Molecular radiotherapy (MRT) is a systemic use of radiolabelled vectors (radiopharmaceuticals) for the treatment of benign and malignant tumours. A radiopharmaceutical consisting of a radionuclide linked to a targeting molecule binds specifically to tumours to selectively irradiate the tumour cells while sparing healthy tissues. In clinical practice, patients are most often administered fixed activity (under the “radioactive chemotherapy” paradigm) [1]. However, significant variability in tumour uptake and radioactivity clearance from patient to patient can be observed.