ESTRO 2025 - Abstract Book

S1524

Clinical – Mixed sites & palliation

ESTRO 2025

In Stereotactic Body Radiotherapy (SBRT), abdominal compression devices and respiratory/surface tracking systems are commonly used to manage respiratory-induced organ motion. The high cost, bulky design, and low patient tolerance of these devices limit access and prolong treatment times, prompting the use of non-custom synthetic corsets as a practical alternative. We aimed to evaluate the effectiveness and reliability of corsets in SBRT targeting lower thoracic and upper gastrointestinal tumors. Material/Methods: A total of 46 patients included in the study underwent two separate slow-CT scans with 1 mm slice thickness, with and without a corset. In scans with corset, a lumbosacral corset with a front-to-back tensile band used and the maximum compression that the patients could tolerate was provided. The diaphragm motion of patients treated with the abdominal compression with shallow breathing (ACSB) technique was evaluated by measuring diaphragm amplitude(cm), Δamplitude(cm), liver and spleen artifact volumes(cc), and their changes(Δvolume)(cc). Results: The median age of the patients was 67 years (45 – 82), with 17 females and 29 males. The mean BMI (Body Mass Index) was 26.2±5.0 kg/m². The corset decreased the diaphragm amplitude from a median of 1.13 cm (0.20 – 3.01) to 0.55 cm (0.17 – 1.93)(p<0.001). Patients with an initial diaphragm amplitude greater than 1 cm had a median reduction of -0.84 cm, whereas those with an initial amplitude less than 0.5 cm showed a median reduction of -0.13 cm (p=0.000)(Figure 1). In non- corset CT scans, 39.1% of patients had a diaphragm amplitude ≤1 cm, increasing to 82.6% with a corset. Both univariate and multivariate logistic regression analyses found no significant effect of gender, age, or BMI on Δamplitude and Δvolume changes with the corset (p>0.05). At 6 months post -SBRT, 73.9% of patients showed complete, 17.4% partial response, 4.3% stable disease, and 4.3% progression. Median follow-up was 9 months (3 – 24). Median time to local progression was 9.5 months (2.4 – 27) and systemic progression 6.2 months (1.4 – 27). Local progression occurred in five patients, all of them also had systemic progression. Conclusion: In the immunotherapy era and the frequent treatment of oligometastatic disease with curative intent, the need for SBRT is increasing. The lack of motion management devices does not hinder the application of SBRT to lower thoracic and upper gastrointestinal tumors. The ACSB technique with a non-custom corset effectively managed motion in patients with diaphragm amplitudes over 1 cm and proved reliable for clinical applications.

Keywords: SBRT, Diaphragm Motion Management, Corset

2615

Digital Poster Hyperthermia and Radiotherapy Clinical Trials at Catalan Institute of Oncology: Initial Results Marina Arangüena Peñacoba 1 , Olalla Santacruz González 1 , Josep Jové Teixidó 2 , María Aránzaru Eraso Urien 3 , Cristina Gutiérrz Miguélez 1 , Evelyn Martínez Pérez 1 , Hector Pérez Montero 1 , Javier González Viguera 1 , Leyre Asiaín Azcárate 1 , Pablo Araguas Mora 1 , Montserrat Ventura Bujalance 1 , Joaquina Valera Muñoz 1 , María Cristina Siria López 1 , Pilar Fernández López 1 , Salvador Villà Freixa 2 , Alicia Lozano Borbalas 1 , Dina Najjari Jamal 1 , Milica Stefanovic 1 , Makarena Soledad Villalobos Monardes 1 1 Radiation Oncology, Catalan Institute of Oncology, Barcelona, Spain. 2 Radiation Oncology, Catalan Institute of Oncology, Badalona, Spain. 3 Radiation Oncology, Catalan Institute of Oncology, Girona, Spain Purpose/Objective: This prospective study evaluates the safety of combining hyperthermia (HT) with radiotherapy (RT) in two ongoing phase II clinical trials conducted at the three centers of the Catalan Institute of Oncology (ICO). The primary objective is to assess acute and late toxicity (CTCAE v5.0), while secondary endpoints include local control and