Ultrasound scanning can be a valuable aid in radiation treatment planning. It provides an easy and accurate method of obtaining body outlines and cross-sections of the treatment fields. In many cases, ultrasound scanning can delineate the borders of a soft tissue tumor which cannot easily be delineated by other methods. Thus, the changes during and following irradiation therapy can be followed. Certain limitations in the technique of obtaining cross-sections, that must be pointed out, are the presence of good acoustic interfaces at the tumor margin, the blocking effect of gas filled structures and bone, and the presence of skin incisions. However, in all cases an accurate body outline can be obtained. It should also be pointed out that pulsed diagnostic ultrasound is painless, innocuous to underlying tissues, and easily applied; thus, ultrasound procedures may be repeated as often as needed.