B-scan ultrasound can be a useful adjunct in the accurate placement of radiation therapy treatment ports in selected cases. In addition to providing information of value in the determination of field size and shape, the display of a lesion’s contour in cross section can be of use in the selection of multiple ports for optimal distribution of radiation. In addition, the rate of regression of a neoplasm during and after therapy may be documented. The technique, however, is limited by the horizontal resolution of the transducer, the presence of good acoustic interfaces at the tumor margin, and the blocking effect of gas within superimposed hollow viscera. Therefore, in many instances little useful information is obtained. However, because pulsed diagnostic ultrasound is innocuous,6 painless, and easily applied, its continued application and development is justified.