Rib fracture after stereotactic radiotherapy for primary lung cancer: prevalence, degree of clinical symptoms, and risk factors

Atsushi Nambu,Tsutomu Araki,Tsuyota Koshiishi,Ryoh Saito,Takafumi Komiyama,Shinichi Aoki,Yoshiyasu Maehata,Eiichi Sawada,Masayuki Araya,Hiroshi Onishi,Licht Tominaga,Kengo Kuriyama,Kan Marino

doi:10.1186/1471-2407-13-68

Abstract

BackgroundAs stereotactic body radiotherapy (SBRT) is a highly dose-dense radiotherapy, adverse events of neighboring normal tissues are a major concern. This study thus aimed to clarify the frequency and degree of clinical symptoms in patients with rib fractures after SBRT for primary lung cancer and to reveal risk factors for rib fracture. Appropriate α/β ratios for discriminating between fracture and non-fracture groups were also investigated.MethodsBetween November 2001 and April 2009, 177 patients who had undergone SBRT were evaluated for clinical symptoms and underwent follow-up thin-section computed tomography (CT). The time of rib fracture appearance was also assessed. Cox proportional hazard modeling was performed to identify risk factors for rib fracture, using independent variables of age, sex, maximum tumor diameter, radiotherapeutic method and tumor-chest wall distance. Dosimetric details were analyzed for 26 patients with and 22 randomly-sampled patients without rib fracture. Biologically effective dose (BED) was calculated with a range of α/β ratios (1–10 Gy). Receiver operating characteristics analysis was used to define the most appropriate α/β ratio.ResultsRib fracture was found on follow-up thin-section CT in 41 patients. The frequency of chest wall pain in patients with rib fracture was 34.1% (14/41), and was classified as Grade 1 or 2. Significant risk factors for rib fracture were smaller tumor-chest wall distance and female sex. Area under the curve was maximal for BED at an α/β ratio of 8 Gy.ConclusionsRib fracture is frequently seen on CT after SBRT for lung cancer. Small tumor-chest wall distance and female sex are risk factors for rib fracture. However, clinical symptoms are infrequent and generally mild. When using BED analysis, an α/β ratio of 8 Gy appears most effective for discriminating between fracture and non-fracture patients.

Highlights

As stereotactic body radiotherapy (SBRT) is a highly dose-dense radiotherapy, adverse events of neighboring normal tissues are a major concern
Several studies have reported complications related to SBRT for lung cancer, including radiation pneumonitis [7] and chest wall injuries such as rib fracture [8,9,10]
We evaluated the correlation between the timing of rib fracture appearance and Biologically effective dose (BED) at the α/β ratio defined above in the 26 patients with rib fracture using Pearson’s correlation coefficient

Summary

Introduction

As stereotactic body radiotherapy (SBRT) is a highly dose-dense radiotherapy, adverse events of neighboring normal tissues are a major concern. This study aimed to clarify the frequency and degree of clinical symptoms in patients with rib fractures after SBRT for primary lung cancer and to reveal risk factors for rib fracture. Stereotactic body radiotherapy (SBRT) has emerged as a new treatment for stage I lung cancer. Several studies have reported complications related to SBRT for lung cancer, including radiation pneumonitis [7] and chest wall injuries such as rib fracture [8,9,10]. The reported frequencies of rib fracture after SBRT are generally higher than those associated with other methods of radiotherapy, such as tangential breast irradiation in breast-conserving therapy. If an adverse event often proves asymptomatic, clinicians should not overemphasize the risks

Objectives

Methods

Results

Discussion

Conclusion