ESTRO 2025 - Abstract Book

S4015

Radiobiology - Tumour radiobiology

ESTRO 2025

Conclusion: Positive correlation of ERCC5 gene upregulation with advanced stage indicates its role in Cervical cancer progression. Also, significantly higher mRNA and protein expression suggests role as a potential diagnostic marker. Upregulation may be inferiorly associated with OS.

Keywords: ERCC5 gene, expression, survival

3835

Digital Poster Exploring Dose-Escalated ultra-hypofractionation in Breast Cancer Radiotherapy: an In-Silico, biological driven study Denis Panizza 1,2 , Valeria Faccenda 1 , Riccardo Ray Colciago 2 , Marco Calvaruso 3 , Gaia Pucci 3 , Francesco Paolo Cammarata 3 , Valentina Bravatà 3 , Giorgio Russo 3 , Giusi Irma Forte 3 , Luigi Minafra 3 , Elena De Ponti 1,2 , Stefano Arcangeli 2,4 1 Medical Physics, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. 2 School of Medicine and Surgery, University of Milan Bicocca, Milan, Italy. 3 Institute of Bioimaging and Complex Biological Systems (IBSBC), National Research Council (CNR), Cefalù, Italy. 4 Radiation Oncology, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy Purpose/Objective: The aim of this study is to evaluate the feasibility of delivering escalated dose regimens for breast cancers requiring doses beyond ultra-hypofractionated limits. Specifically, it investigates the dose per fraction and total dose for triple-negative breast cancer (TNBC) cell lines required to achieve a local disease-free survival rate (LSR) close to 100%. Material/Methods: TNBC cell lines were utilized as in vitro models for radiobiological characterization, and three treatment schemes were experimentally determined using the 100% LSR objective: 9.1 Gy x 5 fractions (α/β=16.51); 8 Gy x 5 fractions (α/β=5.95); and 9.9 Gy x 5 fractions (α/β=22.93). Fifteen treatment plans of breast cancer patients treated in deep inspiration breath hold were replanned using the highest dose (9.9 Gy x 5) to simulate the worst scenario. The plans were optimized to cover the whole breast clinical target volume (CTV), adding a 7 mm margin for the planning target volume (PTV), using a 2-arc VMAT technique with 6FFF beams. Dose constraints for the OARs were used according to the Fast Forward protocol, aiming to achieve an optimal balance between target coverage and OAR dose limits. Results: The majority of the 9.9 Gy x 5 plans failed to achieve the dosimetric objectives while also not achieving full CTV coverage. The ipsilateral lung volume receiving 8 Gy ranged from 17% to 27%, exceeding the 15% limit set by the Fast Forward protocol. Similarly, the heart volume receiving 1.5 Gy ranged from 29% to 40%, compared to the protocol threshold of 30%. However, the heart volume receiving 7 Gy always remained below the 5% threshold. The target coverage for the CTV ranged from 75% to 90% of the prescribed dose, while coverage for the PTV ranged from 70% to 82% of 95% of the prescribed dose. Maximum doses (105% and 107%) were always within the protocol thresholds. The mean (standard deviation) target dose was 49.3 Gy (0.3), slightly below the prescribed dose. The mean dose to the contralateral breast ranged from 1.9 Gy to 3.2 Gy. Conclusion: The study reported suboptimal target coverage, accompanied by unmet dose constraints for ipsilateral lung and heart. Additionally, the risk of radiation-induced fibrosis increased with higher maximum doses to the whole breast. These findings highlight the need for an alternative dose-escalation approach to achieve the same LSR. A potential strategy will involve delivering a pre-surgical boost to the lesion, followed by an ultra-hypofractionated treatment in 5 fractions. Keywords: breast cancer, biological-driven RT