ESTRO 2026 Congress Report
By the SFRT ESTRO Focus group
SUMMARY
ESTRO 2026 in Stockholm, Sweden, brought remarkable momentum to the field of Spatially Fractionated Radiotherapy (SFRT). Over five days, there were proffered paper sessions, poster discussions/highlights, symposia, and a well-attended SFRT Meet & Greet event with an estimated 80 participants. Key themes included novel radiobiological and immunological mechanisms of minibeam (MBRT) and microbeam radiotherapy (MRT), clinical outcomes of lattice, international practice pattern surveys, advances in treatment planning and dose calculation, and translational perspectives on FLASH-MBRT combinations. This report compiles all SFRT-relevant presentations and posters from the congress.
Sessions covered: 2 proffered paper presentations · 5 poster discussion/highlight sessions · 1 symposium · 1 pitch session · 1 Meet & Greet · 25 total posters
Saturday, 16 May · 10:30–11:30
Proffered Papers: Biology of Novel Irradiation Techniques
Chairs: Rob Coppes (The Netherlands) · Elke Beyreuther (Germany)
Presentation 1 - Meihua Chen (China)
"MBRT Combined with Bevacizumab Unlocks Anti-tumour Immunity via ICAM1/LFA1-Mediated CD8+ T Cell Infiltration"
Dysfunctional tumour vasculature is a critical barrier to effective cancer immunotherapy by blocking CD8+ T cell infiltration. This study explored how minibeam radiation therapy (MBRT) combined with bevacizumab (angiogenesis inhibitor) can overcome this barrier.
Methods: Murine tumour models were used to assess vascular parameters, endothelial ICAM1 expression, and tumour-infiltrating CD8+ T cells (quantified by flow cytometry) after combined MBRT (0.6-mm beam spacing, 0.6mm; peak dose 150Gy) and bevacizumab.
Key Results: Combination therapy yielded ~2× increase in pericyte coverage, ~40% reduction in vascular permeability, and ~2× increase in CD8+ T cell infiltration (42.3% vs. 20.4% in controls). Upregulation of ICAM1 and enhanced LFA1 expression on infiltrating T cells were key mediators. CD8+ T cell depletion fully abrogated the therapeutic effect.
Conclusion: MBRT and bevacizumab synergistically remodel the tumour microenvironment through vascular normalisation and ICAM1-LFA1 axis amplification, providing a rationale for radio-immunotherapy combinations targeting this pathway.
Presentation 2 - Verdiana Trappetti (Switzerland)
"Microbeam Radiotherapy Shows Promise for Metastatic Triple-Negative Breast Cancer: Insights from a Dose-Escalation Chick Embryo Study"
This study assessed MRT's ability to control triple-negative breast cancer (TNBC) and suppress metastatic spread - the primary driver of TNBC mortality - using a chick embryo chorioallantoic membrane (CAM) human xenograft model.
Methods: MDA-MB-231 TNBC xenografts were treated at ESRF with escalating MRT doses (2–10 Gy valley / 152–761 Gy peak). Primary tumour control, metastatic burden in lower CAM/liver/lung/brain, and RNAseq analyses were performed.
Key Results: 100% embryo survival at 2–6 Gy valley doses. Dose-dependent reduction in proliferation, statistically significant at 8–10 Gy valley. Decreased metastatic burden in all organs vs. controls, most pronounced in the liver and brain. RNAseq revealed dose-dependent activation of cancer cell death genes and modulation of EMT pathways.
Conclusion: First evidence that MRT controls both primary TNBC and metastatic spread. Results support further investigation of MRT in metastatic TNBC.
Saturday, 16 May · 15:15–16:15
Poster Discussions: Mixed Clinical Sites
Chairs: Gitte Fredberg Persson (Denmark) · Łukasz Kuncman (Poland)
Presentation 3 - Rocco Mottareale (Italy)
"Spatially Fractionated Radiotherapy (SFRT) for Bulky Tumours: A Systematic Review of Clinical Outcomes and Dosimetric Variability"
A systematic review assessing the clinical evolution, efficacy, safety, and dosimetric characteristics of SFRT (GRID and lattice radiotherapy) for bulky/radioresistant tumours.
Methods: MEDLINE search (Jan 2010–Jun 2025) using terms: 'Spatially Fractionated,' 'lattice,' 'GRID,' 'radiotherapy.' 27 studies, 363 patients, 468 lesions analysed.
