ESTRO 2025 - Abstract Book

S1529

Clinical – Mixed sites & palliation

ESTRO 2025

References: 1. Papalazarou C, Klop GJ, Milder MTW, Marijnissen JPA, Gupta V, Heijmen BJM, Nuyttens JJME, Hoogeman MS. CyberKnife with integrated CT-on-rails: System description and first clinical application for pancreas SBRT. Med Phys. 2017 Sep;44(9):4816-4827.

2742

Digital Poster SBRT- PATHY for Unresectable Tumors: Our Center’s Experience

Maria Borrás Calbo 1 , Rodolfo Chicas-Sett 1 , Emilio Murcia Nadal 1 , Erika Paola Romero Benavides 1 , Yolanda Real Kotbani 2 , Beatriz Geanina Cristea 1 , Maria José Pérez Calatayud 1 , Francisco Javier Celada Álvarez 1 , Marian Estornell Gualde 1 , Dolores Farga Albiol 1 , Miguel Ángel Berenguer Francés 1 , Julien Alcaide de Wandeleer 3 , Vicente Carmona Meseguer 3 , Antonio Jose Conde Moreno 1 1 Department of Radiation Oncology, Hospital Universitario y Politécnico La Fe, Valencia, Spain. 2 Department of Radiation Oncology, Hospital Universitario y Politécnico La Fe, Valenica, Spain. 3 Department of Medical Phiysics, Hospital Universitario y Politécnico La Fe, Valencia, Spain Purpose/Objective: Bulky tumors are aggressive malignancies frequently linked to poor prognosis and limited treatment options, often relegating patients to palliative or supportive care. SBRT-PATHY, a novel partial irradiation technique, reduces tumor volume while preserving the peritumoral immune microenvironment (PIM), enhancing synergy with systemic therapies like immunotherapy. This study aims to retrospectively assess the clinical outcomes and therapeutic potential of SBRT-PATHY in the management of unresectable cancers at our institution. Material/Methods: From March 2023 to November 2024, 15 lesions in 13 patients with unresectable advanced solid tumors were treated with SBRT-PATHY. Primary tumor sites included lungs (9), head and neck (2), soft tissue (1), and cervical cancer (1). All but one patient had prior systemic therapy. Treatment indications were mostly for symptomatic palliation, except in four cases: two for synergistic immunologic effects and two for cytoreduction. CT and PET-CT (when available) guided the delineation of the bystander tumor volume (BTV) and identification of necrotic areas. Two tailored treatment plans were created for each patient: one covering the entire PIM and another using "immune islands" within the PIM to meet strict dose constraints. Results: Of the 15 lesions treated, 67% were pulmonary (n=10) and 33% hepatic (n=5), with a mean tumor volume of 430.95 cc (range 44.5-1379.5 cc). BTV represented an average of 25% of GTV. Most treatments (93%, n=14) were delivered in a single fraction, except one case requiring three fractions. "Immune islands” were implemented in 10 cases to preserve the PIM. 77% (n=10) of patients received systemic therapy concurrently with radiotherapy. Systemic therapy was interrupted in two patients, one on a therapeutic break due to toxicity and the other voluntarily discontinuing treatment, neither related to radiotherapy. Local control, assessed by RECIST criteria, showed complete response in 38% of patients (n=5), local progression in 15% (n=2), and unevaluable results in the rest due to lack of imaging or patient death. Among symptomatic patients (n=9), 89% (n=8) reported symptom relief. No significant toxicity was observed. Conclusion: SBRT-PATHY achieved significant tumor volume reductions without added toxicity, underscoring its potential as a safe and immune-supportive treatment strategy. Prospective studies aim to optimize patient selection and identify predictive biomarkers to maximize its benefits.