Sr-82 Breakthrough Above the Limit on a Rubidium-82 Generator
A hospital operates a Sr-82/Rb-82 generator for cardiac PET. The generator is 42 days old and has eluted 28 liters. On Monday morning, the technologist performs the required Sr-82 breakthrough test on the first elution. The dose calibrator reading for Sr-82 is 0.031 kBq per MBq of Rb-82, and the Sr-85 result is 0.09 kBq per MBq. The department's written limit is 0.02 kBq per MBq for Sr-82 and 0.2 kBq per MBq for Sr-85. A patient with chest pain is scheduled for a Rubidium-82 perfusion study in 30 minutes. The technologist wants to repeat the test after flushing the generator with 50 mL of saline and then proceed if the repeat is below the limit.
1. Interpret the breakthrough results. Can the generator be used for the scheduled patient?
Read the worked answer
The Sr-82 result is 0.031 kBq per MBq, which exceeds the department's limit of 0.02 kBq per MBq. The Sr-85 result is 0.09 kBq per MBq, which is below its 0.2 kBq per MBq limit. Because the Sr-82 breakthrough exceeds the limit, the generator must not be used for patient elutions. The scheduled Rubidium-82 perfusion study should not proceed from this generator.
A single flush and retest is not an acceptable way to return an out-of-limit generator to service. Sr-82 has a 25.5-day half-life, so it will not decay quickly, and flushing does not reliably correct a failed breakthrough test. The generator should be removed from clinical service and managed according to the manufacturer's instructions and the facility's written procedures.
2. What regulatory, safety, and documentation actions should follow?
Read the worked answer
The generator should be immediately labeled out of service and physically secured or disconnected so that it cannot be eluted for patients. The authorized user and radiation safety officer should be notified. The result should be documented in the generator log, including the date, elution number, measured Sr-82 and Sr-85 activities, the limit, and the action taken. The manufacturer should be contacted, and the generator should be returned or disposed of according to the license and manufacturer's instructions.
Prior elutions should be reviewed to determine whether earlier breakthrough results were approaching the limit. If a patient received an elution that exceeded the limit, the authorized user should assess the estimated patient dose and follow facility policy and regulatory reporting requirements. The department should also review why the scheduled patient was still booked after an out-of-limit result and reinforce the stop-use policy.