Key Results: Most common sites: thorax (37.8%), abdomen (16.7%). Predominant histologies: sarcoma (34.4%), non-small cell lung cancer (NSCLC) (15.7%). Majority palliative intent. Tumour regression in ~80% of lesions, mostly Grade 1-2 toxicity. Valley-to-peak dose ratio (VPDR) ranged 0.04-0.30 (high heterogeneity) and 0.23-0.25 (moderate). Median vertex tumour volume (VTV) 2.7 cc; vertex diameter 1.2 ± 0.2 cm; centre-to-centre spacing 3.8 ± 1.1 cm.
Conclusion: SFRT is safe and feasible for bulky tumours with promising palliation and local control. Standardisation of VPDR and dosimetric reporting is urgently needed.
Sunday, 17 May · 10:30–11:30
Poster Discussions: Access, Economics and Innovation in Radiation Oncology
Chairs: Filipe Moura (Portugal) · Aileen Flavin (Ireland)
Presentation 4 - Dora Correia (Switzerland)
"Spatially Fractionated Radiotherapy Practice Patterns – an EORTC-ESTRO SFRT Focus Group Survey"
The first large-scale international survey characterising current SFRT clinical practices, education, and implementation barriers across 39 countries.
Methods: Four-section online questionnaire distributed Jun-Oct 2025 via EORTC, ESTRO, and social media to radiation oncology professionals. n=130/154 respondents completed (39 countries, 4 continents).
Key Results: 60% currently use SFRT clinically; estimated >900 patients treated. Main indications: bulky tumours (68%), intra-abdominal metastases (40%). Predominantly palliative use (87%), also curative (32%), and re-irradiation (63%). Most common techniques: Lattice (32%), multi-leaf collimator (MLC)-GRID (13%), stereotactic body radiotherapy (SBRT) partial tumour irradiation of hypoxic segment (PATHY) (12%). 88% lacked formal SFRT training. 81% interested in multi-centre trials. Main barriers: lack of guidelines (71%), institutional support (54%).
Conclusion: SFRT adoption is growing but highly heterogeneous. Standardised guidelines, structured education, and collaborative trials are urgently needed.
Sunday, 17 May · 12:55–13:25
Meet & Greet: Spatially Fractionated Radiotherapy | Chairs: Slavisa Tubin
Meet & Greet – ESTRO SFRT Focus Group
The SFRT Meet & Greet session proved exceptionally successful, attracting an estimated 80 participants across all radiation oncology disciplines. Chair Slavisa Tubin and representatives Monica Serban, Sean Park, as well as Dora Correia and Verdiana Trappetti (as SFRT social media ambassadors) engaged with attendees.
The volume of questions and the level of international interest were remarkable, with discussions overflowing into the hallway after the session. During the Q&A session, participants discussed technical aspects of SFRT, including dosimetry and sphere placement for lattice therapy, and sought guidance on the first implementation at their sites. An upcoming programme for implementing SFRT in low- and middle-income countries was mentioned. Additionally, there was a question about strategies to convince clinicians to adopt SFRT.
Many international colleagues, already practising SFRT or about to embark on the project at their own institutions, expressed intent to join the SFRT Focus Group, promising an expanding network and growing collaborative dataset.
Sunday, 17 May · 16:30–17:00
Poster Highlights: Mixed Sites & Palliation
Poster Highlight - Slavisa Tubin (Austria)
"Overcoming Palliation by Single Ultra-High-Dose Partial Irradiation of Complex Bulky Tumours Allied with Immune-Targeted Therapy: First-in-Human Data"
This report presents the first clinical implementation of combined ultra-high-dose partial tumour irradiation (PTI) and immuno-targeted therapy as a last-resort strategy to convert declared palliative, conventionally untreatable disease into potentially curative treatment.
Methods: 6 patients with melanoma, hepatocellular carcinoma (HCC), NSCLC, small cell lung cancer (SCLC), and myxofibrosarcoma, previously progressing on systemic therapies, were treated May-November 2025. Primary eligibility: no remaining standard-of-care options due to tumour size/volume, location, or extensive contact with surrounding organs. Dose prescription: single fraction 20-24 Gy at 70% isodose to the central tumour segment (gross tumour volume (GTV) contracted by 8-10 mm). Tumours were highly aggressive, symptomatic, fast-growing, with a diameter >6 cm (range 6-12 cm). The same previously failed immuno- or targeted therapy was continued ≥7 days after PTI.
