1. Department of Radiation Physics and Department of Medical and Health Sciences, Linköping University, SE-581 85 Linköping, Sweden
2. International Atomic Energy Agency, Dosimetry and Medical Radiation Physics Section, 1020 Vienna, Austria
3. Department of Medical and Health Sciences, Linköping University, SE-581 85 Linköping, Sweden
4. Department of Medical and Health Sciences, Linköping University, SE-581 85 Linköping, Sweden and Department of Medical Radiation Physics and Nuclear Medicine, Section for Radiotherapy Physics and Engineering, Karolinska University Hospital, SE-171 76 Stockholm, Sweden