Fig. 1.

Schematic of sphere arrangement in PTV_6670 (orange) and PTV_Avoid (blue). Spheres are 1.5 cm in diameter and arranged on vertices of a square 3 cm grid oriented on axial slices of the CT acquisition. HDS spheres must be placed diagonal to each other and be confined within a GTV retraction (magenta). LDS are placed on vertices adjacent to the HDS and must be confined within PTV_2000 (cyan). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)