Receptor-mediated radiotherapy with 90Y-DOTA-D-Phe1-Tyr3-octreotide

A newly developed somatostatin radioligand, DOTA-[D-Phe¹-Tyr³]-octreotide (DOTATOC), has been synthesised for therapeutic purposes, because of its stable and easy labelling with yttrium-90. The aim of this study was to determine the dosage, safety profile and therapeutic efficacy of ⁹⁰Y-DOTATOC in patients with cancers expressing somatostatin receptors. We recruited 30 patients with histologically confirmed cancer. The main inclusion criterion was the presence of somatostatin receptors as documented by ¹¹¹In-DOTATOC scintigraphy. ⁹⁰Y-DOTATOC was injected intravenously using a horizontal protocol: patients received equivalent-activity doses in each of three cycles over 6 months. The first six patients received 1.11 GBq per cycle and the four successive groups of six patients received doses increasing in 0.37-GBq steps. Toxicity was evaluated according to WHO criteria. No patient had acute or delayed adverse reactions up to 2.59 GBq ⁹⁰Y-DOTATOC per cycle (total 7.77 GBq). After a total dose of 3.33 GBq, one patient developed grade II renal toxicity 6 months later. The maximum tolerated dose per cycle has not yet been reached, although transient lymphocytopenia has been observed. Total injectable activity is limited by the fact that the maximum dose tolerated by the kidneys has been estimated at 20-25 Gy. Complete or partial tumour mass reduction occurred in 23% of patients; 64% had stable and 13% progressive disease. It is concluded that high activities of ⁹⁰Y-DOTATOC can be administered with a low risk of myelotoxicity, although the cumulative radiation dose to the kidneys is a limiting factor and requires careful evaluation. Objective therapeutic responses have been observed.