1 Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, UK; Department of Oncology, Guy's and St Thomas' NHS Foundation Trust, London, UK. Electronic address: ajay.aggarwal@lshtm.ac.uk.
2 Department of Radiation Oncology, Ghent University Hospital & Ghent University, Ghent, Belgium.
3 Institute of Cancer Policy, King's College London, London, UK.
4 Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, UK.