Fig. 2

Schematic depiction of volumes. a Delineation of the initial GTV (GTVini), analysis volume GTV at recurrence/progression (GTVrt), and their intersection. b Schematic depiction of volumes. These volumes were postulated in order to identify regions within and adjacent to the initial GTV (GTVini, dark blue, dark blue outline) that might contribute to growth of recurrent tumor. GTV at recurrence (GTVrt, red margin) includes possible residual initial tumor tissue. Progression zone = new tissue without overlap with GTVini, green. Growth zone = 3 mm margin within the GTVini bordering on the progression zone (depicted in orange). Subclinical infiltration = GTVini + a 6 mm margin in all directions (depicted in turquoise). Initial CTV depicted in light blue, initial PTV in light grey. c Example of target volume and analysis volume evaluation in matched contrast enhanced T1 MR imaging showing recurrent tumor tissue, using colors corresponding to b. For clarity reasons, subclinical infiltration was omitted in this example