2.2.2. N1a/N1b-Subgroup Outcome Analysis

In the N1a/N1b-subgroup analysis, 154 patients were included (63 +mETE patients, 91 −mETE patients). In total, 113/154 (73.4%) patients presented with N1a-stage and 41/154 (26.6%) patients with N1b-stage. In patients with N1a-stage, a mean of 19 ± 13 lymph nodes was removed, and in patients with N1b, 30 ± 20 lymph nodes were removed (*p* = 0.001). There was no significant difference between the two groups in terms of Tg responder rates after stimulation (62% in +mETE patients (39/63) and 65% in −mETE patients (59/91), *p* = 0.710) and relevant iodine uptake in the whole body scan (92% in +mETE patients (58/63) and 87% in −mETE patients (79/91), *p*-value 0.307). Overall, responder rates in this subgroup also were comparable irrespective of mETE (59% in +mETE patients (37/63) and 57% in −mETE patients (52/91), *p*-value 0.845). All data regarding treatment success after follow-up are summarized in Table 2. Irrespective of mETE, in the N1a/N1b-subgroup, subgroup responder rates were significantly lower than in the N0/Nx-subgroup (59% versus 84% in +mETE and 57% versus 84% in −mETE patients, *p*-value 0.001, respectively). In Figure 1, responder rates for the entire group and N0/Nx- and N1a/N1b-subgroups are presented. No differences in responder rates of the entire group as well as among subgroups could be found, irrespective of the presence of mETE.

**Figure 1.** Responder rates (in %) of the entire group and the N-subgroup. No significant differences were found regarding responder rates in the entire group and among N0/Nx- and N1a/N1b-subgroups.

Of note, patients with N1a/N1b-status and+mETE received a significantly higher initial radioiodine activity as compared to patients from the −mETE group (6.3 ± 1.7 GBq versus 3.8 ± 1.1 GBq, *p*-value 0.001). In patients with higher administered RAI activity (≥7400 MBq), significantly more patients showed +mETE compared to patients with lower (≤3700 MBq) administered RAI activity (49/57 (86%) patients with high RAI activity versus 89/398 (22%) patients with low RAI activity, *p*-value 0.001). Furthermore, significantly more patients with higher administered RAI activity showed N1-stage (52/57 (91%) patients with high RAI activity versus 102/398 (26%) patients with low RAI activity, *p*-value 0.001). Significantly more patients with higher administered RAI activity showed poorer response rates compared to patients with lower administered RAI activity (25/57 (49%) patients with high RAI activity versus 88/398 (22%) patients with low RAI activity, *p*-value 0.001).
