Molar activity - The keystone in ¹¹C-radiochemistry: An explorative study using the gas phase method

Area of Science:

• Radiochemistry
• Radiopharmacy
• Nuclear Medicine

Background:

• Radiochemists/radiopharmacists require high specific/molar activity for radiopharmaceuticals to prevent receptor saturation and adverse effects in PET imaging.
• Low molar activity in carbon-11 (¹¹C)-labeled radiotracers is a common challenge, often due to unidentified carbon-12 (¹²C) contamination.

Purpose of the Study:

• To analyze and quantify diverse ¹²C contaminations impacting molar activity in routine radiopharmaceutical production.
• To identify the origins of ¹²C contamination in commercial synthesis modules used for PET tracers.

Main Methods:

• Analysis and quantification of ¹²C contaminations across >450 syntheses of six PET tracers.
• Use of [¹¹C]CO₂ or [¹¹C]CH₃I generated via gas phase method in a commercial synthesizer.
• Performance of non-radioactive syntheses to pinpoint sources of ¹²C contamination.

Main Results:

• Contributions to low molar activity were categorized into technical parameters (e.g., gas/reagent quality), inter/intralaboratory parameters (e.g., maintenance, module load), and interoperator parameters (e.g., handling).

Conclusions:

• The study enhances understanding of factors contributing to carbon load in synthesis modules.
• This knowledge facilitates the consistent maintenance of high molar activity for ¹¹C-labeled radiopharmaceuticals.