Key Results: Restaging computer tomography (CT)/magnetic resonance imaging (MRI) available for the first 4 patients (mean follow-up 4 months, range 2-6). Three of 4 patients - with HCC, SCLC, and melanoma - responded with 65%, 85%, and 100% tumour volume reductions, respectively. Disease status at last follow-up: regression. The fourth patient (myxofibrosarcoma) showed pseudo-progression at 6 weeks (swollen, widely necrotic-colliquative tumour). The SCLC patient presented two lymph nodal abscopal effects before immunotherapy was initiated. Side effects: G2 nausea (retroperitoneal melanoma), G1 pain (chest wall myxofibrosarcoma); 4 patients had no side effects.
Conclusion: Single-fraction PTI combined with immuno-targeted therapy was feasible and safe with minimal side effects not affecting quality of life. Fast symptom relief and strong neoadjuvant effect observed, with potential to convert unresectable disease to resectable. Abscopal effects confirm the immunomodulatory potential of this technique. Follow-up remains short, and the cohort is small.
Monday, 18 May · 10:30–11:30
Poster Discussions: Radiobiology | Chairs: Paul Span (The Netherlands) · Sona Michlikova (Germany)
Presentation 5 - Thomas Schmid (Germany)
"Minibeam Radiation Therapy (MBRT) Induces Mild Hyperactivity with Limited Acute Neurotoxicity in Mice"
This study characterised acute and subacute neurobehavioral effects of whole-brain MBRT compared to conventional broad beam (BB) irradiation, an important safety consideration for clinical translation.
Methods: C57BL/6 mice irradiated at FRM II (Garching, Germany) using the Line-Focus X-ray Tube (LFxT). MBRT: 260 µm beams, 1119 µm apart (PVDR=10, 15 Gy valley-150 Gy peak dose). Open field, Y-maze, and acoustic startle tests at 7, 30, 60, and 90 days post-treatment.
Key Results: At day 7: anxiety-like behaviour (fewer centre entries, prolonged Y-maze exit latency). Over 90 days: mild sustained hyperactivity (p≤0.01). No significant cognitive or sensorimotor deficits. Overall, neurotoxicity was markedly less than for conventional BB irradiation.
Conclusion: Whole-brain MBRT produces limited neurobehavioral toxicity despite high peak doses. Results support clinical translation, especially at doses expected to be lower than the equivalent uniform dose (EUD) used in this study.
Monday, 18 May · 15:15–16:30
Pitch Session: Biology-Driven Innovations in Radiotherapy: Identifying Techniques with the Strongest Clinical Impact | Chairs: Laura Patricia Kaplan (Denmark) · Line Kristensen (Denmark)
Pitch - Niels Bassler (Denmark)
"Spatial Fractionation in Radiotherapy: Translational Perspectives" - a pitch presentation surveying the landscape of SFRT from preclinical data to clinical implementation, framing translational challenges and opportunities.
MBRT was the focus of his presentation as he identified it as having the strongest potential clinical impact in the near future. His work showed that MBRT achieved a drastic gain in terms of toxicity reduction in in vivo animal models, compared to conventional radiotherapy (ConvRT) and FLASH-RT as well. MBRT could be indicated for recurrent tumours, radiation-resistant tumours and paediatric patients.
Monday, 18 May · 17:00–18:00
Poster Discussions: Innovation in Treatment Planning 2
Chairs: Tiago Ventura (Portugal) · Igor Bessieres (France)
Presentation 6 - Liam Day (Germany)
"A Fast Monte Carlo Engine for Microbeam Radiotherapy Dose Calculation"
MRT dose calculation has been limited by extremely long simulation times. This work presents a graphics processing unit (GPU)-accelerated Monte Carlo (MC) engine that brings calculation times within clinical feasibility.
Methods: Custom MC engine using Geant4 v11.3.0 Livermore physics models, ported to GPU (NVIDIA RTX A5000). Integrated with the Eclipse treatment planning system (TPS) v16.1 via algorithm application programming interface (API). Extended to compute dose-to-medium (Dm), dose-to-water (Dw), and dose-to-marrow/tissue (Dt).
Key Results: Central processing unit (CPU) engine: ~16× faster than hybrid-Geant4. GPU engine: ~26× faster than CPU (~420× vs. hybrid-Geant4). GPU calculation: ~5 min/field vs. ~36 hours for hybrid-Geant4. Dt better approximates soft tissue dose in bone than Dw, avoiding dose enhancement artefacts.
Conclusion: GPU-accelerated MC engine opens the door to inverse planning for MRT. A critical milestone toward clinical implementation.
