 In light of the recent guidelines, the proposed new clinical protocol will include blood samples taken from the patient during the in-patient stay. On the day of treatment, blood samples will be taken at 2h and 6h after radioiodine administration, at the same time as the clearance measurements. Thereafter, a blood sample will be taken from the patient once per day, at the same time as one of the clearance measurements. In addition, a further blood sample will be taken when the patient attends for whole-body and SPECTCT scans. These blood samples will then be analysed in the laboratory using standard radiation measurement procedures to determine the blood dose according to the European guidelines. 