Dose-Response Model for Chest Wall Tolerance of Stereotactic Body Radiation Therapy

Many recent studies have described rib fractures and chest wall pain following stereotactic body radiation therapy (SBRT). Although these toxicities generally are not life-threatening, the chest wall and ribs are considered dose-limiting tissues because of the potential effect on patients׳ quality of life. Few studies have reported dose-response models that can provide quantitative estimates of risk as a function of dose and volume. Notably, Memorial Sloan Kettering Cancer Center (Mutter et al8) analyzed grade 2 or higher chest wall toxicity in a cohort of 126 patients treated with linear accelerator–based SBRT; the authors provided detailed dose-volume histogram (DVH) data to allow for pooled analyses. We pooled these 126 patients with an additional 44 patients treated with CyberKnife at the Erlanger Medical Center to create an updated dose-response model for chest wall tolerance. In the aggregate analysis, the 10% risk level for grade 2 or higher complications for D70 cc was 16.2 Gy in 4 fractions, and the 50% risk level was D70 cc = 65.1 Gy in 4 fractions. For D2 cc, the 10% and 50% risk levels in 4 fractions were 43.0 Gy and 87.9 Gy, respectively. These dose-tolerance limits may help quantify chest wall toxicity risks. Further research continues to determine more accurate estimates of grade 3 risk levels.