Tuesday, 19 May · 09:15–10:30
Symposium: Think Immunomodulation, Maximise Outcome
Chairs: Anna Donaubauer (Germany) · Christopher Jones (United Kingdom)
Symposium Lecture - Slavisa Tubin (Austria)
"The Potential Synergy Between SFRT and Immunotherapy"
Radiation is a dual immunomodulator, and the stimulation or suppression of immune responses depends on dose, volume, technique, and tissue irradiated. Conventional large-volume RT tends toward immunosuppression. By contrast, SBRT and SFRT – delivered to smaller volumes in fewer fractions -spare peritumoural microenvironment and lean toward immunostimulation.
This lecture synthesised existing evidence on radiation-immune interactions, with emphasis on SFRT techniques. SFRT's unique radiobiological profile - inducing bystander effects, vascular normalisation, and immune activation – makes it especially relevant for bulky, hypoxic, radioresistant tumours that conventional RT cannot adequately address. The neoadjuvant and immunomodulatory potential of SFRT may represent a paradigm shift in the management of these complex clinical scenarios.
Selected Posters
The following SFRT-relevant posters were presented digitally, representing active research contributing to the field.
Poster 1 A novel SFRT strategy based on VMAT and CyberKnife synergy
First author: Yi Peng et al. (China)
Purpose: Address the trade-off between CyberKnife's superior PVDR and its impracticality for large GTVs (>250 cc, >60 min treatment time). CyberKnife treats lattice points; volumetric modulated arc therapy (VMAT) provides low-dose GTV coverage.
Results: Hybrid approach: PVDR 2.87 ± 0.28; average dose ratio (ADR) 2.16 ± 0.32; treatment time <60 min for large tumours. Outperformed VMAT alone in dose distribution while controlling delivery time.
Conclusion: The hybrid strategy is clinically feasible and dosimetrically superior, particularly for large-volume head/neck tumours.
Poster 2 Lattice Optimisation with Dual Degrees of Freedom Based on Real-Time Deformable Registration in SFRT
First author: Yi Peng et al. (China)
Purpose: Standard hexagonal close packing (HCP) lattice arrangements fail to conform to irregular tumour anatomy. This study develops a customised, anatomy-adapted lattice using geometric centre and rotation angle optimisation.
Results: Analysis of 115 HCP lattice cases. Dual degree of freedom (DoF) optimisation increased lattice density index to 6.56 ± 1.16 (vs. clinical 2.97-6.04); ADR improved to 2.43 ± 0.37. Regional variability in density indices highlighted.
Conclusion: Dual-DoF optimisation enables personalised dose sculpting and significantly improves dosimetric performance over fixed templates.
Poster 3 Column-Constrained VMAT Optimisation for SFRT
First author: Evan Porter et al. (USA)
Purpose: Proof-of-concept for column-constrained VMAT (ccVMAT), where each superior-inferior column of the lattice is treated with a dedicated arc, and MLCs are constrained to within 2.5 mm of the column surface.
Results: 3 sarcoma patients replanned. ccVMAT: steeper dose gradients, lower inter-target doses, gradient index 14.10 vs. 25.51 (IMRT) and 23.67 (VMAT). Longer delivery time (582 vs. 478 sec for VMAT).
Conclusion: ccVMAT improves conformality and intra-target heterogeneity at the cost of longer delivery times. Warrants further investigation.
Poster 4 Same-Day Simulation-Free Adaptive RT Using Varian Ethos
First author: Dennis Stanley et al. (USA)
Purpose: Evaluate the feasibility of same-day, simulation-free spatially fractionated adaptive radiotherapy (SF²-ART) using Ethos automated segmentation and cone beam CT (CBCT)-based adaptation.
Results: 10 patients (5 thoracic, 5 extremity) replanned in silico. All plans met dosimetric objectives; organs-at-risk (OAR) constraints satisfied. 100% passed Mobius3D QA (3%/2 mm). Median workflow: 166 min (consultation to delivery).
Conclusion: SF²-ART workflow is feasible and could reduce time-to-treatment from >1 week to <4 hours. High value for urgent/symptomatic patients.
Poster 5 Early Clinical Outcomes of Lattice SBRT for Bulky Advanced Tumours
First author: Natalie Wong et al. (Hong Kong)
Purpose: Describe outcomes of Lattice SBRT (5 fx, 20 Gy + simultan integrated boost (SIB) to 66.7 Gy) in 11 patients with bulky advanced malignancies (>6 cm).
