Establishment of transfer standard for holmium-166-DOTMP

The measurement of 166Ho, both as a chloride solution and as [166Ho]-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylenephoonic acid (DOTMP), was examined for four models of radionuclide calibrators: Capintec CRC-35R (two chambers), Capintec 712MX, AtomLab 100 (two chambers), and a Capintec CRC-12. Holmium-166 chloride was measured as 16 ml in 20-ml glass dose vials. Diagnostic imaging level [166Ho]DOTMP solutions, nominally 400 MBq g−1, were measured as 12 ml in 20-ml dose vials. Finally, therapeutic level [166Ho]DOTMP solutions, nominally 9 GBq g−1, were measured as aliquots of 100–500 μl in sealed plastic vials of 10-ml saline. Single calibration factors for each instrument manufacturer are recommended for 12–16-ml of either solution in 20-ml glass dose vials, (673±9)×10 and 72.7±0.7, for the Capintec and AtomLab models, respectively. Calibration factors recommended for the therapeutic dose geometry are (706±6)×10 and 68.7±1.3, for the Capintec and AtomLab models, respectively. The calibration factors recommended for an NIST 5-ml ampoule are (686±5)×10 and 70.9±0.4 for the Capintec and AtomLab models, respectively.