This report on electron-beam treatment planning is based on experience with both the electrons in the 6-to 24-mev range from the Allis-Chalmers betatron and those in the 15-to 35-mev range from the Brown-Boveri betatron. It is based primarily on treatment-planning experience in the United States, particularly as applied at the Memorial Hospital in New York since 1955. The treatmentplanning method in use at Memorial Hospital provides a systematic method for determining the actual dose distributions in a patient, taking into consideration wedges, surface irregularities, and tissue heterogeneities. The term comprehensive in the title of this report implies such corrections. Because of the large volume of cases treated at Memorial, it has been necessary to develop a system that could be routinely applied, making use of approximations wherever possible. Where indicated, even greater individualization can be accomplished by using the variation of correction factors with depth rather than averages. Annually, approximately 500 cases receive comprehensive treatment planning for external radiation as well as the 150 to 200 cases that receive comprehensive implant dosimetry planning.Since the absorption of electrons is determined by quite different processes from those applicable to x-rays, this system was based on the specific characteristics of electron absorption.'" Corrections in this system are applied by representing an isodose distribution by several depth-dose distributions along rays emanating from a virtual ~o u r c e .~'~ Segments of unit density depth-dose distributions are translated sequentially along a ray by an amount dependent on location, extent, and electron density of the inhomogeneous region. To examine the influence of inhomogeneities, the distribution of dose produced in a pressed wood phantom in which various materials were inserted was measured by either film or small cavity ionization chamber methods. Recent measurements have also employed highimpact polystyrene, a fairly new tissue-equivalent material, which is opaque and very convenient, especially for film measurements. The data in the following figures were obtained with 6-to 20-mev electrons through the following field sizes 198
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