Systematic Lymph Node Mapping for Radiation Therapy

To allow a systematic topographic mapping of the lymph node locations, the cross-sectional nodal atlas published by Martinez-Monge et al. was used [7 (link)]. For each patient the number and location of the affected, PET-positive lymph nodes were documented. Beyond summarizing these data in a table, each single PET-positive lymph node was manually contoured in a “virtual” patient dataset to achieve a 3-D visualization of the cumulative PET positive lymph node distribution (Fig. 1a and b). The Oncentra MasterPlan (Version 4.3, Elekta, Crawley, UK) planning system was used for contouring and generating 3-D images for the atlas. Moreover, the PET-positive lymph node location in each patient was assessed with regard to the existence of a potential geographic miss (i.e. PET-positive lymph nodes that would not have been treated adequately by the RTOG consensus on clinical target volume definition of pelvic lymph nodes [5 (link)]).Fig. 1

a Distribution and geographic miss according to RTOG – CTV (red) of PET positive lymph nodes in patients with no prior treatment (n = 32); b Distribution and geographic miss according to RTOG – CTV (red) of PET positive lymph nodes in postoperative patients (n = 87)