title: Incidence, risk factors, and dose-volume relationship of radiation-induced rib fracture after carbon ion radiotherapy for lung cancer.
abstract: BACKGROUND
  The purpose of this study was to assess the incidence, risk factors, and dose-volume relationship of radiation-induced rib fracture (RIRF) after carbon ion radiotherapy for lung cancer.
  
  
  METHODS
  Fifty-seven ribs of 18 patients with peripheral stage I non-small cell lung cancer treated with carbon ion radiotherapy were analyzed on rib fracture. The patients were treated at a total dose of 52.8 Gy [relative biologic effectiveness (RBE)] or 60.0 Gy (RBE) in 4 fractions and were followed at least six months. Patient characteristics and dosimetric parameters were analyzed for associations with RIRF.
  
  
  RESULTS
  Eighteen patients and 57 ribs were included in this study. The median length of follow-up was 36.5 months. RIRF was observed in seven (39%) of the 18 patients, and in 11 (19%) of 57 ribs. Only one patient developed symptomatic fracture. The distance from the ribs to the tumor site was significantly shorter in fractured ribs than in non-fractured ribs (1.4 ± 0.3 cm vs. 2.5 ± 0.3 cm). Receiver operating characteristic curve analysis showed that [Formula: see text] as a cut-off value for discriminating RIRF had the largest area under the curve (AUC =0.78). Comparison of the two-year cumulative incidence of RIRF among two groups as determined by cut-off values, yielded the following result: 53% vs. 4% [[Formula: see text], ≥ 38.2 Gy (RBE) or less]. Results from the two groups were significantly different (p < 0.05).
  
  
  CONCLUSIONS
  The crude incidence of RIRF after carbon ion radiotherapy was 39% but incidence of symptomatic fracture was low. The [Formula: see text] as cut-off values may be helpful for discriminating the risk of RIRF.
authors.affiliation: a Gunma University , Department of Radiation Oncology , Maebashi , Japan .
authors.forename: Takanori
authors.initials: T
authors.lastname: Abe
authors.affiliation: a Gunma University , Department of Radiation Oncology , Maebashi , Japan .
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Shirai
authors.affiliation: a Gunma University , Department of Radiation Oncology , Maebashi , Japan .
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Saitoh
authors.affiliation: c Gunma Prefectural Cancer center , Ohta , Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ebara
authors.affiliation: b Gunma University Heavy Ion Medical Center , Maebashi , Japan , and.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Shimada
authors.affiliation: b Gunma University Heavy Ion Medical Center , Maebashi , Japan , and.
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Tashiro
authors.affiliation: a Gunma University , Department of Radiation Oncology , Maebashi , Japan .
authors.forename: Naoko
authors.initials: N
authors.lastname: Okano
authors.affiliation: b Gunma University Heavy Ion Medical Center , Maebashi , Japan , and.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ohno
authors.affiliation: a Gunma University , Department of Radiation Oncology , Maebashi , Japan .
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakano
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D063193:Heavy Ion Radiotherapy / Q000009:adverse effects*; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D011832:Radiation Injuries / Q000453:epidemiology / Q000209:etiology*; D011879:Radiotherapy Dosage; D012062:Relative Biological Effectiveness; D012253:Rib Fractures / Q000453:epidemiology* / Q000209:etiology*; D012307:Risk Factors