S834
Clinical - Lung
ESTRO 2026
delineation variability and corresponding margins of peripheral early stage NSCLC treated with stereotactic body radiotherapy. Radiother Oncol. 2015 114(3):361- 6. Keywords: Subclinical disease, SABR, Internal target volume
dose CTV increased TCP by 4.4(3.1)% over the ITV approach while increasing the mean lung dose by 1.0(0.3)Gy. Importantly, the CTV approach only added dose in the cranio-caudal direction, as its prescription dose remained below existing dose gradients in the axial plane (Fig.1). The fitted model calibrated well (Fig.2b) and showed on average 1.2 SDDs, 37% SDD presence at 0.9 times the equivalent GTV radius, and clonogen density of 0.5*107 cm-3 (Brier score: 0.102, p=0.003). Conclusion: For the first time, a subclinical disease model was fitted directly to radiotherapy outcome data. The model accurately predicts observed locoregional recurrence rates, showing that ITV-based planning contributes somewhat to control of SDDs. However, replacing the ITV with a low-dose CTV strategy promises better control of subclinical disease, with only modest increase in mean lung dose. External model validation is in progress.
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GTV-based prescription in lung SBRT: Tumour dose consistency and local control in a single-institution interim analysis Volha Hertsyk 1 , Thomas Lacornerie 2 , Raffaella De Pietro 1 , Bryan Leurquin 1 , Nicolaus Andratschke 3 , Enrico Clementel 1 , Maria Chiara Lo Greco 4,5 , Florence Le Tinier 6 , Nick Reynaert 7 1 Headquarters, EORTC, Brussels, Belgium. 2 Department of Medical Physics, Centre Oscar Lambret, Lille, France. 3 Department of Radiation Oncology, University Hospital Zürich, Zürich, Switzerland. 4 QUARTET Project, European Society for Paediatric Oncology (SIOP Europe), Brussels, Belgium. 5 Faculty of Medicine and Health Sciences, University of Ghent, Ghent, Belgium. 6 Department of Radiation Oncology, Centre Oscar Lambret, Lille, France. 7 Medical Physics Department, Institut Jules Bordet, Hôpital Universitaire de Bruxelles,, Brussels, Belgium Purpose/Objective: In lung stereotactic body radiotherapy (SBRT), dose is commonly prescribed to the PTV. In line with the ACROP/ICRU 911, standardization of dose reporting is essential. Central (tumour-based) dose correlates more strongly with Local Control (LC) as demonstrated by Eriguchi (2022)2, that may support the idea of GTV- based prescription in lung SBRT. The aim of this work is to report real-world data on (i) how closely Dmean(GTV) tracks the nominal prescription, and (ii) whether it reflects on LC rates. Material/Methods: Patients treated with lung SBRT for pulmonary lesions (mixed primary/metastatic) from 2016-2021 at a single institution were retrospectively reviewed. Delineation was performed on an end-exhale CT (either from 4DCT or breath-hold scan acquired near natural exhalation). The dose was prescribed to the Dmedian(GTV) with intrafraction tumour tracking for all targets. Plans were optimised using Ray-Tracing for uniform fluence through the PTV (GTV+5mm) and recalculated with Monte Carlo to account for secondary electron transport in lung heterogeneities. GTV and PTV volumes, mean doses, and prescription doses were recorded and reported as Biologically Effective Dose (BED ₁₀ , α / β = 10 Gy). LC was assessed by follow-up (FU) imaging records and compared to literature-reported rates. Only lesions with at least one post-RT imaging
References: 1: Apolle et al. The clinical target volume in lung, head- and-neck, and esophageal cancer: Lessons from pathological measurement and recurrence analysis. Clin Transl Radiat Oncol. 2017 21;3:1-8; 2: Peulen et al. Mid-ventilation based PTV margins in Stereotactic Body Radiotherapy (SBRT): a clinical evaluation. Radiother Oncol. 2014;110(3):511-6; 3: Webb, Nahum. A model for calculating tumour control probability in radiotherapy including the effects of inhomogeneous distributions of dose and clonogenic cell density. Phys Med Biol. 1993 Jun;38(6):653-66; 4: Peulen et al. Target
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