ESTRO 2025 - Abstract Book

S560

Clinical - Breast

ESTRO 2025

radiotherapy imaging modality (CT scan vs. chest X-ray, p=0.002). Clinical factors and radiotherapy parameters did not significantly influence RILD occurrence.

Conclusion: Radiographic findings of RILD in breast cancer patients treated with TomoTherapy showed an incidence consistent with the literature, with no significant difference in RILD occurrence between TomoDirect and TomoHelical modes. The use of hypofractionation in TomoHelical mode may obscure differences in lung dose parameters. Additional research is needed to comprehend the nuanced relationships between treatment modes, lung dose parameters, and clinical factors, guiding clinical decisions for breast cancer patients undergoing radiation therapy.

Keywords: Radiation-Induced Lung Disease, Tomotherapy

References: Giuranno L, et al. Radiation-induced lung injury (RILI). Front Oncol . 2019;9:877. Han S, et al. Clinical and dosimetric factors influencing radiation-induced lung injury in lung cancer. J Cancer . 2015;6(11):1172–8. Arroyo-Hernández M, et al. Radiation-induced lung injury: current evidence. BMC Pulm Med . 2021;21:9. Vogelius IR, et al. Meta-analysis of clinical risk factors for radiation-induced pneumonitis. Acta Oncol . 2012;51(8):975– 83. Madani I, et al. Predicting risk of radiation-induced lung injury. J Thorac Oncol . 2007;2(9):864–74. Nobnop W, et al. Dosimetric comparison of TomoDirect, Helical TomoTherapy, and VMAT for postmastectomy treatment. J Appl Clin Med Phys . 2020;21(9):155–62.

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Digital Poster Safety of trastuzumab emtansine and concomitant radiation therapy in patients with metastatic HER2 positive breast cancer Marianna Valzano 1 , Kathrine Kargaard Schulz 2 , Mette Lundsteen 2 , Luca Visani 1 , Carlotta Becherini 1 , Viola Salvestrini1 1 , Ilaria Bonaparte1 1 , Maja Bendtsen Sharma2 2 , Lorenzo Livi 1 , Icro Meattini 1 , Birgitte Offersen 2 1 Radiation Oncology,, Azienda Ospedaliero Universitaria Careggi, University of Florence, Florence, Italy. 2 Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark Purpose/Objective: In metastatic breast cancer (mBC), radiation therapy (RT) plays a critical role in disease management, either with palliative or ablative intent. Limited data exist on the risk of toxicity from the concurrent use of RT and systemic therapies. Preliminary findings have raised concerns about potential increased toxicity, particularly for intracranial treatments. This study aims to assess the incidence of acute and late adverse events in patients treated with concurrent trastuzumab emtansine (T-DM1) and RT, and to evaluate correlations with dosimetric data. Material/Methods: Patients with HER2-positive mBC who received T-DM1 and concomitant RT between January 2019 and May 2024 at two European University Hospitals, in Florence (Italy) and Aarhus (Denmark), were included. Concomitant RT was defined as RT delivered within 20 days of T-DM1 administration. Patient, tumour, therapy, and dosimetric details were extracted from medical registries. Acute and late toxicities were recorded and graded according to the Common Terminology Criteria for Adverse Events v5.0. Results: Thirty-six patients, accounting for 77 treatments, were included, with a median follow-up of 23 months (range 1–83). The median age was 54 years (range 31–81), and T-DM1 was administered as second-line therapy in the majority