title: Human radiation dosimetry of [11C]MeAIB, a new tracer for imaging of system A amino acid transport.
abstract: OBJECTIVE
  [N-methyl-11C]alpha-methylaminoisobutyric acid ([11C]MeAIB) is a promising positron emission tomography (PET) tracer for imaging hormonally regulated system A amino acid transport. Uptake of [11C]MeAIB is totally specific for amino acid transport since [11C]MeAIB is metabolically stable both extra- and intracellularly. The aim of this study was to measure cumulated radioactivity in different organs and estimate the absorbed radiation doses to humans with the Medical Internal Radiation Dosimetry (MIRD) method.
  
  
  METHODS
  Radiation absorbed doses were calculated from PET images for 25 volunteers. Dynamic acquisition data were obtained for the thoracic, abdominal, femoral and head and neck regions. The median dose of intravenously injected [11C]MeAIB was 422+/-35 MBq, with a range of 295-493 MBq. After PET imaging the radioactivity in voided urine was measured. Experimental human data were used for residence time estimates. Radiation doses were calculated with commonly used software.
  
  
  RESULTS
  The effective dose for a 70-kg adult was 0.004 mSv/MBq, corresponding to a 1.72 mSv effective dose from the PET study with injection of 430 MBq [11C]MeAIB. The highest absorbed doses were in the pancreas (0.018 mGy/MBq), kidneys (0.017 mGy/MBq), intestine (0.014 mGy/MBq), liver (0.008 mGy/MBq) and stomach (0.005 mGy/MBq). Only 0.57% of injected activity was excreted to urine within 1 h after injection.
  
  
  CONCLUSIONS
  Biodistribution of [11C]MeAIB in the abdominal region reflected the high activity of the transportation of amino acids via system A and these organs also had the highest radiation doses. An effective dose of 0.004 mSv/MBq is fully justified when [11C]MeAIB PET is performed to study system A activity in vivo.
authors.affiliation: Turku PET Centre, Turku University Hospital, P.O. Box 52, 20521, Turku, Finland. tuula.tolvanen@tyks.fi
authors.forename: Tuula
authors.initials: T
authors.lastname: Tolvanen
authors.forename: Kjell
authors.initials: K
authors.lastname: Någren
authors.forename: Meixiang
authors.initials: M
authors.lastname: Yu
authors.forename: Eija
authors.initials: E
authors.lastname: Sutinen
authors.forename: Katja
authors.initials: K
authors.lastname: Havu-Aurén
authors.forename: Sirkku
authors.initials: S
authors.lastname: Jyrkkiö
authors.forename: Markku
authors.initials: M
authors.lastname: Asola
authors.forename: Eira
authors.initials: E
authors.lastname: Kotoneva
authors.forename: Pirjo
authors.initials: P
authors.lastname: Nuutila
authors.forename: Heikki
authors.initials: H
authors.lastname: Minn
mesh_terms: D026924:Amino Acid Transport System A / Q000378:metabolism*; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D015336:Molecular Probe Techniques; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D009928:Organ Specificity; D011829:Radiation Dosage; D011865:Radioisotope Dilution Technique; D011874:Radiometry / Q000379:methods*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D014018:Tissue Distribution; D015091:beta-Alanine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
chemical_list: D026924:Amino Acid Transport System A; D002250:Carbon Radioisotopes; D019275:Radiopharmaceuticals; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine