title: Lung volume reduction after stereotactic ablative radiation therapy of lung tumors: potential application to emphysema.
abstract: OBJECTIVE
  Lung volume reduction surgery (LVRS) improves dyspnea and other outcomes in selected patients with severe emphysema, but many have excessive surgical risk for LVRS. We analyzed the dose-volume relationship for lobar volume reduction after stereotactic ablative radiation therapy (SABR) of lung tumors, hypothesizing that SABR could achieve therapeutic volume reduction if applied in emphysema.
  
  
  METHODS
  We retrospectively identified patients treated from 2007 to 2011 who had SABR for 1 lung tumor, pre-SABR pulmonary function testing, and ≥6 months computed tomographic (CT) imaging follow-up. We contoured the treated lobe and untreated adjacent lobe(s) on CT before and after SABR and calculated their volume changes relative to the contoured total (bilateral) lung volume (TLV). We correlated lobar volume reduction with the volume receiving high biologically effective doses (BED, α/β = 3).
  
  
  RESULTS
  27 patients met the inclusion criteria, with a median CT follow-up time of 14 months. There was no grade ≥3 toxicity. The median volume reduction of the treated lobe was 4.4% of TLV (range, -0.4%-10.8%); the median expansion of the untreated adjacent lobe was 2.6% of TLV (range, -3.9%-11.6%). The volume reduction of the treated lobe was positively correlated with the volume receiving BED ≥60 Gy (r(2)=0.45, P=.0001). This persisted in subgroups determined by high versus low pre-SABR forced expiratory volume in 1 second, treated lobe CT emphysema score, number of fractions, follow-up CT time, central versus peripheral location, and upper versus lower lobe location, with no significant differences in effect size between subgroups. Volume expansion of the untreated adjacent lobe(s) was positively correlated with volume reduction of the treated lobe (r(2)=0.47, P<.0001).
  
  
  CONCLUSIONS
  We identified a dose-volume response for treated lobe volume reduction and adjacent lobe compensatory expansion after lung tumor SABR, consistent across multiple clinical parameters. These data serve to inform our ongoing prospective trial of stereotactic ablative volume reduction (SAVR) for severe emphysema in poor candidates for LVRS.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Binkley
authors.affiliation: Division of Thoracic Surgery, Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, California; Stanford Cancer Institute, Stanford University School of Medicine, Stanford, California.
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Shrager
authors.affiliation: Department of Radiology, Stanford University School of Medicine, Stanford, California.
authors.forename: Ann N
authors.initials: AN
authors.lastname: Leung
authors.affiliation: Department of Health Research & Policy, Stanford University School of Medicine, Stanford, California.
authors.forename: Rita
authors.initials: R
authors.lastname: Popat
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California; Department of Radiation Oncology, University of Southern California Keck School of Medicine, Los Angeles, California.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Trakul
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California.
authors.forename: Todd F
authors.initials: TF
authors.lastname: Atwood
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California.
authors.forename: Aadel
authors.initials: A
authors.lastname: Chaudhuri
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California; Stanford Cancer Institute, Stanford University School of Medicine, Stanford, California.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Maxim
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California; Stanford Cancer Institute, Stanford University School of Medicine, Stanford, California; Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, California. Electronic address: Diehn@Stanford.edu.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Diehn
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California; Stanford Cancer Institute, Stanford University School of Medicine, Stanford, California. Electronic address: BWLoo@Stanford.edu.
authors.forename: Billy W
authors.initials: BW
authors.lastname: Loo
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000601:surgery*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008175:Lung Neoplasms / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009929:Organ Size / Q000528:radiation effects*; D011013:Pneumonectomy / Q000379:methods; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D016634:Radiosurgery / Q000379:methods*; D012062:Relative Biological Effectiveness; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed