1. Radiation Biophysics Laboratory, Department of Physics “E. Pancini”, University Federico II, 80126 Naples, Italy
2. Istituto Nazionale di Fisica Nucleare, INFN, Naples Section, 80126 Naples, Italy
3. Department of Physics, University of Pavia, 27100 Pavia, Italy
4. Istituto Nazionale di Fisica Nucleare, INFN, Pavia Section, 27100 Pavia, Italy
5. Department of Clinical Surgical Sciences, University of Pavia, 27100 Pavia, Italy