An "all-shape" diaphragm for high-energy teletherapy units.

Abstract

In conventional deep x-ray therapy the useful beam area to the skin is attained by cones or adjustable rectangular diaphragms modified, when desired, by strips or “cut-outs” of lead or lead rubber. With cobalt-60 therapy, because of the high energy of the gamma rays, such a modification does not offer sufficient skin protection, and, as a result, the portals are generally limited to square or rectangular shapes. Since it is desirable that therapy fields conform to the presenting pathological pattern, we have designed a simple, adjustable diaphragm which gives essentially any field shape. The variation in field shape is obtained by the manual adjustment of a number of lead plates, each 2×6×3/8 inch thick. This adjustment can be made in less than a minute. Table Construction The lead plates and their supporting table are not connected in any way with the teletherapy unit but are positioned between it and the patient. The supporting table is constructed of 2×1/4-inch angle iron, and measures 44 inches long b...