Nuclear Medicine's Clinical Pearls: The Case of Mistaken Linearity

Nuclear Pharmacists at Jubilant Radiopharma Radiopharmacies Division, frequently receive calls from customers seeking guidance on a variety of clinical scenarios or answers to other questions that they encounter while performing their daily work. Thanks to our Pharmacists’ specialized knowledge and expertise, they are often able to offer solutions that save the customer time and money. The following describes a clinical scenario involving linearity testing that the Jubilant Radiopharma Radiopharmacies Division-Myrtle Beach Pharmacy, led by Dr. Angela Hitchcock, helped a customer resolve.


Recently, my team at Jubilant Radiopharma Radiopharmacies Division-Myrtle Beach helped a customer that was having problems with their linearity testing. The customer called the Pharmacy to explain that they were performing their quarterly linearity testing, using the attenuation sleeves method, when they discovered one of the tests (the middle sleeve) was out of range. As a result, their linearity failed. Not knowing where else to turn, the customer then asked if the pharmacy could loan them a new dose calibrator so they could send theirs off for repair.  


Since the customer was performing the test a week in advance, there was time to react before the quarterly linearity testing deadline. As a first step, we asked them to send us their data so that we could confirm that the linearity had indeed failed. We then asked where the calibration numbers assigned to their tubes came from and if the tubes had been damaged recently. The customer reported there had been no damage to the tubes, but indicated they were unfamiliar with how the calibration numbers were assigned.

Next, we discussed the need to perform a time-decay linearity; If that passed, we would be able to reassign calibration numbers to the tubes. Our customer was unfamiliar with this process, but, despite being located a few hours away, we helped them work through it remotely.

We then sent them the activity and had them call us at specific times, writing down the time and the activity amount upon receiving each call. In conjunction with this, the customer initially performed readings within five minutes of all tube shieldings, obtained the activity results and sent us those numbers as well. After three days of collaboration, we had the activity decayed down per their RAM application and processed the results.

Using the time-decay process, we showed that their dose calibrator passed the linearity test and could accurately measure activities within the tested ranges. We also assigned new calibration factor numbers to all of their tubes based on their new readings, which were substantiated by the fact that the time-decay linearity passed.


Not only did the customer eliminate unnecessary costs associated with sending their dose calibrator off for “repair”, they also saved time by not having to perform new geometries, linearities and constancies on a loaner DC.  

While that made them happy, this effort was equally rewarding to our Pharmacy Team. We enjoyed working alongside our colleagues in nuclear medicine to help solve the problem and to educate them on linearity procedures and methods.

Disclaimer: Although the presentation of this clinical scenario is for informational use only, it is from actual personal pharmacy experience and is not a replacement for training, experience, continuing education or studying the latest literature. Healthcare professionals should use educated clinical judgment first and foremost when making decisions regarding drug and procedural suggestions.