title: In vivo dosimetry based on SPECT and MR imaging of 166Ho-microspheres for treatment of liver malignancies.
abstract: (166)Ho-poly(l-lactic acid) microspheres allow for quantitative imaging with MR imaging or SPECT for microsphere biodistribution assessment after radioembolization. The purpose of this study was to evaluate SPECT- and MR imaging-based dosimetry in the first patients treated with (166)Ho radioembolization.
  
  
  METHODS
  Fifteen patients with unresectable, chemorefractory liver metastases of any origin were enrolled in this phase 1 study and were treated with (166)Ho radioembolization according to a dose escalation protocol (20-80 Gy). The contours of all liver segments and all discernible tumors were manually delineated on T2-weighted posttreatment MR images and registered to the posttreatment SPECT images (n = 9) or SPECT/CT images (n = 6) and MR imaging-based R2* maps (n = 14). Dosimetry was based on SPECT (n = 15) and MR imaging (n = 9) for all volumes of interest, tumor-to-nontumor (T/N) activity concentration ratios were calculated, and correlation and agreement of MR imaging- and SPECT-based measurements were evaluated.
  
  
  RESULTS
  The median overall T/N ratio was 1.4 based on SPECT (range, 0.9-2.8) and 1.4 based on MR imaging (range, 1.1-3.1). In 6 of 15 patients (40%), all tumors had received an activity concentration equal to or higher than the normal liver (T/N ratio ≥ 1). Analysis of SPECT and MR imaging measurements for dose to liver segments yielded a high correlation (R(2) = 0.91) and a moderate agreement (mean bias, 3.7 Gy; 95% limits of agreement, -11.2 to 18.7).
  
  
  CONCLUSIONS
  With the use of (166)Ho-microspheres, in vivo dosimetry is feasible on the basis of both SPECT and MR imaging, which enables personalized treatment by selective targeting of inadequately treated tumors.
authors.affiliation: Department of Radiology and Nuclear Medicine, University Medical Center Utrecht, Utrecht, The Netherlands; and.
authors.forename: Maarten L J
authors.initials: ML
authors.lastname: Smits
authors.forename: Mattijs
authors.initials: M
authors.lastname: Elschot
authors.forename: Maurice A A J
authors.initials: MA
authors.lastname: van den Bosch
authors.forename: Gerrit H
authors.initials: GH
authors.lastname: van de Maat
authors.forename: Alfred D
authors.initials: AD
authors.lastname: van het Schip
authors.forename: Bernard A
authors.initials: BA
authors.lastname: Zonnenberg
authors.forename: Peter R
authors.initials: PR
authors.lastname: Seevinck
authors.forename: Helena M
authors.initials: HM
authors.lastname: Verkooijen
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Bakker
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: Johannes F W
authors.initials: JF
authors.lastname: Nijsen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004621:Embolization, Therapeutic / Q000009:adverse effects; D005260:Female; D006695:Holmium / Q000009:adverse effects / Q000737:chemistry* / Q000627:therapeutic use*; D006801:Humans; D019344:Lactic Acid / Q000737:chemistry; D008099:Liver / Q000528:radiation effects; D008113:Liver Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000628:therapy*; D008279:Magnetic Resonance Imaging; D008297:Male; D008863:Microspheres; D008875:Middle Aged; D064847:Multimodal Imaging; D011091:Polyesters; D011108:Polymers / Q000737:chemistry; D011874:Radiometry; D012449:Safety; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide); D006695:Holmium
keywords: MRI; SIRT; SPECT; holmium; radioembolization