Fig. 4

A case of T2N0 Nasopharyngeal carcinoma recurred 63 months after IMRT. The upper panel shows the axial, coronal and sagittal images of a RIR mapped rGTV on the original pCT where its centroid is located at CTV1and the 95 % rGTV volume contained on more peripheral PTV2 (contour not shown). The middle panel shows DIR mapped rGTV on the original pCT where its centroid located at GTV and the 95 % rGTV volume contained on more peripheral CTV2. The lower panel shows RIR and DIR mapped rGTVs overlaid to plan isodose line. Note that RIR rGTV fD95% extends beyond the 95 % isodose line “66.5 Gy” (red arrow in sagittal image) which would erroneously characterize it as type B failure, while in fact DIR shows it as a type A failure (i.e. the fD95% of DIR mapped rGTV is completely encapsulated with 95 % isodose line, shown by white arrow in sagittal image)