Incidence and Risk Factors for Chest Wall Toxicity After Risk-Adapted Stereotactic Radiotherapy for Early-Stage Lung Cancer

Introduction: High local control rates are reported after stereotactic ablative body radiotherapy (SABR) in stage I non-small cell lung cancer. Toxicity is uncommon, but few reports on long-term follow-up are available. We studied the incidence of chest wall pain (CWP) and rib fractures in patients with long-term follow-up. Methods: Between 2003 and 2009, 500 patients (530 tumors) underwent SABR using risk-adapted fractionation schemes, consisting of three fractions of 20 Gy, five fractions of 12 Gy, or eight fractions of 7.5 Gy. Toxicity data were collected in a prospective database and scored using Common Terminology Criteria for Adverse Events (CTCAE) version 4.03. Chest wall volumes receiving doses of 30, 40, 45, and 50 Gy (V30 Gy-V50 Gy) and maximum dose in 2 cm3 of chest wall (D2 ml) were determined for patients with CWP or rib fractures (n = 57). Results: With a median follow-up of 33 months, the 3-year overall survival and local control rates were 53.1% and 90.4%, respectively. CWP developed in 11.4% of patients and was severe (grade 3) in 2.0%. Rib fractures were observed in eight patients (1.6%), accompanied by CWP in seven of these patients. On multivariate analysis, patients with CWP had larger treatment volumes and shorter tumor-chest wall distances, whereas patients with rib fractures had larger tumor diameters and treatment volumes. Grade 3 CWP and rib fractures were associated with larger volumes of chest wall receiving doses of 30 to 50 Gy and rib fractures specifically with a higher maximum dose in the chest wall. Conclusions: Severe (grade 3) chest wall toxicity is uncommon after risk-adapted SABR and manifests in 2% or fewer of patients.