The aim of this paper was to describe the optimized labeling protocol and quality control measures used in the production of [(90)Y]DOTATOC, starting from three different radioactivity levels to treat one, two, or three patients per therapeutic session. We investigated three different starting radioactivity levels. For the low radioactivity preparation we used 5138±280 MBq of [Y] isotope, for the medium radioactivity preparation we used 8893±900 MBq, and for the high radioactivity preparation we used 11250±715 MBq. The radiochemical purity levels for the low radioactivity preparation, medium radioactivity preparation, and high radioactivity preparation were 99.95±0.09, 99.84±0.34, and 99.84±0.53%, respectively, and the radiochemical yields of the labeling procedures were 77.52±1.28, 75.53±3.72, and 78.00±3.20%, respectively. Media fill validation of the process was performed, and the parameters of pH, bacterial endotoxins, sterility, and osmolality were tested at process control. All radiopharmaceutical preparations satisfied the predetermined specifications fixed in our protocol regardless of the starting radioactivity level. The validation of the method guaranteed the safety and quality of the final products, contributing to providing the basis for constructing an informative and successful clinical trial.