1. Department of Mathematical Sciences; University of Bath; Bath BA2 7AY UK
2. Institute for Medical Biometry and Statistics; University of Freiburg; Stefan-Meier-Str. 26 79104 Freiburg Germany
3. Freiburg Center for Data Analysis and Modeling; University of Freiburg; Eckerstr. 1 79104 Freiburg Germany
4. Section Clinical Studies, Department of Radiation Oncology; University Hospital Freiburg; Hugstetter Strasse 55 79106 Freiburg Germany