Dose dependent growth delay induced by 200 kV X-ray treatment. Tumour growth curves measured after irradiation with 200 kV X-rays (0 – 13.2 Gy) and for the untreated control (black curve, partly covered by the 0 Gy line). The relative volumes in dependence on time are determined on basis of the volumes at the start of the treatment. The numbers of animals allocated to the different groups are given in brackets; the measured data are given as mean value ± SEM of all animals in this particular group. The tumour growth delay relative to the untreated control was significant (*p < 0.05, ***p < 0.001) for doses higher than 7.6 Gy for the 10fold volume increase and for doses higher than 3.8 Gy at higher volume increases, respectively.