(a) PET scans of mice HD-10 (large tumour, high uptake), HD-07 (small tumour, high uptake) and HD-18 (medium-sized tumour, low uptake), demonstrating intertumoural uptake heterogeneity. (b) Determination of intratumoural DOX concentrations based on 89Zr-NRep %ID per g uptake values. Only the data for animals injected with 20 mg kg−1 are shown. The data corresponding to the 10 mg kg−1 group are shown in Supplementary Fig. 5a. (c) Individual non-invasively determined intratumoural DOX concentrations for mice receiving either 20 mg kg−1 Doxil (N=20) or 10 mg kg−1 Doxil (N=10). Labelled red arrows in b and c indicate data points for mice HD-10, HD-07 and HD-18. Their PET scans are shown in a.