title: Microscopic and macroscopic tumor and parenchymal effects of liver stereotactic body radiotherapy.
abstract: OBJECTIVE
  To describe the histologic and volumetric changes in normal liver tissue after stereotactic body radiotherapy (SBRT) for liver metastases.
  
  
  METHODS
  Pre- and post-SBRT imaging studies were analyzed to evaluate the effect of SBRT on normal liver volume (NLV) in 15 patients treated in a prospective clinical trial. Two other patients underwent exploratory surgery after SBRT and histologic analyses of the irradiated liver were performed to characterize the pathologic effects of SBRT.
  
  
  RESULTS
  In the 15 patients studied quantitatively, the total NLV had decreased transiently at 2-3 months after SBRT and then began to regenerate at 3-8 months after SBRT. The median NLV reduction at the maximal observed effect was 315 cm(3) (range, 125-600) or 19% (range, 13-33%). Among the several dosimetric parameters evaluated, the strongest linear correlation was noted for the NLV percentage receiving 30 Gy as a predictor of maximal NLV reduction (r(2) = 0.72). The histologic changes observed 2 and 8 months after SBRT demonstrated distinct zones of tissue injury consistent with localized veno-occlusive disease.
  
  
  CONCLUSIONS
  The well-demarcated focal parenchymal changes after liver SBRT (demonstrated both radiographically and histologically) within the high-dose zone are consistent with a threshold dose-induced set of phenomena. In contrast, the more global effect of NLV reduction, which is roughly proportional to whole organ dose parameters, resembles more closely an effect determined from radiobiologically parallel architecture. These observations suggest that modeling of normal tissue effects after liver SBRT might require different governing equations for different classes of effects.
authors.affiliation: Department of Radiation Oncology, University of Colorado, Denver, Aurora, CO 80045-000508, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Olsen
authors.forename: J
authors.initials: J
authors.lastname: Welsh
authors.forename: B D
authors.initials: BD
authors.lastname: Kavanagh
authors.forename: W
authors.initials: W
authors.lastname: Franklin
authors.forename: M
authors.initials: M
authors.lastname: McCarter
authors.forename: H R
authors.initials: HR
authors.lastname: Cardenes
authors.forename: L E
authors.initials: LE
authors.lastname: Gaspar
authors.forename: T E
authors.initials: TE
authors.lastname: Schefter
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004307:Dose-Response Relationship, Radiation; D004938:Esophageal Neoplasms / Q000473:pathology; D006504:Hepatic Veno-Occlusive Disease / Q000209:etiology / Q000473:pathology; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging / Q000473:pathology / Q000528:radiation effects*; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000556:secondary / Q000601:surgery*; D008115:Liver Regeneration; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D011832:Radiation Injuries / Q000473:pathology*; D016634:Radiosurgery; D012004:Rectal Neoplasms / Q000473:pathology; D047368:Tumor Burden