title: Preface.
authors.affiliation: Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, CH-1211 Geneva, Switzerland. Electronic address: habib.zaidi@hcuge.ch.
authors.forename: Habib
authors.initials: H
authors.lastname: Zaidi
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: kevin.teo@uphs.upenn.edu.
authors.forename: B Kevin
authors.initials: BK
authors.lastname: Teo