ESTRO 2025 - Abstract Book

S527

Clinical - Breast

ESTRO 2025

association reported in other studies, ongoing efforts to establish an association are unlikely to yield clinically meaningful insights.

Keywords: cardiac, biomarker, radiotherapy

References: 1. Chufal K, Ahmad I, Prakash A, et al. Cardiac markers in left-sided breast cancer patients receiving adjuvant radiotherapy: a prospective study. Cardio-Oncol 2024; 10:21.

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Digital Poster A Radiotherapy Fixed Field IMRT Solution Limiting Low Dose Spillage for Complex Breast Patients on a Varian Halcyon Sandra Dymond 1 , Katie Long 1 , Junman To 1 , Caroline Balcombe 1 , Liz Adams 1 , Dualta McQuaid 1 , Felicity Paterson 2 , May Teoh 2 1 Radiotherapy Physics, Royal Surrey County Hospital, Guildford, United Kingdom. 2 Clinical Oncologist, Royal Surrey County Hospital, Guildford, United Kingdom Purpose/Objective: The Varian Halcyon is a 6MV flattening-filter-free (6FFF) linac using a dual-layer multi leaf collimator (MLC) system rather than jaws to define field borders. Standard breast and nodal treatments consist of tangents to the breast with matched fields to treat nodes thus minimising dose to heart and lung and low dose spillage to healthy tissue. 6FFF limits target coverage using this technique, especially for patients with a high BMI or breast post-border separation over 22cm [1] Studies have suggested that arc and multiple field radiotherapy, which would help improve coverage, could potentially increase the excess absolute risk (EAR) of solid secondary cancers as larger volumes may be irradiated to low doses [2-3]. An alternative technique balancing coverage with minimal low dose spillage to healthy tissue was therefore developed. Material/Methods: An IMRT “butterfly” technique was developed using 2-6 static IMRT fields based around tangential angles (1-3 medial and 1-3 lateral, spaced 5 degrees apart) for the breast treatment. Further anterior and posterior fields encompassing axillary lymph nodes were included for IMRT optimisation. Ring structures minimised spillage outside of PTVs Nine patients were planned retrospectively for a prescribed dose of 40Gy in 15 fractions, comparing three techniques with dose statistics recorded (see Fig 1 Results); • Field-in-field using a standard matched field technique on a Varian TrueBeam where higher beam energies could be used to improve target coverage (FiF-TB) • IMRT using the 6FFF butterfly technique on a Halcyon (IMRT-HAL) • VMAT using two 6FFF partial (240 degree) Arcs on a Halcyon (VMAT-HAL) Results: Both IMRT and VMAT solutions gave improved coverage compared with FiF. Contralateral OAR doses were comparable between FiF and IMRT, with VMAT doses being considerably higher, particularly for the contralateral lung (See Fig1). Normal tissue dose was generally slightly higher with IMRT than FiF but substantially lower than VMAT (See Fig 2).