S891
Clinical - Mixed sites & palliation
ESTRO 2026
motivation among centers to expand its use and to participate in prospective studies. These findings highlight the need for collaborative efforts to generate high-quality data and establish evidence-based guidelines supporting the safe and effective integration of HYPO-PBT. Keywords: hypofractionation, proton therapy, survey
patients/year with HYPO-PT, respectively. Figure 1 shows the number of centers using HYPO-PT for each reported cancer. The most frequent tumors PT resulted to be breast, sarcomas, and CNS. Conversely to adults, only 16.7% of the centers currently treat pediatric patients with HYPO-PT. In those centers this schedule is used in <10% of the pediatric population. Scientific evidence of efficacy and safety still lacking and radiobiological uncertainties were indicated as the main barriers to a further implementation of HYPO-PT in the daily clinical practice. All centers would like to expand the use of HYPO-PT, and 16/18 (94%) centers would be interested in participating in clinical studies, particularly in the setting of lung (10 centers), CNS (9 centers), and breast (8 centers) cancers. Six centers (33%) have currently at least one active study regarding HYPO-PBT. Figure 2 shows results regarding opinions on how improve the implementation of HYPO- PBT.
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Encouraging Clinical Outcomes from the First 20 Patients Treated with a Helical Lattice-VMAT Approach Enhancing Low-Valley Dose Reduction Santiago Velázquez-Miranda 1 , Beatriz Spa-Gómez 1 , Sara Delgado-Espinosa 1 , María del Carmen Fernández- Fernández 2 , Inmaculada Rincón-Pérez 2 , Javier Peinado- Serrano 2 , María Luisa Aguilar-Adame 2 1 Medical Physics, Virgen del Rocío University Hospital, Seville, Spain. 2 Radiation Oncology, Virgen del Rocío University Hospital, Seville, Spain Purpose/Objective: SFRT aims to exploit immune-mediated mechanisms through deliberate intra-tumoural dose heterogeneity. In our Lattice project, HelixRad, the helical vertex arrangement was optimized by VMAT using the negative margin technique (Kim et al., 2013), where MLC leaves are positioned slightly inside each vertex to reduce peripheral dose and deepen valleys, thereby enhancing the underlying biological rationale of Lattice radiotherapy (Amendola, 2020) while improving planning efficiency. V ₃ Gy [%] and V ₅ Gy [%] values calculated for the CorkGTV (GTV – [Vertices + 3 mm]), normalized to the number of vertices, were investigated as potential biomarkers of spatial heterogeneity. For simplicity, these normalized indices are referred to as cork3 and cork5, proposed as potential predictive markers. Material/Methods: Twenty patients with bulky, unresectable tumours (>5 cm, ECOG ≤ 2) were treated using single-fraction HelixRad (Dmin, vertex=12 Gy; Dmax, vertex ≈ 20 Gy; Dvalley<3 Gy). Vertices were arranged helically (135° rotation, pitch = vertex diameter + 2 mm). Planning was performed in Eclipse (Acuros XB), verified by 3%/1 mm gamma analysis, and treatment delivered on TrueBeam STx. Toxicity (CTCAE v5.0), quality of life (EORTC QLQ-C30), and imaging follow-up (CT/MRI) were evaluated for 6 months. Clinical responses were classified as withOUT_R (no response), With_R (pain relief with local volume reduction), or ABSCOPAL (systemic response outside the irradiated field).
Conclusion: This survey provides the first comprehensive overview of HYPO-PBT practices across Europe. There is strong
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