S325
Clinical - Breast
ESTRO 2026
Birgitte Offersen 8 , Sylvia O'Keeffe 5 , Francesca Holt 7 , Elizabeth M Connolly 5 , Frances K Duane 1,2 1 Radiation Oncology, St. Luke's Radiation Oncology Network, Dublin, Ireland. 2 Applied Radiation Therapy Trinity, Discipline of Radiation Therapy,, Trinity College Dublin, Ireland. 3 Erasmus MC Cancer Insititute, Univesity Medical Center, Department of Radiotherapy, Rotterdam, Netherlands. 4 Cancer Research @UCC, College of Medicine and Health, University College Cork, Cork, Ireland. 5 Trinity St. James's Cancer Institute, St James' Hospital, Trinity College Dublin, Ireland. 6 Beaumont Cancer Institute, RCSI, Dublin, Ireland. 7 Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom. 8 Department of Experimental Clinical Oncology, Department of Oncology, Aarhus, Denmark Purpose/Objective: Regional nodal irradiation (RNI) improves survival for patients with node positive breast cancer following axillary lymph node dissection (ALND). ALND remains indicated for high-risk cases, including those with clinically node positive disease, locally advanced disease or residual disease post systemic therapy. There is substantial inter-observer variation in contouring the residual axillary nodal basin following ALND during modern radiotherapy planning. This study aims to present a multidisciplinary guideline for defining this region on radiotherapy CT-planning scans. Material/Methods: A multidisciplinary taskforce including radiation oncologists, radiologists and surgeons reviewed surgical guidelines and key publications for ALND surgical techniques and radiation oncology nodal contouring guidelines. Clinical photographs of surgical dissections were acquired intraoperatively for three patients undergoing level I-II ALND. Clips were placed to mark the apex of the dissection and for haemostasis. Radiotherapy CT-planning scans of patients were acquired post-operatively. The taskforce then reviewed the guidelines, clinical photographs and CT-planning scans aiming to reach a consensus on boundaries of the residual axillary nodal basin. Results: A number of key findings were agreed. The supero- medial limit of an en bloc Level I-II ALND is at the medial border of pectoralis minor inferior to the axillary vein. An apical clip placed in fat marking this boundary intra-operatively (upper limb usually abducted up to 90°) is not observed at the medial border of pectoralis minor on CT-planning scans (upper limb usually abducted > 90°) but laterally towards the superior aspect of Level I in all patients (Figure 1). This finding is explained by movement of the mobile axillary contents, including fat and clips, laterally in relation to pectoralis minor according to
increased upper limb abduction and scapula rotation. Also, while the apical clip and clips used for haemostasis are clearly distinguishable during surgery, it appears that once the wound is closed these may clump together making it challenging to differentiate between them on CT-planning scans.
Conclusion: Multidisciplinary discussion is crucial to understand the extent of ALND for individual patients. The residual axillary nodal basin following en bloc Level I-II ALND includes the axillary contents posterior to pec minor on CT-planning scans (Level II in contouring atlases) when patients are positioned with arms further abducted compared to abducted up to 90° during surgery. A dedicated contouring atlas for the residual axillary nodal basin after ALND may enable consistent contouring for radiotherapy planning, improved target coverage and avoidance of the dissected axilla. Keywords: MDT, ATLAS, AXILLA Toxicity and compliance to adjuvant concurrent chemo-radiotherapy for breast cancer: initial data from a randomized trial. Tabassum Wadasadawala 1 , Naseera Syeda 1 , Rajiv Sarin 1 , Rima Pathak 1 , Revathy Krishnamurthy 1 , Sushmita Rath 2 , Sudeep Gupta 2 1 Radiation Oncology, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India. 2 Medical Oncology, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India Digital Poster Highlight 4467
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