superimposed with linear dose response models (solid line). Error bars show 95% confidence intervals; in panel H, the arrow with a number in parentheses indicates the upper limit. *P < 0.05 and **P < 0.01 by Cox regression.