title: Fluorodeoxyglucose positron emission tomography response and normal tissue regeneration after stereotactic body radiotherapy to liver metastases.
abstract: OBJECTIVE
  To characterize changes in standardized uptake value (SUV) in positron emission tomography (PET) scans and determine the pace of normal tissue regeneration after stereotactic body radiation therapy (SBRT) for solid tumor liver metastases.
  
  
  METHODS
  We reviewed records of patients with liver metastases treated with SBRT to ≥40 Gy in 3-5 fractions. Evaluable patients had pretreatment PET and ≥1 post-treatment PET. Each PET/CT scan was fused to the planning computed tomography (CT) scan. The maximum SUV (SUV(max)) for each lesion and the total liver volume were measured on each PET/CT scan. Maximum SUV levels before and after SBRT were recorded.
  
  
  RESULTS
  Twenty-seven patients with 35 treated liver lesions were studied. The median follow-up was 15.7 months (range, 1.5-38.4 mo), with 5 PET scans per patient (range, 2-14). Exponential decay curve fitting (r=0.97) showed that SUV(max) declined to a plateau of 3.1 for controlled lesions at 5 months after SBRT. The estimated SUV(max) decay half-time was 2.0 months. The SUV(max) in controlled lesions fluctuated up to 4.2 during follow-up and later declined; this level is close to 2 standard deviations above the mean normal liver SUV(max) (4.01). A failure cutoff of SUV(max) ≥6 is twice the calculated plateau SUV(max) of controlled lesions. Parenchymal liver volume decreased by 20% at 3-6 months and regenerated to a new baseline level approximately 10% below the pretreatment level at 12 months.
  
  
  CONCLUSIONS
  Maximum SUV decreases over the first months after SBRT to plateau at 3.1, similar to the median SUV(max) of normal livers. Transient moderate increases in SUV(max) may be observed after SBRT. We propose a cutoff SUV(max) ≥6, twice the baseline normal liver SUV(max), to score local failure by PET criteria. Post-SBRT values between 4 and 6 would be suspicious for local tumor persistence or recurrence. The volume of normal liver reached nadir 3-6 months after SBRT and regenerated within the next 6 months.
authors.affiliation: Department of Radiation Oncology, University of Colorado Denver, Aurora, Colorado, USA. Michelle.Stinauer@ucdenver.edu
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Stinauer
authors.forename: Quentin
authors.initials: Q
authors.lastname: Diot
authors.forename: David C
authors.initials: DC
authors.lastname: Westerly
authors.forename: Tracey E
authors.initials: TE
authors.lastname: Schefter
authors.forename: Brian D
authors.initials: BD
authors.lastname: Kavanagh
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008099:Liver / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000502:physiology / Q000528:radiation effects; D008113:Liver Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000556:secondary / Q000601:surgery*; D008115:Liver Regeneration / Q000502:physiology / Q000528:radiation effects; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods; D009929:Organ Size; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D016634:Radiosurgery; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18