Figure 9. (a) Dose-volume histogram (DVH) for a dose distribution comprised of eight uniform regions, calculated with a voxel size of 4 mm x 4 mm x 4 mm. The region of interest is placed centrally (heavy line), or displaced 2 mm laterally and 2 mm posteriorly (feint line). (b) DVHs for spherical structures of 6 cm, 8 cm and 10 cm diameter, calculated using either a 4 mm x 4 mm x 4 mm grid spacing (heavy lines) or a 2 mm x 2 mm x 2 mm grid spacing (feint lines). (c) DVHs for spherical structures of 6 cm, 8 cm and 10 cm diameter, calculated using Pinnacle³ (heavy lines) and an independent program (feint lines). Grid size is 4 mm x 4 mm x 5 mm.