Quantitative biodistribution & kinetics of a new formulation of [Lu-177]-Octreotate

Objectives To report on the biodistribution and dosimetry of therapeutic [DOTA⁰,Tyr³]-octreotate (Auspep, AUS) with non-carrier added (nca) Lu-177 (ANSTO, AUS) ("nca-LuTATE") from gamma camera planar Whole Body (pWB) and quantitative SPECT (qSPECT) imaging of radionuclide therapy for neuro-endocrine tumours (NETs).

Methods Ten subjects received a total of >30 nca-LuTATE injections, each of approx. 8 GBq of Lu-177, following the EANM guidelines. All patients were given capecitabine for 5 days prior to treatment. The nca-LuTATE was synthesised using an Eckert & Ziegler PharmTracer system. pWB Lu-177 imaging (Siemens Symbia.T6, Intevo), including pre-treatment pWB transmission scanning for attenuation correction was performed. After administration of the nca-LuTATE, prior to voiding, pWB image estimates of total Lu-177 were made using the methods described in MIRD pamphlet 16. Patients were further scanned using pWB and qSPECT at approx. 4, 24 and 96 hrs post-injection to permit estimates of radiation dose using MIRD-based methodology (OLINDA-EXM).

Results pWB estimates of retained activity at the first imaging time point in 25 individual administrations of nca-LuTATE were accurate to within 6.6±4.6 %. Retention over time from pWB images resulted in t_½ of 2.1±0.6 hr for the fast and 58.1±7.2 hr for the slow component. Using qSPECT with OLINDA the average estimated radiation dose to renal tissue was 3.1±1.0 Gy per cycle. In 5 subjects who completed all 4 treatment cycles the average total dose to the kidneys for an individual was 12.0±3.9 Gy.

Conclusions The gamma camera can be used quantitatively to measure whole body retained Lu-177 as well as individual organ or tumour dosimetry with qSPECT. The retention and kidney dosimetry for nca-LuTATE has been shown to have an acceptable radiation safety profile. Compared to carrier-added Lu-177, the nca product has fewer radioactive waste management issues and less peptide needed. nca-LuTATE is an acceptable alternative to previous formulations.