Fig. 3

A comparison of two radiotherapy techniques delivering 66 Gy in 33 fractions to a locally-advanced lung tumor. Panels a-c show axial, coronal, and sagittal views of a hybrid-intensity-modulated radiotherapy (IMRT) plan; panels d-f show the corresponding views of a volumetric modulated arc therapy (VMAT) plan for the same tumor. Panel g shows the dose-volume histogram of the hybrid IMRT plan (triangles) and VMAT plan (squares); the red and blue lines to the right represent the planning target volume (PTV) and internal target volume (ITV) respectively; the remaining pair of blue lines represent the lung volume (lung tissue outside the PTV). PTV and ITV coverage is comparable for both techniques (g). The VMAT plan has a more conformal 95 % isodose (green line) around the PTV (d-f compared with a-c), however the maximum dose in the PTV is higher (g). The amount of lung receiving ≤20 Gy is very similar with both techniques (g), but the VMAT plan has a lower mean lung dose (19.5 Gy vs 22 Gy with hybrid-IMRT) and the hybrid-IMRT plan has more contralateral lung sparing, as seen by the position of low-dose isodose lines (orange [1320 cGy] and light blue [660 cGy])