Results: Objective response rate (ORR) 90.9% (1 complete remission (CR), 8 partial remission (PR)). 6-month local control (LC) 58.3%, progression-free survival (PFS) 31.2%, overall survival (OS) 63.6%. Median time to first response: 54 days. 1 patient proceeded to curative resection. Grade ≥3 toxicity in 27.3% (all manageable); no treatment-related deaths.
Conclusion: Lattice SBRT demonstrates rapid, promising tumour response with a favourable safety profile in advanced, refractory patients. Multi-centre prospective validation is warranted.
Poster 6: Can Target Partitioning Reduce Valley-to-Peak Dose for SFRT Lattice-VMAT?
First author: Agnes Angerud et al. (RaySearch)
Purpose: Investigate whether target partitioning can lower valley doses compared to standard VMAT in a face-centred-cubic lattice pattern (1400 cc abdominal clinical target volume (CTV)).
Results: Target partitioning reduced valley dose in coronal/sagittal planes; VMAT without partitioning gave lower transversal valleys. Neither approach achieved a <40% prescription dose in transversal valleys with limited couch kicks.
Conclusion: Target partitioning and VMAT are complementary; the optimal strategy is geometry-dependent. Transversal valley reduction remains challenging.
Poster 7 Static MLC-Based Patterns for SFRT-GRID
First author: Cozzi Luca (Italy)
Purpose: Propose and evaluate GRID patterns using standard MLC on clinical linear accelerators (LINACs), varying slit aperture (5–15 mm) and centre-to-centre distance (10–40 mm).
Results: For 5/10 mm slit/distance: Volume (V)(>90%)=20%, V(<30%)=0%. For 15/30 mm: V(>90%)=8%, V(<30%)=15%. Larger distances increase V(<30%), the hypothesised immune-stimulating low-dose volume. Spots vs. rods showed minimal dosimetric differences.
Conclusion: MLC-based GRID plans are dosimetrically feasible on standard LINACs. Optimal aperture/distance selection should account for target biology.
Poster 8 Combining ultra-high-dose rate radiotherapy and minibeam radiotherapy opens new rays of hope for enhancing anti-tumour and mitigating skin toxicity
First author: Shun Lu (China)
Purpose: Evaluate the biological effects of combining FLASH-RT (400 Gy/s) with MBRT in murine pancreatic cancer models.
Results: PVDR ≈ 3.5 (12 Gy peak / 3.5 Gy valley), EUD ≈ 5.4 Gy. On day 7, F-MBRT and MBRT tumour volumes were significantly lower than CONV-RT and FLASH-RT (p<0.01). At high dose (20 Gy), F-MBRT reduced skin collagen volume fraction significantly vs. FLASH-RT or MBRT alone (p<0.05). No significant femoral DNA damage differences between F-MBRT, FLASH-RT, and MBRT.
Conclusion: F-MBRT demonstrates synergistic anti-tumour efficacy and protective skin effects, representing a promising future radiotherapy modality.
Poster 9 Impact of centre-to-centre distance and slit width on robust target coverage and PVDR for proton minibeam radiation therapy using RayStation
First author: Anna Prins (The Netherlands)
Purpose: Investigate trade-offs between PVDR and robust target coverage in single-beam proton minibeam radiotherapy (pMBRT) across varied multi-slit collimator (MSC) parameters and beam geometries.
Results: Trade-off observed: high entrance PVDR reduces coverage; sufficient coverage reduces PVDR. Intermediate depths (6-15 cm) offer the best balance. Oblique angles and large depths reduce entrance PVDR (<2.7). Tumour control probability (TCP) comparable to open beam when target PVDR <1.2.
Conclusion: Robust single-beam pMBRT planning is feasible in RayStation but geometry-dependent. Findings guide future robust pMBRT planning investigations.
Poster 10 Microbeam Radiotherapy on the road to clinical application - what to treat first?
First author: Kim Melanie Kraus (Germany)
Purpose: Identify clinically relevant and dosimetrically feasible first-in-human MRT targets using a compact x-ray source (300 kVp, 50 µm beamlets, 400 µm centre-to-centre (CTC)). Nine patient cases were evaluated.
Results: Best target coverage and OAR sparing achieved by two gluteal tumour cases. D95% coverage 95.4–105.8%. PVDR in the isocenter 9.3–21.1. Superficial targets with limited tissue inhomogeneity are best suited dosimetrically.
Conclusion: MRT can deliver safe, effective dose distributions to relevant superficial targets. Gluteal, nuchal and inguinal tumours identified as strong candidates for a first-in-human phase 1 safety trial.
