Human dosimetry for the 5-HT6 PET ligand [11C]GSK215083

Objectives [¹¹C]GSK215083 is a new 5-HT6 antagonist PET tracer (Parker, 2008). The aim of this study was to collect whole body human data to calculate the radiation dose from this tracer.

Methods Five healthy subjects (3 males and 2 females, mean age 25.6 years SD 4.93) underwent wholebody PET scans (with CT measured attenuation correction) on a Siemens-Biograph HiRez XVI PET camera system, following a single bolus injection of 330-370 MBq of [¹¹C]GSK215083. Emission data was acquired for up to 120 minutes, as a series of consecutive overlapping bed positions, from the top of head to mid thigh. Tissues exhibiting above background uptake were identified and regions of interest (ROIs) were delineated on emission images. For each ROI residence times were determined and entered into the dose estimation software OLINDA to calculate the radiation dose.

Results On preliminary analysis the following ROIs exhibited accumulation of [¹¹C]GSK215083 above background.

Results Effective Dose (ED) values ranged from 5-8 µSv/MBq, with female subjects tending to have a higher ED than males.

Conclusions The estimated ED was approximately 7 µSv/MBq, consistent with data from other neuroreceptor ligands labelled with carbon-11. Analysis utilising ROIs defined on CT images is ongoing, this is likely to improve upon the accuracy of the ED obtained using PET alone. In addition data from a third female subject has been collected.