Container-content interactions tests for automated dispensing of radiopharmaceuticals : who’s gonna stick to it?

Introduction
In nuclear medecine, when dispensing, ready-to-use radiopharmaceuticals (RPs) automatic dispensing systems offer technical and radiation protection advantages.
These systems operate with captive consumables and are mainly used for [^18F]FDG, [^18F]Fcholine, and [^18F]Fdopa dispensing. However, their use for less common RPs is still poorly documented.

Aim
The aim of this study is to evaluate the container-content interactions between the Karl100 dispensing system (Tema Sinergie) and three fluorinated RPs.

Materials & Methods
Karl100 requires the use of a daily kit composed of : 1 collecting vial, 1 activimeter vial, a 0.22 µm filter, 3-way valves and tubings. The loading of the MRP into the kit and its dispensing in syringes were tested, then administration to patients was simulated in a vial through a 0.22 µm filter perfuser.
Daily kit and infusion line were then cut into several parts, whose radioactivity was measured in a calibrated activimeter. The RPs tested were [^18F]piflufolastat (PFF), [^18F]florbebetabene (FBB) and [^18F]fluoroestradiol (FES).

Results
A total of 5 loads were performed, 11 syringes dispensed and 6 administered.
For PFF, when loaded into the automate: 0.2% of initial activity was found on the filter and 0.5% on the rest of the kit. Three syringes were dispensed with a dose accuracy (Da) of ‑4.8%. The « administered » activity was 96.7% with a 0.1% retention on the perfuser line filter.
For FBB, a total adsorption on the kit was observed at the first test: the RP could not be loaded in the collecting vial and no syringe could be dispensed. A second test was performed by adding ethanol to the RP vial before loading and then for the flushing process. Filter adsorption decreased to 21.5% but that of the kit was 41.5%. Three syringes were dispensed with a Da of -87.3% but no administration could be performed. The third test simulated the administration of a manually withdrawn dose : « administered » activity was 2.1% with 63.7% retention on the infusion filter. The fourth test consisted of loading the RP by by-passing the kit filter: adsorption on the kit was 38.8%. Three syringes were dispensed wih a Da of -27.3%. The « administered » activity recovery was 82.0% with a filterless perfuser and 5.5% with a filter. The residual activity in the syringe was 12.5% after administration.
For FES, 70.6% of RP was loaded with 40.5% adsorption on the filter and 23.4% on the kit observed. The Da was -71.4%.

Discussion
Material adsorption, whether it comes from filters, kits tubing or perfusion line, greatly depend on RPs physical and chemical properties. Preliminary tests are therefore essential before any clinical use, as some RPs are not currently compatible with automatic dispensing on Karl100, particulary lipophilic ones.

Key words: radiopharmaceuticals, adsorption, automated dispensing

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