title: Determination of Skeletal Tumor Burden on 18F-Fluoride PET/CT.
abstract: The purpose of this study was to define a method to assess skeletal tumor burden with 18F-labeled sodium fluoride PET/CT (18F-fluoride PET/CT) and evaluate the reproducibility of these measurements.
  
  
  METHODS
  Ninety-eight consecutive patients (90 men; mean age±SD, 65.7±14.2 y) underwent 158 18F-fluoride PET/CT scans for evaluation of skeletal metastatic disease. In order to determine the mean normal bone SUV, initially a 1-cm spheric volume of interest (VOI) was placed over 5 bone sites: T12, L5, sacrum, right iliac bone, and right femur. For each patient, the mean SUVmax for all sites was generated. Afterward, a threshold value of normal bone uptake was established. Subsequently, skeletal tumor burden was determined by generating volumetric data using a whole-body segmentation method. Any SUVmax below the normal threshold was excluded from analysis, as were VOIs not related to metastatic disease. Statistics for the remaining VOIs were then generated and defined as the skeletal metastatic tumor burden by 2 parameters: total lesion fluoride uptake above an SUVmax of 10 (TLF10) and fluoride tumor volume above an SUVmax of 10 (FTV10). TLF10 and FTV10 reproducibility was determined using 2 independent and experienced PET/CT interpreters analyzing a subset of 13 18F-fluoride PET/CT scans.
  
  
  RESULTS
  Mean (±SD) normal bone SUVmax was 6.62±1.55 for T12, 6.11±1.73 for L5, 4.59±1.74 for sacrum, 5.39±1.72 for right iliac bone, and 3.90±1.57 for right femur. The mean normal SUVmax for all 543 sites was 5.32±0.99. On the basis of these values, an SUVmax threshold of 10 was chosen to exclude normal bone from the volumetric calculations. Semiautomated measurements of TLF10 and FTV10 exhibited high interobserver reproducibility, within ±0.77% and ±3.62% of the interinterpreter average for TLF10 and FTV10, respectively.
  
  
  CONCLUSIONS
  Determination of skeletal tumor burden with 18F-fluoride PET/CT is feasible and highly reproducible. Using an SUVmax threshold of 10 excludes nearly all normal bone activity from volumetric calculations.
authors.affiliation: Department of Nuclear Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Rohren
authors.affiliation: Department of Nuclear Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas Division of Nuclear Medicine, University of Campinas (UNICAMP), Campinas, Brazil elba.etchebehere@gmail.com.
authors.forename: Elba C
authors.initials: EC
authors.lastname: Etchebehere
authors.affiliation: Department of Genitourinary Medical Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas; and.
authors.forename: John C
authors.initials: JC
authors.lastname: Araujo
authors.affiliation: Department of Biostatistics, University of Texas M.D. Anderson Cancer Center, Houston, Texas.
authors.forename: Brian P
authors.initials: BP
authors.lastname: Hobbs
authors.affiliation: Department of Nuclear Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas.
authors.forename: Nancy M
authors.initials: NM
authors.lastname: Swanston
authors.affiliation: Department of Nuclear Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas.
authors.forename: Michael
authors.initials: M
authors.lastname: Everding
authors.affiliation: Department of Nuclear Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas.
authors.forename: Tracy
authors.initials: T
authors.lastname: Moody
authors.affiliation: Department of Nuclear Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas.
authors.forename: Homer A
authors.initials: HA
authors.lastname: Macapinlac
mesh_terms: D000368:Aged; D001859:Bone Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D005260:Female; D005462:Fluorine Radioisotopes; D006801:Humans; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011379:Prognosis; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012863:Skeleton; D015899:Tomography, Emission-Computed, Single-Photon; D047368:Tumor Burden; D051598:Whole Body Imaging
chemical_list: D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals
keywords: NaF PET/CT; bone metastases; fluoride PET/CT; prostate cancer; skeletal tumor burden