ESTRO 2025 - Abstract Book

S1413

Clinical - Lung

ESTRO 2025

Conclusion: Our data shows similar OS in no-comorbidity patients treated with SBRT compared to surgery. In patients with low or high comorbidity, surgery resulted in better OS. However, SBRT patients required more hospital admissions prior to cancer diagnosis, suggesting a high fragility in this group. The CCI may not be an accurate method to discriminate between surgical and non-surgical patients. So, a new score for our population is needed for individualizing treatment decisions based on patient characteristics and comorbidities.

Keywords: NSCLC, SBRT, comorbidity

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Digital Poster ITV-PTV margin reduction from 5 to 3 mm for SBRT-lung treatment

Rana Altayan, Saskia Treur, Chin L Ong, Eric Franken Radiotherapy, HagaZiekenhuis, The Hague, Netherlands

Purpose/Objective: When using an ITV (Internal Target Volume) approach for SBRT (stereotactic body Radiotherapy treatment) of Non Small-Cell lung cancer (NSCLC) patients, many institutes use a 5 mm ITV-PTV (planning target volume) margin. Bellec et al. (1) suggests that a 3 mm margin is sufficient, based on GTV (gross tumor volume) delineation on 4D-CBCT (cone-beam computed tomography) images acquired during treatment. This study examines the validity of this claim through visual analysis of the GTV position in pre- and post-treatment 4D-CBCT images. Material/Methods: 29 NSCLC patients (aged 63-88) with peak-peak tumor breathing amplitude of >8mm were included in this study. The patients were treated with fractionation schemes of 3x18 Gy (39%) and 5x11 Gy (61%) and the tumors were located in the lower (80%) and upper (20%) lobe. Treatment planning was done in RaySearch on the average 4D-CT dataset for Elekta Versa HD linac. Both pre- and post-treatment 4D-CBCT’s, acquired using the Elekta XVI system, were analysed using an additional contour ITV+3mm to facilitate the analysis. Table 1 presents the scoring matrix of the overall treatment quality for each patient, based on a visual inspection of the tumor in all post-treatment breathing phases of the (unmatched) CBCT images of all fractions.

Results: Figure 1 shows the results for a single patient, with examples of the most cranial tumor-position being within (panels A and C) and outside the ITV+3mm contour (panel B). Analysis of the pre-treatment CBCT images after