title: Dose-effect analysis of radiation induced rib fractures after thoracic SBRT.
abstract: To determine a dose-effect relation for radiation induced rib fractures after stereotactic body radiation therapy (SBRT) in early stage non-small cell lung cancer (NSCLC). Automatic rib delineation has enabled the analysis of a large patient group.
  
  
  
  Four-hundred and sixty-six patients with stage I/II NSCLC received SBRT with a median of 54Gy in 3 fractions. The optimal EQD2-corrected dose parameter to predict (a)symptomatic fractures was found using Cox regression. Three normal tissue complication probability (NTCP) models based on this optimal parameter were constructed: (1) at a median follow up (FU) of 26months, (2) for all data, with time to toxicity taken into account and (3) at a FU of 26months, excluding low dose ribs.
  
  
  
  The median time to fracture was 22 (range 5-51) months. Maximum rib dose best predicted fractures. The TD50(dose with 50% complication) of the second NTCP model was 375Gy. The TD50was significantly higher for the other models indicating an under-estimation of the dose effect at the median follow-up time and/or when excluding low dose ribs.
  
  
  
  The risk of symptomatic rib fractures after SBRT was significantly correlated to dose, and was <5% at 26months when Dmax<225Gy.
authors.affiliation: Department of Radiation Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Barbara
authors.initials: B
authors.lastname: Stam
authors.affiliation: Department of Radiation Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Erik
authors.initials: E
authors.lastname: van der Bijl
authors.affiliation: Department of Radiation Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Heike
authors.initials: H
authors.lastname: Peulen
authors.affiliation: Department of Radiation Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Maddalena M G
authors.initials: MMG
authors.lastname: Rossi
authors.affiliation: Department of Radiation Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: José S A
authors.initials: JSA
authors.lastname: Belderbos
authors.affiliation: Department of Radiation Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands. Electronic address: j.sonke@nki.nl.
authors.forename: Jan-Jakob
authors.initials: JJ
authors.lastname: Sonke
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D011832:Radiation Injuries / Q000209:etiology*; D016634:Radiosurgery / Q000009:adverse effects*; D012253:Rib Fractures / Q000209:etiology*
keywords: Dose–effect; Lung cancer; NTCP; Rib fracture; SBRT