Poster 11 Evaluation of novel robustness strategies in Lattice Proton Arc Therapy employing translationally invariant dose patterns and shoot-through layers
First author: Erik Engwall (Sweden)
Purpose: Propose a new robust optimisation approach that preserves lattice peaks and valleys under positioning uncertainties by allowing the lattice pattern to translate within the GTV, rather than blurring the dose pattern.
Methods: Applied to 2 abdominal patients previously treated with VMAT lattice. Plans optimised on IBA ProteusPlus: proton arc (PAT), shoot-through enhanced arc (PAT+ST), shoot-through-only (ST-PAT), and VMAT. 21 robustness scenarios (5 mm setup, ±3% range).
Key Results: New robust optimisation-maintained vertex doses under uncertainties while reducing dose to patient and lattice volumes vs. standard robustness and VMAT. Shoot-through layers sharpened the lattice pattern at the expense of slight increases in external, left kidney, and bowel doses.
Conclusion: New robust optimisation preserves robustness while improving lattice characteristics. Shoot-through enhanced proton arc plans could further enhance results.
Poster 12 VMAT-Based Lattice Radiotherapy for Large Hepatocellular Carcinoma: Feasibility, Safety, and Early Immune-Compatible Response
First author: Yu-Wei Lin (Taiwan)
Purpose: Evaluate the feasibility, early response, and safety of VMAT-based lattice radiotherapy (LRT) for large HCC (>400 cm³) with limited hepatic reserve.
Methods: 7 patients (8 LRT courses), Oct 2024-Aug 2025. Plans: 8-24 high-dose spheres (18-20 Gy, single fraction) + peripheral doses (20-52.5 Gy, 5-15 fx). 5 patients received concurrent atezolizumab/bevacizumab.
Key Results: Median follow-up 6 months. No acute toxicity above Grade 2; no radiation-induced liver disease. At 3 months, the median tumour volume reduction 55%. 2 patients converted from partial to complete response. Rapid early regression in 2 cases within the first 1-3 fractions.
Conclusion: VMAT-based LRT is feasible and OAR sparing for large HCC with potential immune-mediated synergy when combined with systemic therapy.
Poster 13 Robotic Gyroscopic Lattice Radiotherapy for Recurrent or Progressive High-Grade Gliomas: Largest Secondary Re-Irradiation Cohort to Date
First author: Sepideh Mohammadipour (Turkey)
Purpose: Assess safety, feasibility, and outcomes of LRT using ZAP-X gyroscopic radiosurgery platform in patients with recurrent/progressive HGG after at least 2 prior RT courses (RT1 and RT2).
Methods: 11 patients, Dec 2024-Aug 2025. Single-fraction LRT, custom Python software for 20 Gy vertex planning. GTV included all fluid-attenuated inversion recovery (FLAIR) changes on MRI.
Key Results: Median follow-up 4.5 months. No serious adverse events; no symptomatic radiation necrosis. Median OS 5.9 months (95% CI: 3-9), PFS 4.7 months (95% confidence interval (CI): 3-7). Better PFS trend for RT2-LRT interval ≥12 months and GTV ≤200 cm³. Response to RT2 significantly influenced OS/PFS. 1 pembrolizumab-treated patient achieved a complete response maintained for 6.5 months.
Conclusion: LRT is a feasible option in recurrent large HGG with short but notable survival benefit. Combination with immunotherapy warrants further investigation.
Poster 14 Script-Based Automatization for Lattice Dosimetry Planning in RayStation for Tomotherapy
First author: Rafael Chona Perea (Colombia)
Purpose: Automate sphere creation, placement, and planning for lattice treatments on a tomotherapy machine using RayStation scripting, without sacrificing customisation.
Methods: Tested on 10 patients (breast, head/neck, cervix). Automated region of interest (ROI) creation, beam setup, and optimisation from planning target volume (PTV) contour to viable dosimetric plan.
Key Results: Planning time reduced from 1–2 days to approximately 1 hour for a plan with 65 spheres. Shorter times for smaller PTVs. Complete workflow: sphere placement, auxiliary structure creation, beam configuration, optimisation objectives.
Conclusion: Automated lattice planning on tomotherapy is feasible and clinically relevant, as lattice patients are often in urgent need of radiation treatment.
