Benchmarking of three-dimensional RTP dose distributions in heterogeneous phantoms using BEAM

To examine the accuracy of dose calculation algorithms in heterogeneous phantoms, comparisons with measurements are usually performed. However, measurements were generally limited to central axis due to the difficulty and complexity of performing accurate 3D measurements using existing dosimetry tools and equipments. Therefore, there is a need for a detailed study and examination of 3D RTP (radiotherapy treatment planning) dose distributions in heterogeneous phantoms since more clinics start using inhomogeneity corrections in planning. In this work, we compare the dose distributions from the FOCUS RTP system in heterogeneous phantoms with those from the BEAM Monte Carlo code system. The phantom inhomogeneities mimic relevant clinical treatment sites, which include lung slab, lung-bone slab, bone-lung slab, mediastinum and tumor geometries. The benchmark comparisons were performed in lung densities of 0.20 and 0.31 g/cm/sup 3/, and a bone density of 2.40 g/cm/sup 3/ for 5/spl times/5 cm and 10/spl times/10 cm, 6 and 15 MV Varian Clinac photon beams. The measurement-based Clarkson and model-based multigrid superposition algorithms are examined.