Margriet Kwint

Safety and efficacy of reduced dose and margins 31 2 Results A total of 308 consecutive patients were included in this study with 170 patients in the reference-cohort and 138 patients in the reduction-cohort. The majority of the patients (70%) received cCRT in both cohorts. The median follow-up time was: 49 months (IQR 39-53) 48 months (IQR 42-57) for the reference-cohort and 21 months (IQR 15-27) 27 months (IQR 22-34) for the reduction-cohort, respectively. Twenty patients were excluded: 3 patients who received 60 Gy (EQD2 10 ) before June 2015 due to a high MLD (>20 Gy) and 17 patients who received 70 Gy (EQD2 10 ) to the mediastinum after June 2015. The reasons were: individually decided by clinician (n=5), inclusion of the hilar nodes within the primary tumour volume (n=7), by mistake (n=4) or treated within a study protocol (n=1). Patient and tumour characteristics are shown in Table 1 ; no significant differences were observed between the 2 cohorts, except T-stage: the patients with T0-X and T3 were unevenly distributed favouring the reference-cohort. However, the volume of the primary tumour was comparable. For both cohorts, the median GTV of the primary tumour was three-times larger than the GTV of the involved lymph nodes. The median radiation doses to the OAR are shown in Table 2 . Table 1 : Baseline patient and tumour characteristics in relative numbers (absolute numbers between brackets). Characteristic Reference (N=170) Reduction (N=138) Total N=308 P-value Median age (IQR) 65 (59-72) 65 (59-70) 65 (59-71) 0.192 Gender 0.188 Male 58.2% (99) 50.7% (70) 54.9% (169) Female 41.8% (71) 49.3% (68) 45.1% (139) Performance status 0.584 WHO 0 38.8% (66) 34.1% (47) 36.7% (113) WHO 1 53.5% (91) 59.4% (82) 56.2% (173) WHO 2 7.6% (13) 6.5% (9) 7.1% (22) T-stage T0-X T1 T2 T3 T4 7.6% (13) 15.9% (27) 27.1% (46) 12.9% (22) 36.5% (62) 1.4% (2) 16.7% (23) 24.6% (34) 26.1% (36) 31.2% (43) 4.9% (15) 16.2% (50) 26.0% (80) 18.8% (58) 34.1% (105) 0.008 0.012 0.853 0.630 0.003 0.337