fig1

Figure 1. Target volume transformation. Nodal target volume transformation is defined as “upgrading” lymph node metastasis from the elective CTV to GTV based on their increased detectability resulting from improved diagnostic imaging techniques. Target volume transformation may result in overtreatment of both volumes. First, the boost-dose is now prescribed to small lymph node metastases that would have traditionally been treated with the elective dose. Second, the traditional elective dose is prescribed to the elective CTV while the occult tumor volume within the elective CTV is decreased as a result of improved diagnostic imaging (A). By refining traditional binary dose prescription to a gradient dose prescription that is proportional to (occult) tumor volume, the current overtreatment can be addressed in order to decrease treatment-related morbidity without compromising efficacy (B). Reprinted from van den Bosch et al.^[29], with permission from Elsevier. CTV: Clinical target volume; GTV: gross tumor volume.