Yttrium-90 and Rhenium-188 Radiopharmaceuticals for Radionuclide Therapy

adionuclidic purity of the 90 Y solution, the ‘BARC technique’ was also used.
This method was a combination of solvent EPC [10.20] wherein Whatman No. 1
(18 cm × 2 cm) paper chromatographic strips impregnated with KSM-17 at the
point of spotting were used. On development with normal saline, 90 Sr moved to
the solvent front, while 90 Y was retained at the point of spotting. The activity at
the solvent front was estimated by cutting the chromatograms into 1 cm strips and
measuring radioactivity in a dose calibrator. Radionuclidic purity was calculated
as a percentage of the total activity spotted.
10.4.3. Results and discussion
10.4.3.1. Electrochemical separation of 90 Y
Although there are different methods of separation of 90 Y from the parent
radionuclide 90 Sr reported in the literature [10.19], the 90 Sr/ 90 Y generator used an
electrochemical method for separation of 90 Y. The electrolysis was carried out in
an electrolytic quartz cell, prepared in the Laboratory for Radioisotopes, Vinča
Institute of Nuclear Sciences (see Fig. 10.15(a)), as potentiostatic electrolysis with
potential –2.500 ± 0.055 V with respect to the SCE. During the first electrolysis,
the current was increased from 730 to 745 mA. The electrolytic potential at the
platinum cathode was stable during the electrolysis, but could not be maintained
at –2.50 V. It fell to –2.39 V, but was within the accepted limits of ± 0.2% plus
5 mV, in constant voltage mode. The pH was adjusted to 2.7 ± 0.2.
The second electrolysis was accomplished with a stable potential of –2.50 V
on the platinum cathode and a constant current of 100 mA during the electrolysis.
The solution was warmed up during electrolysis, and hence subsequent cooling
of the electrolysis cell was necessary. Separation of H 2 gas was also detected
(see Fig. 10.15(b)) and, therefore, stirring during the process was not required.
These conditions ensured that the deposition yield was >90%.
10.4.3.2. Quality control of 90 Y
Yttrium-90 exists in secular equilibrium with its parent isotope 90 Sr, which
is a product of the fission reaction. Many impurities must be removed, and pure
90 Y has to be converted into an appropriate chemical form for application in
medicine therapy. Radioactive 90 Sr, as 90 Sr(NO 3 ) in equilibrium with 90 Y in 1M
HNO 3 from POLATOM, had a high radionuclidic purity (>99.5%), as well as a
high RCP. Strontium-90 breakthrough was the major problem often encountered
with the 90 Sr/ 90 Y generator. Because 90 Sr is a bone seeker and the upper limit of
201