New rubidium-82 generator efficiency improves over time

Introduction: PET myocardial perfusion imaging (MPI) with rubidium-82 (Rb-82) is being more widely adopted due to superior diagnostic accuracy and availability without the need for an onsite cyclotron. Rb-82 is obtained by eluting a Sr-82/Rb-82 generator via an automated system, creating 82RbCl for direct patient injection. Obtaining maximal Rb-82 activity daily over several weeks extends the useful life of the generator for clinical PET imaging. We evaluated the efficiency of a commercial Rb-82 generator and elution system for delivery of activity over its lifecycle.

Methods: The efficiency of a commercial Rb-82 generator model (RUBY-FILL™, Jubilant DraxImage Inc.), used in conjunction with its partner elution system was evaluated over a 3.5-year period. An automated daily quality control (QC) procedure was performed on each day of patient use and the Rb-82 yield as measured by the onboard dose calibrator of the elution system was documented. Cumulative volume eluted through the generator was also recorded. Generator efficiency was calculated as the ratio of the daily Rb-82 yield to the theoretically expected Rb-82 activity based on the initial 100 mCi (3700 MBq) activity of the parent Sr-82 loaded onto the generator column and its radioactive decay. Efficiency was determined at installation of the generator into the elution system and at the end of each subsequent week until expiry at 8 weeks.

Results: At generator installation (1 ± 3 days after calibration), average efficiency over the 16 generators tested was determined to be 91 ± 6 %, with a maximal available activity of 80 ± 7 mCi. Generator efficiency increased over the weeks of use. Near expiry (day 52 ± 11) efficiency was significantly increased to 97 ± 7 % (p = 0.0005 as compared to installation), corresponding to a maximal available activity of 21 ± 2 mCi. This represents an overall improvement of 6% from generator installation to expiry. The increased efficiency may be due to changes in the fluid dynamics of the tin-oxide column elution profile allowing the full Rb-82 activity to be flushed off of the column after 8 weeks of use. The total eluted volume over the 8-week lifecycle was consistent for a subset of generators with this information available (N=6): 11.3 ± 0.2 L, which is well below the allowed 30 L limit. These results indicate that the daily Rb-82 activity available for elution approaches the maximum theoretical yield over time and the total eluted volume remains within allowable limits, thus extending the useful life of the generator for clinical PET MPI imaging. Conclusion: The efficiency of the RUBY-FILL™ Rb-82 generator improves over time, allowing maximal Rb-82 activity (21 mCi) to be administered for clinical PET perfusion imaging at the end of its 8-week shelf-life. Research support: Clinical trial #NCT02117284 supported by Jubilant DraxImage Inc.