Dosimetric predictors of chest wall pain after lung stereotactic body radiotherapy

Purpose: To identify risk factors for the development of chest wall (CW) pain after thoracic stereotactic body radiotherapy (SBRT). Methods and materials: A registry of patients with lung lesions treated with lung SBRT was explored to identify patients treated with 54 Gy in three fractions or 50 Gy in five fractions. One hundred and forty-six lesions in 140 patients were identified; complete electronic treatment plans were available on 86 CWs. The CW was contoured as a 3 cm outward expansion from the involved lung. Univariate and multivariate analyses were used to correlate patient, tumor, and dosimetric factors to the development of CW toxicity. Results: CW pain occurred in 22 patients (15.7%). The Kaplan–Meier estimated risk of CW pain at 2 years was 20.1% (95% C.I., 13.2–28.8%). On univariate analysis of patient factors, elevated BMI (p = 0.026) and connective tissue disease (p = 0.036) correlated with CW pain. The percent of CW receiving 30, 35, or 40 Gy was most predictive of CW pain on multivariate analysis using logistic regression, while V40 alone was predictive using Cox regression. A V30 threshold of 0.7% and V40 threshold of 0.19% was correlated with a 15% risk of CW pain. Conclusions: We have described patient and dosimetric parameters that correlate with CW pain after lung SBRT. The risk of CW pain may be mitigated by attempting to reduce the relative proportion of CW receiving 30–40 Gy during treatment planning.