ESTRO 2022 - Abstract Book

S382

Abstract book

ESTRO 2022

Results 210 consecutive pts were screened and 169 pts were included (IMPT: n = 35, IMRT: n = 134). Median age was 66 years, 53.3% were male, 40.8% had a squamous NSCLC and 41% of pts had a WHO Performance Status (PS) =0. Median Gross Tumor volume (GTV) was 70.4 cm 3 . No differences in age, gender, baseline PS, GTV and tumor histology were noted between IMPT and IMRT. 98.2% of the pts received a RT dose of 60-66Gy. 46.2% of IMPT treated pts and 75% IMRT treated pts developed lymphopenia G ≥ 3 (Odds Ratio [OR]: 3.5, 95% CI 1.1-12.1, p=0.042). Including age, comorbidities, chemotherapy regimen, gender, disease stage (IIIA vs. IIIB/IIIC) and GTV in the multivariate analysis, IMPT confirmed to be associated with less lymphopenia (OR: 0.07, 95% CI: 0.01-0.54, p=0.01). Neutropenia G ≥ 3 occurred in 62% and 68% in IMPT and IMRT treated pts respectively (p=0.51). This was 31% and 29% respectively for febrile neutropenia (p=0.74). Bone marrow RVs were associated with a higher risk of lymphopenia G ≥ 3 (V4, V5, V10 and V20, with a significance level of 0.05, 0.034, 0.023, and 0.026 respectively). IMPT was also associated with a lower rate of PS ≥ 2 at day 21 (OR: 0.3, 95% CI 0.1-0.95, p=0.042) (table 1) .

Conclusion IMPT reduces the incidence of lymphopenia G ≥ 3 in pts with stage III NSCLC treated with CCRT, due to lower bone marrow RVs. In addition, IMPT led to a faster PS recovery after CCRT, thus potentially increasing the number of patients eligible for adjuvant durvalumab.

OC-0439 Geometric and dosimetric stability of high FDG-uptake volumes during dose escalated RT of NSCLC

D.S. Møller 1 , L. Hoffmann 1 , A. Haraldsen 2 , M.M. Knap 3 , A.A. Khalil 3 , C.M. Lutz 1

1 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Nuclear Medicine & PET-Centre, Aarhus, Denmark; 3 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark Purpose or Objective In the multi-centre phase III trial NARLAL2 (NTC NCT02354274) locally advanced NSCLC patients are randomised between a homogenous dose to the entire target (66Gy/33fx) and a heterogeneous dose escalation driven by the high FDG-uptake volumes (mean doses up to 95Gy/33fx). In this study, we investigate the geometric and dosimetric stability of these volumes. Materials and Methods In total, 68 patients were included. They all had three repeated PET/CT scans at the same scanner: PET/CT0 (2 weeks before RT start, used for planning), PET/CT1 (1 week after RT start) and PET/CT2 (2 weeks after RT start). The GTV of the primary tumour was delineated on each scan. Within each GTV, the sub-volume with FDG-signal above a threshold of 50% of SUVpeak was segmented (V0, V1 and V2). CT1 and CT2 were rigidly registered to CT0 prioritizing the GTV area. The overlap fraction (OF) was defined as: OF 0X =(V0 ∩ VX)/min(V0,VX), X=1,2. Regardless of randomisation result, the dosimetric impact of changes in FDG uptake was investigated by recalculation of the escalated dose plan on CT2 (with V2). The