Would you consider SBRT for a retroperitoneal sarcoma with an R2 resection near critical structures precluding re-resection?  

This is a great question. The area of risk in R2 resections are the residual disease and the entire retroperitoneum. Thus, if feasible, the post-op retroperitoneal volume should be treated to 66 Gy (due to the R2 resection) as it is at high risk for recurrence. One could consider boosting the residu...