title: Modeling local control after hypofractionated stereotactic body radiation therapy for stage I non-small cell lung cancer: a report from the elekta collaborative lung research group.
abstract: OBJECTIVE
  Hypofractionated stereotactic body radiation therapy (SBRT) has emerged as an effective treatment option for early-stage non-small cell lung cancer (NSCLC). Using data collected by the Elekta Lung Research Group, we generated a tumor control probability (TCP) model that predicts 2-year local control after SBRT as a function of biologically effective dose (BED) and tumor size.
  
  
  METHODS
  We formulated our TCP model as follows: TCP = e([BED10 - c ∗ L - TCD50]/k) ÷ (1 + e([BED10 - c ∗ L - TCD50]/k)), where BED10 is the biologically effective SBRT dose, c is a constant, L is the maximal tumor diameter, and TCD50 and k are parameters that define the shape of the TCP curve. Least-squares optimization with a bootstrap resampling approach was used to identify the values of c, TCD50, and k that provided the best fit with observed actuarial 2-year local control rates.
  
  
  RESULTS
  Data from 504 NSCLC tumors treated with a variety of SBRT schedules were available. The mean follow-up time was 18.4 months, and 26 local recurrences were observed. The optimal values for c, TCD50, and k were 10 Gy/cm, 0 Gy, and 31 Gy, respectively. Thus, size-adjusted BED (sBED) may be defined as BED minus 10 times the tumor diameter (in centimeters). Our TCP model indicates that sBED values of 44 Gy, 69 Gy, and 93 Gy provide 80%, 90%, and 95% chances of tumor control at 2 years, respectively. When patients were grouped by sBED, the model accurately characterized the relationship between sBED and actuarial 2-year local control (r=0.847, P=.008).
  
  
  CONCLUSIONS
  We have developed a TCP model that predicts 2-year local control rate after hypofractionated SBRT for early-stage NSCLC as a function of biologically effective dose and tumor diameter. Further testing of this model with additional datasets is warranted.
authors.affiliation: Department of Radiation Oncology, Jefferson Medical College of Thomas Jefferson University, 111 S 11th St, Bodine Center, Rm G-301, Philadelphia, PA 19107, USA. ohri.nitin@gmail.com
authors.forename: Nitin
authors.initials: N
authors.lastname: Ohri
authors.forename: Maria
authors.initials: M
authors.lastname: Werner-Wasik
authors.forename: Inga S
authors.initials: IS
authors.lastname: Grills
authors.forename: José
authors.initials: J
authors.lastname: Belderbos
authors.forename: Andrew
authors.initials: A
authors.lastname: Hope
authors.forename: Di
authors.initials: D
authors.lastname: Yan
authors.forename: Larry L
authors.initials: LL
authors.lastname: Kestin
authors.forename: Matthias
authors.initials: M
authors.lastname: Guckenberger
authors.forename: Jan-Jakob
authors.initials: JJ
authors.lastname: Sonke
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bissonnette
authors.forename: Ying
authors.initials: Y
authors.lastname: Xiao
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology* / Q000601:surgery*; D016208:Databases, Factual; D019583:Dose Fractionation, Radiation; D006801:Humans; D053208:Kaplan-Meier Estimate; D008175:Lung Neoplasms / Q000473:pathology* / Q000601:surgery*; D015233:Models, Statistical; D016634:Radiosurgery / Q000379:methods*; D012062:Relative Biological Effectiveness; D047368:Tumor Burden / Q000528:radiation effects*