S877
Clinical - Mixed sites & palliation
ESTRO 2026
Grade ≥ 2 toxicity occurred in 1/7 patients (14%) for both GI and GU events. Gastrointestinal acute and late toxicity was grade 1–2 and grade 0–1 respectively. A grade 3 urinary retention was observed in a ISUP 5 prostate cancer treated with short-course RT. Conclusion: Combined radiotherapy for synchronous prostate and rectal cancer is feasible and well tolerated. The short- course regimen appears advantageous when early surgery is required, although it is necessary to consider late genitourinary toxicity. Multicentric collaboration is needed to establish optimized protocols and strategies in this rare scenario. References: Lavan NA et al. Br J Radiol. 2016;89:20150292.Tey YQ et al. Medicine (Baltimore). 2020;99:e20336.Edfelt E et al. Acta Oncol. 2025;64:374–379.Nassar A et al. Int J Colorectal Dis. 2025;40:195–206.Wu V et al. J Clin Oncol. 2022;40(16 suppl):e15591.Sidiqi BU et al. Int J Radiat Oncol Biol Phys. 2023;117(2 Suppl):e339.U.S. Dept. Health & Human Services, NCI. CTCAE v5.0. Bethesda (MD): NIH; 2017. Keywords: synchronic, prostate, rectum Spatially Fractionated Radiotherapy (SFRT) for Bulky Tumors: A Systematic Review of Clinical Outcomes and Dosimetric Variability Rossella DI FRANCO 1 , Rocco Mottareale 1 , Donato Pezzulla 2 , Simona Mercogliano 1 , Maria Antonietta di Franco 1 , Valentina Borzillo 1 , Esmeralda Scipilliti 1 , Giustino Silvestro 1 , Giampaolo De Palma 1 , Marcello Serra 1 , Gianluca Ametrano 1 , Francesca Buonanno 1 , Cecilia Arrichiello 1 , Valentina d'Alesio 1 , Savino Cilla 2 , Arturo Cuomo 3 , Ernesta Cavalcanti 4 , Ernesto Maranzano 5 , Fabio Arcidiacono 6 , Costanza Donati 7 , Francesco Cellini 8 , Vincenzo Ravo 1 1 Radiation Oncology, Istituto Nazionale Tumori - IRCCS Fondazione "G. Pascale", Napoli, Italy. 2 Radiation Oncology Unit, Responsible Research Hospital, Campobasso, Italy. 3 Division of Anesthesia and Pain Medicine, Istituto Nazionale Tumori - IRCCS Fondazione "G. Pascale", Napoli, Italy. 4 Laboratory Medicine Unit, Istituto Nazionale Tumori - IRCCS Fondazione "G. Pascale", Napoli, Italy. 5 Radiation Oncology, Istituto Nazionale Tumori - IRCCS Fondazione "G. Pascale", Perugia, Italy. 6 SC Radioterapia Oncologica, Azienda Ospedaliera S. Poster Discussion 1899 Maria, Terni, Italy. 7 Radiation Oncology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy. 8 Dipartimento di Diagnostica per Immagini, Fondazione Policlinico Universitario “A. Gemelli” IRCCS,
UOC di Radioterapia Oncologica ed Ematologia, Roma, Italy
Purpose/Objective: Conventional radiotherapy (CRT) for bulky and radioresistant tumors is often constrained by normal tissue tolerance, limiting dose escalation and tumor control. Spatially Fractionated Radiation Therapy (SFRT), including GRID and Lattice Radiotherapy (LRT), overcomes these limitations by delivering highly heterogeneous intratumoral dose distributions. This approach is hypothesized to induce distinctive radiobiological effects, such as immune activation and vascular normalization. The aim of this systematic review was to assess the evolution, clinical efficacy, safety, and dosimetric characteristics of SFRT techniques. Material/Methods: A systematic literature review was performed using the MEDLINE database for studies published between January 2010 and June 2025. Search terms included “Spatially Fractionated,” “Lattice,” “GRID,” and “radiotherapy.” Eligible English-language studies encompassed case reports, case series, and prospective trials. Extracted data included patient demographics, tumor characteristics, treatment intent, clinical outcomes, toxicity, and dosimetric parameters, particularly the Valley-to-Peak Dose Ratio (VPDR). Results: Twenty-seven studies involving 363 patients and 468 lesions were analyzed. The most common tumor sites were the thorax (37.8%) and abdomen (16.7%), with sarcomas (34.4%) and non-small cell lung cancer (15.7%) representing the predominant histologies. Most treatments were performed with palliative intent (194 cases). Tumor regression was observed in approximately 80% of lesions, accompanied by consistent symptom improvement. Reported toxicities were generally mild (Grade 1–2), while severe adverse events (Grade ≥ 3) were rare, underscoring the safety of SFRT when properly planned. Significant variability was identified in VPDR definitions and values, ranging from 0.04 to 0.30 in highly heterogeneous dose distributions and 0.23–0.25 in moderately heterogeneous ones. Differences in tumor sites, lattice geometry, and calculation methods contributed to this heterogeneity, emphasizing the need for standardized reporting. The median VTV volume was 2.7 cc (range: 0.5–26.5 cc; mean 5.6 ± 5.4 cc), corresponding to a VTV-to-GTV ratio of 1.0% (mean 0.9 ± 0.7%). The median number of spherical vertices was 7 (range: 1– 18), with a mean vertex diameter of 1.2 ± 0.2 cm and a center-to-center spacing of 3.8 ± 1.1 cm. Dose prescriptions ranged from 8–20 Gy per fraction for VTVs and 3–6 Gy per fraction for valley regions.
Made with FlippingBook - Share PDF online