Effects of Tumor-Rib Distance and Dose-Dependent Rib Volume on Radiation-Induced Rib Fractures in Patients with Breast Cancer

Abstract

Background Radiation-induced rib fracture (RIRF) is one of the adverse effects of conventional radiotherapy on breast cancer. This study aimed to investigate the effects of tumor-rib distance and dose-dependent rib volume on RIRFs in patients with breast cancer. Methods We retrospectively included 510 women with breast cancer who underwent curative surgical resection with subsequent adjuvant radiotherapy and were followed up using bone scintigraphy. Adjuvant radiotherapy was administered to the whole breast at 50 Gy in 25 fractions for 5 weeks and to the tumor bed at 10–16 Gy in 5–8 fractions. The tumor-rib distance was measured using preoperative computed tomography (CT) images. Postoperative chest wall thickness and dose-dependent rib volumes, which are absolute rib volumes receiving >20 Gy (V20), 30 Gy (V30), 40 Gy (V40), 45 Gy (V45), and 50 Gy (V50), were measured from the stimulation CT images for radiation treatment planning. RIRFs were identified using follow-up bone scintigraphy images. We assessed the relationship of RIRF with tumor-rib distance, postoperative chest wall thickness, and dose-dependent rib volumes. Results The median follow-up duration was 58.8 months, and 92 patients (18.0%) experienced RIRF. Univariate analysis revealed that osteoporosis, surgery type, radiation field, tumor-rib distance, postoperative chest wall thickness, V20, V30, V40, V45, and V50 were risk factors for RIRF (p<0.05). Patients with high values of tumor-rib distance and postoperative chest wall thickness had significantly lower risks of RIRF than those with low values. Patients with high values of V20, V30, V40, V45, and V50 had significantly higher risks of RIRF than those with low values. In multivariate analysis, tumor-rib distance and all five dose-dependent rib volumes, as well as osteoporosis and radiation field, were independent risk factors for RIRF (p<0.05). Conclusions Tumor-rib distance and dose-dependent rib volume were independent risk factors for RIRF in patients with breast cancer. Restriction of the absolute rib volumes in the radiation field could be effective in reducing the risk of RIRF.