title: MRI-based biodistribution assessment of holmium-166 poly(L-lactic acid) microspheres after radioembolisation.
abstract: OBJECTIVE
  To demonstrate the feasibility of MRI-based assessment of the intrahepatic Ho-PLLA-MS biodistribution after radioembolisation in order to estimate the absorbed radiation dose.
  
  
  METHODS
  Fifteen patients were treated with holmium-166 ((166)Ho) poly(L-lactic acid)-loaded microspheres (Ho-PLLA-MS, mean 484 mg; range 408-593 mg) in a phase I study. Multi-echo gradient-echo MR images were acquired from which R (2) maps were constructed. The amount of Ho-PLLA-MS in the liver was determined by using the relaxivity r (2) of the Ho-PLLA-MS and compared with the administered amount. Quantitative single photon emission computed tomography (SPECT) was used for comparison with MRI regarding the whole liver absorbed radiation dose.
  
  
  RESULTS
  R (2) maps visualised the deposition of Ho-PLLA-MS with great detail. The mean total amount of Ho-PLLA-MS detected in the liver based on MRI was 431 mg (range 236-666 mg) or 89 ± 19 % of the delivered amount (correlation coefficient r = 0.7; P < 0.01). A good correlation was found between the whole liver mean absorbed radiation dose as assessed by MRI and SPECT (correlation coefficient r = 0.927; P < 0.001).
  
  
  CONCLUSIONS
  MRI-based dosimetry for holmium-166 radioembolisation is feasible. Biodistribution is visualised with great detail and quantitative measurements are possible.
authors.affiliation: Image Sciences Institute, University Medical Center Utrecht, Q S.459, PO Box 85500, 3508 GA Utrecht, The Netherlands. g.h.vandemaat@umcutrecht.nl
authors.forename: Gerrit H
authors.initials: GH
authors.lastname: van de Maat
authors.forename: Peter R
authors.initials: PR
authors.lastname: Seevinck
authors.forename: Mattijs
authors.initials: M
authors.lastname: Elschot
authors.forename: Maarten L J
authors.initials: ML
authors.lastname: Smits
authors.forename: Hendrik
authors.initials: H
authors.lastname: de Leeuw
authors.forename: Alfred D
authors.initials: AD
authors.lastname: van Het Schip
authors.forename: Maarten A D
authors.initials: MA
authors.lastname: Vente
authors.forename: Bernard A
authors.initials: BA
authors.lastname: Zonnenberg
authors.forename: Hugo W A M
authors.initials: HW
authors.lastname: de Jong
authors.forename: Marnix G E H
authors.initials: MG
authors.lastname: Lam
authors.forename: Max A
authors.initials: MA
authors.lastname: Viergever
authors.forename: Maurice A A J
authors.initials: MA
authors.lastname: van den Bosch
authors.forename: Johannes F W
authors.initials: JF
authors.lastname: Nijsen
authors.forename: Chris J G
authors.initials: CJ
authors.lastname: Bakker
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006695:Holmium / Q000032:analysis* / Q000627:therapeutic use*; D006801:Humans; D008099:Liver / Q000737:chemistry*; D008113:Liver Neoplasms / Q000737:chemistry* / Q000473:pathology / Q000532:radiotherapy*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008863:Microspheres; D008875:Middle Aged; D057054:Molecular Imaging / Q000379:methods; D009928:Organ Specificity; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000627:therapeutic use; D014018:Tissue Distribution
chemical_list: D019275:Radiopharmaceuticals; D006695:Holmium