ABSTRACT: PURPOSE:Chest wall (CW) pain and rib fractures are frequently diagnosed after stereotactic body radiation therapy (SBRT) for malignant lung tumors. We hypothesize that multiple risk factors, including bone mineral density (BMD), are associated with CW toxicity, and that CW pain and rib fractures often evolve into chronic clinical problems. METHODS AND MATERIALS:A total of 118 lung tumors treated with SBRT in 100 patients with a minimum follow-up period of 2 years were retrospectively analyzed. The incidence, clinical course, and related demographic, clinical, and dosimetric factors of CW pain and rib fractures were analyzed. In addition, BMD was assessed, and the radiographic appearance of radiation-induced rib fractures and their healing process were characterized. RESULTS:The median follow-up was 49 months (range, 24-106 months). CW pain developed in 33 of 118 treatments (28%) after, on average, 12.5 months (range, 0-50 months), and was more common in women (P = .04). The mean duration of CW pain was 25 months (range, 2-63 months), and 36% of patients never had resolution of CW pain. A total of 34 of 118 treatments (29%) resulted in rib fractures at a mean time of 22 months (range, 3-46 months); rib fractures were more common in women, African Americans, upper/middle lobe tumors, and patients with lower BMD (P < .05). The mean duration of rib fractures was 25 months (range, 5-41 months), and only 16 rib fractures (47%) healed. Shorter CW planning target volume distance resulted in a higher risk for both rib fractures and CW pain (P = .01). Sixty-seven percent of fractures developed surrounding soft tissue fibrosis, and 62% (21 of 34 fractures) heterotopic ossification. Diabetes, body mass index, and steroid use were not associated with CW pain or rib fracture. CONCLUSIONS:Several factors were associated with a higher risk of SBRT-related CW toxicity. Optimal CW sparing (eg, volumetric modulated arc therapy, lower dose per fraction) should be considered in this patient group without compromising tumor control. SBRT-induced rib fractures commonly heal abnormally and result in potential chronic CW pain.
