1. Group of Medical Physics and Biomathematics, Instituto de Investigación Sanitaria de Santiago (IDIS), 15706 Santiago de Compostela, Spain
2. Department of Medical Physics, Complexo Hospitalario Universitario de Santiago de Compostela, 15706 Santiago de Compostela, Spain
3. Department of Applied Mathematics, Universidade de Santiago de Compostela, 15705 Santiago de Compostela, Spain
4. Department of Radiation Oncology, Complexo Hospitalario Universitario de Santiago de Compostela, 15706 Santiago de Compostela, Spain
5. Institute of Physics, Pontificia Universidad Católica de Chile, Santiago de Chile 7820436, Chile