EXPERIMENTAL-VERIFICATION OF A 3-DIMENSIONAL DOSE CALCULATION ALGORITHM USING A SPECIALLY DESIGNED HETEROGENEOUS PHANTOM

A solid heterogeneous phantom made up of 25- and 50-mm cubes of materi als with different electron densities was used to verify the accuracy of a three-dimensional (3-D) dose calculation algorithm. This algorith m uses 3-D information obtained from contiguous CT (computed tomograph y) slices, spaced 5 mm apart. Primary and scatter doses at a point are calculated by using information from ray-tracing CT voxels. The algor ithm was developed on a Stardent model 1500 Supergraphic workstation. Cubes of materials with different electron densities were stacked up t o simulate finite heterogeneities in three dimensions. This design all ows verification of the algorithm for surface contour corrections and finite heterogeneities in the treatment field. Thermoluminescent lithi um fluoride chips were placed in grooves milled on the cubes for dose measurement at various points. Different experiments were performed to investigate both the accuracy of the dose calculation algorithm and t he utility of the versatile test phantom.