Department of Mathematics, Imperial College London, London SW7 2AZ, Division of Cancer, Imperial College London, Hammersmith Hospital, London W12 0NN and Department of Biomedical Engineering, Kings College London, St Thomas Hospital, London SE1 7EH, UK.|Department of Mathematics, Imperial College London, London SW7 2AZ, Division of Cancer, Imperial College London, Hammersmith Hospital, London W12 0NN and Department of Biomedical Engineering, Kings College London, St Thomas Hospital, London SE1 7EH, UK.|Department of Mathematics, Imperial College London, London SW7 2AZ, Division of Cancer, Imperial College London, Hammersmith Hospital, London W12 0NN and Department of Biomedical Engineering, Kings College London, St Thomas Hospital, London SE1 7EH, UK Department of Mathematics, Imperial College London, London SW7 2AZ, Division of Cancer, Imperial College London, Hammersmith Hospital, London W12 0NN and Department of Biomedical Engineering, Kings College London, St Thomas Hospital, London SE1 7EH, UK.