Ultrasound-based localization.

Ultrasound is a noninvasive, relatively easy, rapid, and real-time imaging technique for organ targeting for radiotherapy. Its application has been developed to a greater extent in prostate cancer than in other sites in which it has been shown to improve the accuracy of daily treatment delivery. With the move toward dose escalation and the need to maximally spare the adjacent critical structures through more conformal therapy and smaller field margins, an innovative technique for accurate and reproducible tumor targeting is mandatory. Basic ultrasound principles and organ location lend themselves well to the application of this modality in prostate cancer. Promising results using daily ultrasound-guided B-mode acquisition and targeting for patients with upper abdominal tumors suggest an area for additional trials and study. For breast cancer radiotherapy, ultrasound serves to define involved primary and nodal sites, especially in patients in whom surgical evaluation will not be the first therapeutic step.