ESTRO 2023 - Abstract Book

S115

Saturday 13 May

ESTRO 2023

Secondary endpoints were local control (LC), disease free (DFS) and overall survival (OS). Logistic regression, spearman correlation and Kaplan Meir analysis were used to identify effects of lymphopenia on endpoints Results Database review identified 102 patients eligible for inclusion. Patient and treatment characteristics are presented in table 1. Median lymphocyte nadir was 535 (IQR 380-730) categorized as grade 2 (n=37, 36%), grade 3 (n=42, 41%) and grade 4 (n=4, 4%) and occurred during the final 2-weeks of n-CRT. Although lymphocyte count recovered before surgery, rebound lymphopenia (median 400 IQR 300-540) occurred upon surgery. Spearman analysis suggested lymphocyte count decreased as tumor volume increased (rho -0.1, p=0.36) and (fig.1A). Use of either VMAT or 3DCRT techniques did not change this relationship (fig. 1B). Yet, use of deep inspiratory breath hold (DIBH) technique changed the effect of tumor volume (fig.1C p=0.05). No other variables correlated with lymphopenia, including dosimetric variables (fig.1D-G).

MPR was recorded in 31/48 (64.6%) with lymphopenia grade ≥ 3 vs. 36/54 (66.6%) for grade ≤ 2 (OR 1.1 p=0.82). PCR was recorded 18/48 (37.5%) with lymphopenia grade ≥ 3 vs. 20/54 (37%) for grade ≤ 2 (OR 1.02, p=0.96). Mean residual tumor cells did not correlate with lymphocyte count (rho 0.01, p=0.9). The MRTC was 14% (SD21) for grade 0-2 vs. 19% (SD28) for grade 3-4 lymphopenia p=0.6 (fig 2A-B). Although LC was improved with lymphopenia (HR 0.28, p=0.03), DFS (HR 0.86, p=0.6) and OS (HR 0.9, p=0.6) were unaffected by lymphopenia (fig.1C-E).

Conclusion Lymphopenia grade ≥ 3 during n-CRT occurred in 45% of patients, was correlated with tumor volume in treatments delivered in free breathing but not in breath hold. Although lymphocyte count recovered, following surgery, rebounded lymphopenia was observed. Contrary to our hypothesis, lymphopenia during n-CRT did not correlate with pathologic regression and did not impair DFS and OS. PD-0154 Dosimetric analysis of bronchial tree to assess toxicity-risk in SBRT of ultracentral lung tumors M. Ahmadsei 1 , V. Jegarajah 1 , R. Dal Bello 1 , S.M. Christ 1 , M.M. Mayinger 1 , L.S. Stark 1 , J. Willmann 1 , I.R. Vogelius 2 , P. Balermpas 1 , N. Andratschke 1 , S. Tanadini-Lang 1 , M. Guckenberger 1 1 University Hospital Zurich, Department of Radiation Oncology, Zurich, Switzerland; 2 Rigshospitalet, University of Copenhagen, Department of Oncology, Copenhagen, Denmark

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