Application of Contrast-enhanced Ultrasound in Monitoring Soft Tissue Sarcoma Response to Neoadjuvant Radiotherapy

This pilot study will evaluate the feasibility of applying CEUS as imaging guidance for planning RT and predicting RT response. The investigators will determine if US-CT/MRI fusion is feasible and if tumor vascularity and pressure from CEUS can be used to reflect/predict the RT response. The investigators will perform CEUS three times: before the first neoadjuvant RT fraction, halfway through RT, and between the completion of RT and surgery. The fusion will be performed using previously acquired CT/MRI or on-site cone-beam CT with Bmode US. Once the fusion is successful, CEUS will be performed and panoramic 2D images (mimicking 3D) will be collected for the whole tumor. If the fusion is not feasible or successful, the investigators will perform CEUS side by side with CT/MRI and collect images. The investigators will quantify tumoral vascularity comparing Bmode area/volume (total tumor) and contrast-enhanced area/volume (vascular region) at each time point. Subharmonic amplitudes in the tumor area/volume will be quantified to estimate tumoral pressure (known to be the same level as interstitial fluid pressure (IFP)). Quantified vascularity and pressure at each time point will be compared with the tumor size change at later study points as well as the histological outcome after the surgery.