Poster 15 Encouraging clinical outcomes from the first 20 patients treated with a Helical Lattice-VMAT approach, enhancing low-valley dose reduction
First author: Santiago Velázquez-Miranda (Spain)
Purpose: Evaluate clinical outcomes and dosimetric indices for HelixRad, a VMAT-based helical vertex arrangement using the negative margin technique to reduce peripheral dose and deepen valleys.
Methods: 20 patients with bulky unresectable tumours (>5 cm, ECOG ≤2). Single-fraction HelixRad (Dmin,vertex=12 Gy; Dmax, vertex≈20 Gy; Dvalley<3 Gy). 6-month follow-up. Cork3 and Cork5 indices proposed as spatial heterogeneity biomarkers.
Key Results: 30% abscopal response rate (regression of non-irradiated lesions). 55% showed >30% tumour reduction at 6 months with improved pain and global health. Most plans: valley <3 Gy, V5[CorkGTV]<10%, V3[CorkGTV]<35%. Delivery time <7 min. Cork3 positively correlated with systemic response (Spearman ρ=0.32).
Conclusion: HelixRad achieved efficient clinical workflow and preliminary evidence that the cork3 index may serve as a radiobiological biomarker for systemic response.
Poster 16 LATTICE Radiotherapy for Advanced Sarcomas: Feasibility, Efficacy and Safety in 21 Patients with No Therapeutic Alternative
First author: Marie-Pierre Sunyach (France)
Purpose: Evaluate the feasibility, efficacy, and safety of LRT in 21 patients with advanced sarcomas in therapeutic impasse (2022–2025).
Methods: Histologies included undifferentiated sarcoma, liposarcoma, chordoma, chondrosarcoma, malignant peripheral nerve sheath tumour (MPNST), and others. Sites: abdominal (15), intrathoracic (2), limb root (3), foot (1), abdominal wall (1). MIM Maestro + Monaco TPS, 6MV flattening filter free (FFF) VMAT on Versa HD. Prescribed 12 Gy at 80% isodose to peaks; peripheral 2-7 Gy.
Key Results: LRT feasible in all cases, including re-irradiation. Tumour response: 4 with 70-90% reduction, 4 with 20–50%, 6 with 0-20%, 1 progressive disease, 6 non-evaluable. No toxicity >Grade 3. Partial response in 9 patients.
Conclusion: LRT is a feasible, safe, and potentially effective option for advanced sarcomas with no therapeutic alternative. Fluorodeoxyglucose (FDG)-positron emission tomography (PET) integration for sphere positioning under further investigation.
Poster 17 VMAT Lattice Radiotherapy in Bulky Head-and-Neck Tumours: Dosimetric Analysis and Clinical Outcomes
First author: Diego Rodolfo Fernandez (Argentina)
Purpose: Evaluate clinical outcomes, local control, OS, toxicity, and dosimetry of VMAT lattice RT in 40 patients with bulky head-and-neck tumours (2020–2025).
Methods: Eclipse TPS, 6 MV photon VMAT. Analysed VTV dose, GTV prescribed dose, number of vertices, fractions, volumetric changes, toxicity, and survival.
Key Results: Mean VTV: 8 (range 2–30). Mean VolumeVTV/VolumeGTV: 1.4%. Mean GTV reduction: 27.2%. 2 complete responses (laryngeal carcinoma; indeterminate origin). Median OS: 6.3 months. Longest OS: laryngeal carcinoma (31.2 months). Grade ≥3 toxicity uncommon (GI n=0, dermal n=7, mucosal n=11).
Conclusion: VMAT lattice is feasible, safe, and well-tolerated in bulky head-and-neck tumours, achieving meaningful volumetric responses with low early progression.
Poster 18 Applications in Clinical Practice of Lattice Radiation Therapy: Results and Future Possibilities
First author: Davide Di Gennaro (Italy)
Purpose: Report clinical results and explore possibilities of LRT for bulky cancers in a single-centre cohort of 34 patients (35 treatments, Dec 2023–Jun 2025).
Methods: Monaco TPS (MC), Elekta Versa HD, VMAT. Cylindrical vertices (Ø 1–1.2 cm, separation 1.5–2.0 cm). Mean vertices (CTVert)/CTVT ratio: mean 2.8%. Dose to vertices: 5 Gy/1 fx to 50 Gy/4 fx. Dose to CTV: 8 Gy/1 fx to 70 Gy/35 fx. Delivery modes: simultaneous integrated boost, Strip-Therapy, twice-daily.
Key Results: 31 patients completed treatment without related toxicities. 4 patients died from chemo/immunotherapy-related toxicity. Relief of symptoms (dyspnoea, pain, functional impotence) was observed at 1 month in all. 22/31 patients alive at 18 months; 4 alive at 36 months.
