Department of Electronic Engineering, City University of Hong Kong, Kowloon, Hong Kong.|Department of Clinical Oncology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong.|Centre for Mathematical Imaging and Vision and Department of Mathematics, Hong Kong Baptist University, Kowloon Tong, Hong Kong.|Department of Electronic Engineering, City University of Hong Kong, Kowloon, Hong Kong.|Laboratory for Experimental Oncology and Radiobiology, Center for Experimental and Molecular Medicine, Cancer Center Amsterdam and Academic Medical Center, Amsterdam, The Netherlands.