Normal haematopoietic tissue and the malignant cells arising from it are very radiosensitive. Theoretically intensification of the conditioning therapy, particularly total body irradiation (TBI), prior to transplantation could increase tumour reduction leading to improved disease free survival rates for patients with poor risk disease. Targeted radiotherapy could allow treatment intensification without the toxicity to non-haematological tissues. In addition, the continuous, low dose rate delivered by the natural decay of a targeted radionuclide may have a greater destructive effect upon tumour cells than single dose or fractionated external beam radiation.