title: A cortical thickness and radiation dose mapping approach identifies early thinning of ribs after stereotactic body radiation therapy.
abstract: High rates of spontaneous rib fractures are associated with thoracic stereotactic body radiation therapy (SBRT). These fractures likely originate within the cortical bone and relate to the cortical thickness (Ct.Th). We report the development and application of a novel Ct.Th and radiation dose mapping technique to assess early site-specific changes of cortical bone in ribs.
  
  
  
  Rib Ct.Th maps were constructed from pre-SBRT and 3month post-SBRT CT scans for 28 patients treated for peripheral lung lesions. The Ct.Th at approximately 50,000 homologous points within the entire rib cage was determined pre- and post-SBRT. Each rib was then divided into 30 homologous regions. The mean dose and thinning were determined per section.
  
  
  
  Regions of ribs that received ⩾10Gy exhibited significant thinning of cortical bone (p=0.001). The mean Ct.Th percent difference (95% CI) in regions receiving 10-20Gy, 20-30Gy, 30-40Gy, and ⩾40Gy were -7% (-4%,-11%), -14% (-18%,-11%), -15% (-19%,-11%), and -18% (-22%,-15%) respectively. Regions receiving >20Gy experienced significantly more thinning than regions receiving lower doses.
  
  
  
  Substantial early cortical bone thinning was observed post-SBRT in regions of ribs that received ⩾10Gy. The rapid thinning of ribs may predispose ribs to fracture after SBRT.
authors.affiliation: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, USA; Department of Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Okoukoni
authors.affiliation: Department of Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, USA; Virginia Tech-Wake Forest University Center for Injury Biomechanics, Winston-Salem, USA.
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Lynch
authors.affiliation: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, USA.
authors.forename: Emory R
authors.initials: ER
authors.lastname: McTyre
authors.affiliation: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Randolph
authors.affiliation: Department of Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, USA; Virginia Tech-Wake Forest University Center for Injury Biomechanics, Winston-Salem, USA.
authors.forename: Ashley A
authors.initials: AA
authors.lastname: Weaver
authors.affiliation: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, USA.
authors.forename: A William
authors.initials: AW
authors.lastname: Blackstock
authors.affiliation: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, USA.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Lally
authors.affiliation: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, USA; Department of Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, USA.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Munley
authors.affiliation: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, USA. Electronic address: jwilley@wakehealth.edu.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Willey
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D008875:Middle Aged; D011832:Radiation Injuries / Q000209:etiology; D016634:Radiosurgery / Q000009:adverse effects* / Q000379:methods; D011879:Radiotherapy Dosage; D012253:Rib Fractures / Q000209:etiology; D012272:Ribs / Q000473:pathology / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed
keywords: Bone; Diagnostic imaging; Lung cancer; Rib fracture; Stereotactic body radiation therapy (SBRT); Stereotactic radiation surgery (SRS)