Conclusion: LRT is safe and effective for bulky cancers, delivering ablative intratumoural doses while limiting OAR exposure. Growing experience aims to transition palliative to curative intent.
Poster 19 Early Clinical Experience of Lattice Radiotherapy in Bulky, Unresectable Soft Tissue Tumours: A Single-Centre Cohort from Oman
First author: Khadiga Mohammed (Oman)
Purpose: Present the first regional Middle East experience of LRT for large, unresectable, or metastatic soft tissue tumours (STT) treated between 2023 and 2025.
Methods: 5 female patients (median age 41 years). Histologies: desmoid fibromatosis, undifferentiated high-grade sarcoma, MPNST, synovial sarcoma, spindle cell sarcoma. VMAT-based LRT, 1-3 fractions, 12-18 Gy total. Median GTV 1,758 cc (range: 180-2,340 cc). Median 23 vertices, Ø 1 cm, centre-to-centre spacing 2.6 cm.
Key Results: All patients completed treatment without interruption. Grade 1-2 dermatitis or transient pain only; no Grade ≥3 toxicity. Symptomatic relief in all evaluable patients within 1-3 weeks. Partial response or stable disease in 4 assessable patients; median tumour volume reduction 28%. All showed intratumoural necrosis. 1 patient underwent successful surgical resection after LRT.
Conclusion: First LRT experience from the Middle East demonstrates feasibility, safety, and efficacy in bulky sarcomas. Prospective trials needed to define optimal dosimetry and long-term outcomes.
Poster 20 Partially Ablative Body Radiotherapy (PABR) for Large Unresectable Tumours: A Single Institution Experience
First author: Jorge Obeso-Herrera (Spain)
Methods: 9 patients. GTV integrated boost of 50 Gy prescribed to the tumour core (GTV contracted by 1–1.5 cm); 20 Gy prescribed to the peripheral PTV (GTV + 1 cm isometric expansion). Delivered in 5 fractions using VMAT with IGRT before each session. Pain assessed by visual analogue scale (VAS); volumetric response by CT at 3–6 months.
Key Results: Median age 63 years (range: 5-94). Histologies: 67% sarcomas, 22% squamous cell carcinoma, 11% medulloblastoma. Sites: 33% head/neck, 33% abdomen, 22% limbs, 11% thorax. 55.6% ECOG 2; 77.8% stage IV; 66.7% high-grade. Median tumour volume 921 cc (range 94–3,984 cc); all long diameters >7 cm (max 31.4 cm). 100% of patients had pain improvement (VAS reduction from 8 to 2). Radiologic partial response in 78% (n=7), stable disease in 11% (n=1), radiologic progression in 11% (n=1). However, 82.3% of post-treatment tumour mass corresponded to necrotic tissue, reclassified as pseudo-progression.
Conclusion: PABR is an accessible and safe treatment tool with excellent symptomatic and volumetric responses in patients with advanced unresectable tumours.
Conclusions
ESTRO 2026 reinforced that SFRT is transitioning from a niche preclinical curiosity to a clinically meaningful modality with growing evidence, infrastructure, and community. The key messages emerging from Stockholm are:
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Immunological mechanisms of MBRT are becoming well characterised - the ICAM1/LFA1 axis, vascular normalisation, and interplay with immunotherapy are increasingly well-defined targets for radio-immunotherapy combinations.
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Preclinical data continue to accumulate across tumour types (TNBC, pancreatic, CNS), supporting expansion of SFRT indications and doses.
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Treatment planning innovations - GPU-accelerated MC for MRT, adaptive SF²-ART, ccVMAT, hybrid CyberKnife/VMAT, HelixRad, automated tomotherapy scripting - are closing the gap between clinical promise and practical implementation.
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First-in-human data for ultra-high-dose PTI combined with immunotherapy demonstrate feasibility, safety, and striking tumour responses - including abscopal effects - in patients with no remaining treatment options.
Dora Correia
Radiation Oncology Centre Mittelland, Kantonsspital Aarau, Switzerland
Member of the SFRT ESTRO Focus Group
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dora.correia@ksa.ch
https://www.linkedin.com/in/doracorreia/
X: @The_PT_Explorer
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Verdiana Trappetti
Institute of Anatomy, University of Bern, Switzerland
verdiana.trappetti@unibe.ch
www.linkedin.com/in/verdiana-trappetti-92aa13128