The role of a radiation therapy (RT) boost for positive margins following pre-operative RT and surgery in extremity soft tissue sarcomas (STS) is unclear. We assessed the contribution of a boost to local control (LC), disease-free survival (DFS), and overall survival (OS).

We identified 67 patients treated from 1987 to 2011 with pre-operative RT and surgery with positive margin(s). Select patients received a boost delivered as peri-operative Iridium-192 brachytherapy (BRT), intra-operative electrons (IORT), or post-operative external beam RT (EBRT).

Ten patients received no RT boost, 10 received a BRT or IORT boost, and 47 received an EBRT boost. Five-year LC rates for no boost, BRT/IORT boost, and EBRT boost were 100%, 78%, and 71% (P = 0.5). On multivariate analysis, there were no significant predictors for LC. Variables associated with improved DFS rates were single positive margin (P = 0.007) and low tumor grade (P = 0.03). Tumor size <5 cm (P = 0.003), low grade (P = 0.001), and boost (P = 0.02) were associated with longer survival.

We did not identify a LC advantage for an RT boost. Given the unidentified selection factors for delivery of boost and its potential toxicities, its role in this setting remains unproven.