title: The significance of PTV dose coverage on cancer control outcomes in early stage non-small cell lung cancer patients treated with highly ablative stereotactic body radiation therapy.
abstract: OBJECTIVE
  We evaluated whether patients with early-stage non-small-cell lung cancers (NSCLCs) treated with stereotactic body radiation therapy (SBRT) without full prescription dose coverage of the planning target volume (PTV) had inferior outcomes.
  
  
  METHODS
  The SBRT regimen was 54 Gy in three fractions. Dosimetric constraints were as per the Radiation Therapy Oncology Group 0236 guidelines. All patients underwent four-dimensional CT (4D-CT) simulation. The internal target volume (ITV) was defined using 4D-CT, and the PTV was defined as a 6-mm longitudinal and a 3-mm axial expansion from the ITV. If normal tissue constraints were beyond tolerance, ITV-based dosing was employed where priority was made for full ITV coverage at the expense of PTV coverage. Patients with and without full PTV dose coverage were compared, and control rates were estimated using Kaplan-Meier analysis.
  
  
  RESULTS
  120 NSCLC cases were evaluated with 81% having adequate PTV dose coverage. ITV and PTV were significantly larger in the cohort with inadequate PTV dose coverage (p = 0.0085 and p = 0.0038, respectively), and the mean ITV and PTV doses were higher in patients with adequate PTV dose coverage (p = 0.002 and p < 0.0001, respectively). The 3-year local control rate was 100% for both cohorts. There was no difference in 3-year regional control (p = 0.36), disease-specific survival (p = 0.79) or overall survival (p = 0.73).
  
  
  CONCLUSIONS
  When delivering a highly ablative SBRT regimen for early-stage NSCLC, full-dose coverage of the ITV is sufficient for local control.
  
  
  CONCLUSIONS
  Our data are among the first to evaluate the utility of PTV margins in a highly ablative SBRT regimen and suggest that when dosing constraints cannot be met, full tumouricidal dose coverage of the ITV is sufficient for local control.
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Narek
authors.initials: N
authors.lastname: Shaverdian
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Tenn
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Darlene
authors.initials: D
authors.lastname: Veruttipong
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: John
authors.initials: J
authors.lastname: Hegde
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Chul
authors.initials: C
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Minsong
authors.initials: M
authors.lastname: Cao
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Nzhde
authors.initials: N
authors.lastname: Agazaryan
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Steinberg
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Kupelian
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Percy
authors.initials: P
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery*; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D053208:Kaplan-Meier Estimate; D008168:Lung / Q000000981:diagnostic imaging; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D016896:Treatment Outcome