S2238
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
Sebastiano Menna 2 , Elisa Pilloni 2 , Martina Iezzi 1 , Alessia Re 3 , Althea Boschetti 1 , Sami Aburas 1 , Antonio Piras 1 , Carmela Di Dio 1 , Anna Bruynzeel 4 , Luca Boldrini 5 , Jonathan Leeman 6 , Gian Carlo Mattiucci 1 , Davide Cusumano 2 1 Radiotherapy Unit, Mater Olbia Hospital, Olbia, Italy. 2 Medical Physics Unit, Mater Olbia Hospital, Olbia, Italy. 3 Radiotherapy Unit, Azienda USL-IRCCS Reggio Emilia, Reggio Emilia, Italy. 4 Radiotherapy Unit, VUMC, Amsterdam, Netherlands. 5 Radiotherapy Unit, Fondazione Policlinico Gemelli IRCCS, Rome, Italy. 6 Radiotherapy Unit, Dana Farber Cancer Institute, Boston, USA Purpose/Objective: The thorax presents unique challenges in radiotherapy: although stereotactic ablative radiotherapy (SABR) achieves high local control in NSCLC and pulmonary metastases, further improvements are desirable, particularly dose escalation in radioresistant metastases and planning target volume (PTV) margin reduction to minimize toxicity. Full online adaptive Magnetic Resonance Imaging-guided Radiotherapy (MRIgART) supports these strategies by ensuring daily dose accuracy through compensation of Electron Density (ED) variations. However, prolonged treatment times remain the main obstacle to clinical implementation. To address this limitation, we introduce Adaptive Skin Radiotherapy (ASRT), a time-efficient MRIgART workflow designed to maintain accuracy while Lung patients undergoing MRIgART were prospectively enrolled and treated with a biologically effective dose (BED) higher than 100 Gy. Gross tumor volume (GTV) was delineated on simulation MRI co-registered with staging CT, and PTV was created by isotropically expanding GTV by 3 mm. ASRT involves a rapid online workflow where only body contour and target are recontoured, minimizing changes to organs at risk (OARs). Physicists update the electron density map to reflect anatomical changes, recalculating the predicted plan using original beam fluence and re-optimizing it to meet clinical goals. Plans followed ICRU91 guidelines with an isodose line near 80%. Dose differences between predicted, adapted, and original plans were analyzed for target coverage and OARs. Treatment duration and toxicity were recorded. Survival outcomes were assessed using Kaplan-Meier analysis. Results: A total of 41 patients were enrolled, receiving 232 fractions, of which 178 (76.7%) were treated with ASRT. Online adaptation significantly improved target coverage (median V100% change: +0.1%±2.5%) compared to predicted plans ( − 2.6%±7.3%, p<0.001), enhancing feasibility. Material/Methods:
Results: Eight out of the ten participants completed the evaluation for the full duration of 90 minutes on the MRI platform, reporting a median discomfort score of 5.0 (IQR 4.0-6.0). The head, sternum and shoulders were the most frequently mentioned areas of discomfort. All ten participants were able to hold the prone position for the full 90 minutes using the new immobilization platform, with a median discomfort score of 4.5 (IQR 2.3-5.0) (Figure 2A). Immobilization results with the MR imaging platform showed nipple displacements up to 9 mm, while the nipple displacements with the new immobilization platform up to 8 mm (Figure 2B).
Conclusion: The new platform was associated with improved comfort, and all volunteers completed the 90-minute evaluation without interruption. However, a notable reduction in breast displacement was not found. This work presents initial groundwork to improve patient comfort and enhance the design of novel devices for hyperthermia. Keywords: Patient comfort, immobilization, hyperthermia
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Adaptive Skin Radiotherapy (ASRT): clinical and dosimetric outcomes of a new time-efficient MRI- guided workflow for lung lesions Francesco Catucci 1 , Lana Smiljanic 1 , Francesco Preziosi 1 , Luca Vellini 2 , Flaviovincenzo Quaranta 2 ,
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