Evaluation of a commercial three-dimensional electron pencil beam algorithm

Results from beta testing of a commercially available three-dimensional electron pencil beam algorithm (CMS FOCUS, Computerized Medical Systems, Inc. St. Louis, MO) are reported. Straight on beams were evaluated at normal and extended distances, and obliquely incident beams at angles up to 40 degrees. Shaped electron fields with small circular cutouts, and narrow elongated, centered and offcentered, rectangular field shapes were investigated. Slab inhomogeneities were studied for lung and bone equivalent material, and isodose distributions for small inhomogeneities of these materials were compared with film and TLD measurements. All tests reported here were performed with electrons 6, 12, and 20 MeV from a Cl-1800 accelerator.