Characterization of Chest Wall Toxicity After Stereotactic Body Radiation Therapy to the Liver

Abstract

Chest wall rib fractures are frequent complications after thoracic stereotactic body radiation therapy (SBRT). While well described for lung SBRT, limited data exists on the frequency and predictors for chest wall toxicity with SBRT to the liver for primary or metastatic lesions. We aimed to characterize the clinical, demographic and dosimetric factors of rib fractures.A chart review identified 283 patients (204 male and 79 female) who received liver SBRT from 2014-2019. Univariate logistic regression models were used to identify demographic, clinical, and dosimetric factors associated with the development of rib fractures post liver SBRT. All statistical tests were two-sided and the null hypothesis was rejected for P < 0.05.The median follow-up was 12.2 months (range: 3-78.8 months). With respect to primary site, 81% were primary liver tumors and 19% metastases. SBRT doses ranged from 60 Gy in 5 fractions to 30 Gy in 5 fractions. The most commonly used doses were: 40 Gy in 5 fractions (29%), 45 Gy in 5 fractions (23%), 50 Gy in 5 fractions (18%), 35 Gy in 5 fractions (9%), 48 Gy in 3 fractions (8%), and 30 Gy in 5 fractions (5%). Mean PTV volume was 141 cc (range: 3.7 - 1304 cc). A total of 22 patients (8%) experienced rib fractures. Of these patients, three (17.6%) and one (6%) underwent two and three liver SBRT courses, respectively. The earliest rib fracture was seen 3 months after SBRT and the latest time point at which any rib fracture developed was 27 months. Female gender (2.29; 95% CI: 0.98-5.20; P = 0.049), increasing BED3 Gy (1.01; 95% CI: 1.00-1.01; P = 0.016), and BED10 Gy (1.02; 95% CI: 1.01-1.04; P = 0.009) were associated with an increased probability of developing rib fractures. Increasing distance from the PTV to the chest wall was associated with a lower probability of developing rib fractures (OR: 0.69; 95% CI: 0.52-0.88; P = 0.007). Mean distance from PTV to chest wall was 2.2 cm (range: 0 - 9.5 cm). Furthermore, increasing D30cc to the chest wall (OR: 1.09; 95% CI: 1.05-1.15; P < 0.001), maximum chest wall dose (OR: 1.1; 95% CI: 1.06-1.15; P < 0.001), V40Gy (OR: 1.08; 95% CI: 1.04-1.14; P < 0.001), V30Gy (OR: 1.02; 95% CI: 1.02-1.03; P < 0.001), V20Gy (1.003; 95% CI: 1.000-1.006; P = 0.016), V10Gy (1.002; 95% CI: 1.000-1.004; P = 0.05) were associated with an increased probability of developing rib fractures. Undergoing more than one course of SBRT to the liver (P = 0.34), PTV volume (P = 0.55), mean chest wall dose (P = 0.94), left versus right side tumors (P = 0.69) and BMI > 30 (P = 0.36) were not associated with the development of rib fractures.Rib fractures after liver SBRT are a rare event and were observed in 8% of patients. Clinicians should continue to utilize well-established dose constraints and minimize radiation dose delivery to the chest wall.