Pre-therapeutic dosimetry and biodistribution of 86Y-DOTA-Phe1-Tyr3-octreotide versus 111In-pentetreotide in patients with advanced neuroendocrine tumours.

PURPOSE: For the internal radiotherapy of neuroendocrine tumours, the somatostatin analogue DOTATOC labelled with 90Y is frequently used [90Y-DOTA-Phe1-Tyr3)-octreotide (SMT487-OctreoTher)]. Radiation exposure to the kidneys is critical in this therapy as it may result in renal failure. The aim of this study was to compare cumulative organ and tumour doses based upon dosimetric data acquired with the chemically identical 86Y-DOTA-Phe1-Tyr3-octreotide (considered as the gold standard) and the commercially available 111In-pentetreotide. METHODS: The cumulative organ and tumour doses for the therapeutic administration of 13.32 GBq 90Y-DOTA-Phe1-Tyr3-octreotide (three cycles, each of 4.44 GBq) were estimated based on the MIRD concept (MIRDOSE 3.1 and IMEDOSE). Patients with a cumulative kidney dose exceeding 27 Gy had to be excluded from subsequent therapy with 90Y-DOTA-Phe1-Tyr3-octreotide, in accordance with the directives of the German radiation protection authorities. RESULTS: The range of doses (mGy/MBq 90Y-DOTA-Phe1-Tyr3-octreotide) for kidneys, spleen, liver and tumour masses was 0.6-2.8, 1.5-4.2, 0.3-1.3 and 2.1-29.5 (86Y-DOTA-Phe1-Tyr3-octreotide), respectively, versus 1.3-3.0, 1.8-4.4, 0.2-0.8 and 1.4-19.7 (111In-pentetreotide), with wide inter-subject variability. Despite renal protection with amino acid infusions, estimated cumulative kidney doses in two patients exceeded 27 Gy. CONCLUSION: Compared with 86Y-DOTA-Phe1-Tyr3-octreotide, dosimetry with 111In-pentetreotide overestimated doses to kidneys and spleen, whereas the radiation dose to the tumour-free liver was underestimated. However, both dosimetric approaches detected the two patients with an exceptionally high radiation burden to the kidneys that carried a potential risk of renal failure following radionuclide therapy.