ESTRO 2023 - Abstract Book

S1067

Digital Posters

ESTRO 2023

Purpose or Objective Stereotactic ablative radiotherapy (SABR) of ultracentral lung tumors (ULT) carries an increased risk for overdoses inside sensitive mediastinal organs with potentially severe late-onset bleedings. Hence, ultracentral location is discussed as residual “No Fly Zone”. We apply stereotactic magnetic resonance-guided online adaptive RT (SMART) to treat ULT because daily online plan adaptation can protect sensitive mediastinal organs. Here, we describe long-term outcomes after SMART of ULT. Materials and Methods 36 patients with 40 lung tumors received SMART inside a prospective database. 16 tumors were deemed ultracentral due to contact with the proximal bronchial tree (type A: 7, type B: 4) or esophagus, 20 patients with non-ULT (24 lesions) served as comparison group. SMART was delivered on an 0.35 Tesla MR-linac (MRIdian®, ViewRay Inc.) (Figure 1). Usually, ULT received 10 x 5-6 Gy, while non-ULT received 8 x 7.5 Gy (central) or 5 x 10 Gy (peripheral).

Figure : SMART of an ultracentral lung metastasis. Left : Baseline plan with planning target volume (PTV: red), esophagus (yellow) and main stem bronchi (dark blue). Middle : Prediction of the baseline plan on the daily anatomy of fraction 7 shows dose declines at the PTV borders (white arrowheads), while the right main bronchus receives an overdose (white arrow). Right : Plan adaptation maintains the PTV coverage and avoids overdoses in the main bronchus. Results ULT were larger than non-ULT (median PTV: ULT 54.7 cm ³ , non-ULT 19.2 cm ³ ), otherwise baseline characteristics were balanced between the groups. ULT (N = 16) non-ULT (N = 20) Median [IQR] Median [IQR] Age [years] 65 [55- 72] 65 [60 – 76] KPI [%] 90 [80 – 90] 80 [80 – 100] FEV1s [%] 65 [52 – 81] 69 [59 – 87] Sex After a median follow-up of 20.4 months, overall survival (OS) was similar between ULT and non-ULT (2-year OS: ULT 67%, non-ULT 60%, p = 0.71). Local tumor control (LC) was favorable, with only one local tumor progression of an ULT (2-year LC: ULT 92%, non-ULT 100%, p = 0.26). Treatment of ULT led to significantly more toxicities ≥ grade 2 (ULT: 9/16 (56%), non-ULT: 1/20 (5%), p = 0.002). Toxicities were mainly moderate (grade 2), but included three high grade toxicities ≥ grade 3 in ULT: One patient developed an esophagitis grade 3 and a late bronchial bleeding grade 4 in the context of treatment with a vascular endothelial growth factor (VEGF) inhibitor. Another patient experienced an unclear late bronchial bleeding grade 3. No treatment-related death was observed. Conclusion SMART enables effective treatment of ULT. Compared to “conventional” non-adaptive techniques, SMART has the potential to reduce severe complications when combined with risk-adapted fractionation schemes (10 x 5 - 6 Gy). Still, ablative treatment of ULT remains a high-risk procedure and needs careful benefit-risk-assessment (tumor , VEGF inhibitors). E. Kneepkens 1 , J. van der Stoep 1 , A. Vullings 1 , J. Buck 1 , M. Velders 1 , M. Öllers 1 , L. in 't Ven 1 , J. van Loon 1 , D. de Ruysscher 1 , S. Peeters 1 1 Maastricht University Medical Centre+, Department of Radiation Oncology (MAASTRO), GROW School of Oncology, Maastricht, The Netherlands Purpose or Objective Reducing breathing motion through inspirational breath hold (IBH) could benefit both proton and photon therapy of lung tumors, as it allows for margin reduction and leads to a larger lung volume compared to free breathing (FB) treatments. For protons, IBH would also mitigate the interplay effect. In this study, we compared proton and photon FB and IBH plans in terms of their dosimetric differences and normal tissue complication probability (NTCP). M: 9 (56%) F: 7 (44%) M: 11 (55%) F: 9 (45%) Oncological situation Oligometastasis: 12 (75%) Early NSCLC: 4 (25%) Oligometastasis: 14 (70 %) Early NSCLC: 6 (30%) PO-1334 Breath hold for photon or proton therapy in radical radiotherapy for lung cancer: worth the effort?

Materials and Methods