Recent trends toward higher doses and larger volumes in the treatment of lymphomas require careful shielding of adjacent normal tissues. The purpose of this discussion is to present the method used in the Radiation Therapy Department of the Presbyterian-St. Luke's Hospital, Chicago, for building lead shielding tailored to the individual patient. This method is accurate, uses inexpensive materials and tools, and is relatively simple. Protection of vital, normal structures in patients undergoing extended field therapy was provided by a variety of standard lead blocks of various sizes and shapes. None of these gave optimal or even very satisfactory protection. It quickly became apparent that shielding custom-tailored to the individual patient would be necessary to provide satisfactory shielding of normal structures. Templates for the lead shields are produced by the following method: With the patient and the shield-supporting satellite placed at identical distances from the focal spot as they will be from the source during therapy, a simulator film is taken with a film beneath the patient and a 1/2-inch chicken-wire grid placed immediately above the satellite (Fig. 1, A). This produces a roentgenogram of the patient with a magnified image of the grid superimposed (Fig. 2, A). A second roentgenogram is made with the film placed on the satellite immediately under the same chicken-wire grid (Fig. 1, B). This produces a filn showing only an unmagnified grid (Fig. 2, B). The area to be protected is then outlined by the radiotherapist on the simulator film of the patien with the superimposed magnified grid (Fig. 3, A) This outline is then reproduced on the plain filn with the unmagnified grid, using it as a reference (Fig. 3, B). This outline, reduced in size, represents the true size of the lead shields and can be used directly as the template for building the lead blocks. Initially, this template was used to cut the lead shield out of a solid lead block either by band-sawing, jigsawing, or milling. The extremely poor cutting qualities of lead, even when hardened by small percentages of various other metals, makes this method frustratingly slow and sometimes even dangerous. We have long since switched to our current method which employs the low melting point of lead. The template is taped to a 2-inch thick Styrofoam sheet, and an outline is cut out on a fine jigsaw. We have used the Dremel hobby jigsaw which has an adequate capacity for this purpose and makes a cut sufficiently fine to turn essentially right-angled corners. Styrofoam is used in making the patterns because it is easily dug out of the mold; a wood pattern might work well, but great care would be necessary in removing it from the plaster to avoid fracturing the mold. Two-inch-thick patterns, Styrofoam or otherwise, will yield lead blocks something slightly less than 2 inches thick which represent something over 4 mm h.v.l. shielding for cobalt-60 teletherapy.
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Fordham et al. (1969) studied this question.