Lung Cancer 79 (2013) 161–166 Contents lists available at SciVerse ScienceDirect Lung Cancer j our na l ho me p age: www.elsevier.com/locate/lungcan Clinical prognostic factors and grading system for rib fracture following stereotactic body radiation therapy (SBRT) in patients with peripheral lung tumors Su Ssan Kim a , Si Yeol Song a , Jungwon Kwak a , Seung Do Ahn a , Jong Hoon Kim a , Jung Shin Lee b , Woo Sung Kim b , Sang-We Kim b , Eun Kyung Choi a,∗ a Department of Radiation Oncology, Asan Medical Center, University of Ulsan, College of Medicine, Seoul, Republic of Korea b Department of Internal Medicine, Asan Medical Center, University of Ulsan, College of Medicine, Seoul, Republic of Korea a r t i c l e i n f o Article history: Received 7 June 2012 Received in revised form 17 September 2012 Accepted 24 October 2012 Keywords: Lung tumor Stereotactic body radiation therapy Rib fracture Risk factors a b s t r a c t Background: Several studies reported rib fractures following stereotactic body radiation therapy (SBRT) for peripheral lung tumors. We tried to investigate risk factors and grading system for rib fractures after SBRT. Methods: Of 375 primary or metastatic lung tumors (296 patients) which were treated with SBRT at the Asan Medical Center (2006–2009), 126 lesions (118 patients) were adjacent to the chest-wall (<1 cm) and followed-up with chest computed tomography (CT) for >6 months; these were investigated in the present retrospective study. Three to four fractional doses of 10–20 Gy were delivered to 85–90% iso-dose volume of the isocenter dose. Rib fracture grade was defined from follow-up CT scans as the appearance of a fracture line (Gr1), dislocation of the fractured rib by more than half the rib diameter (Gr2), or the appearance of adjacent soft tissue edema (Gr3). Chest wall pain was assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) v3.0. Correlations between dose–volume data and the development of rib fracture were then analyzed. The Kaplan–Meier method, log-rank tests, and chi-square tests were used for statistical analysis. Results: The median age of the patients was 69 years (range: 19–90). Over a median follow-up period of 22 months (range: 7–62), 48 cases of rib fracture were confirmed. Median time to rib fracture was 17 months (range: 4–52). The 2-year actuarial risk of rib fracture was 42.4%. Maximal grade was Gr1 (n = 28), Gr2 (n = 8), or Gr3 (n = 15). The incidence of moderate to severe chest wall pain (CTCAE Gr ≥ 2) increased with maximal fracture grade (17.5% for Gr0–1 and 60.9% for Gr2–3; p < 0.001). Multivariate analysis identified female gender, lateral location, and the dose to the 8cc of the chest wall as significant prognostic factors. Conclusions: Female gender and lateral tumor location were clinical risk factors for rib fracture in the present study. Efforts to decrease chest wall dose should be made to reduce the risk of the rib fracture, particularly in high-risk patients. © 2012 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Stereotactic body radiation therapy (SBRT) provides local con- trol rates of approximately 90% in patients with early-stage, inoperable non-small-cell lung cancer (NSCLC) [1–4]. Furthermore, research suggests that SBRT results in comparable local control rates to surgery in patients with potentially operable stage I NSCLC [5]. The introduction of SBRT may thus lead to a decrease in the ∗ Corresponding author at: 388-1 Pungnap2-dong, Songpa-gu, Seoul 138-736, Republic of Korea. Tel.: +82 2 3010 4427; fax: +82 2 486 7258. E-mail address: ekchoi@amc.seoul.kr (E.K. Choi). proportion of untreated elderly NSCLC patients and improve sur- vival rates [6]. In general, the severity and incidence of acute and late toxic- ity following SBRT is low, even in elderly patients [7]. However, several authors have reported the development of rib fracture, and have performed analyses to identify dosimetric risk factors [8–13]. However, these studies have reported inconsistent results due to differences in patient selection and fractionation schemes. Furthermore, no previous study has thoroughly investigated the relationship between rib fracture and clinical parameters with an influence on dose–response. In addition, to the best of our knowledge, no grading system for the severity of rib fracture following SBRT has yet been pro- posed. A previous report used the Common Terminology Criteria 0169-5002/$ – see front matter © 2012 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lungcan.2012.10.011