ESTRO 2025 - Abstract Book

S598

Clinical - Breast

ESTRO 2025

References: 1-Joseph K, Vos LJ, Gabos Z, Pervez N, Chafe S, Tankel K, et al. Skin toxicity in early breast cancer patients treated with field-in-field breast intensity-modulated radiotherapy versus helical inverse breast intensity-modulated radiotherapy: results of a phase III randomised controlled trial. Clin Oncol (R Coll Radiol). 2021;33(1):30-9. 2- Lee HH, Chen CH, Luo KH, Chuang HY, Huang CJ, Cheng YK, et al. Five-year survival outcomes of intensity modulated radiotherapy with simultaneous integrated boost (IMRT-SIB) using forward IMRT or Tomotherapy for breast cancer. Sci Rep. 2020;10(1):4342.

3759

Digital Poster Streamlining trial QA using simple metric to identify potential High Tangents for the ATNEC breast cancer trial (NCT04109079) Zohal nabi 1 , Patricia Díez 1 , Luke Gilling 1 , Sabreena Ahmed 1 , Louisa Buckley 1 , Elizabeth Miles 1 , Romaana Mir 2 , Carmel Anandadas 3 , Alison Ranger 4 , Indrani Bhattacharya 5 , Duncan Wheatley 6 , Andrea Marshall 7 , Janet Dunn 7 , Sophie Nicholls 7 , Amit Goyal 8 1 National Radiotherapy Trials Quality Assurance Group, Mount Vernon Cancer Centre, London, United Kingdom. 2 Department of Radiotherapy, Mount Vernon Cancer Centre, London, United Kingdom. 3 Clinical Oncology, The Christie Hospital, Manchester, United Kingdom. 4 Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, United Kingdom. 5 Department of Oncology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom. 6 Department of Clinical Oncology, Royal Cornwall Hospitals NHS Trust, Cornwall, United Kingdom. 7 Warwick Clinical Trials Unit, University of Warwick, Coventry, United Kingdom. 8 Oncoplastic Breast Surgery, University Hospitals of Derby and Burton NHS Foundation Trust, Derby, United Kingdom Purpose/Objective: The ATNEC Trial investigates whether axillary treatment can be safely omitted in patients with a complete pathological nodal response to neo-adjuvant chemotherapy. All participating institutions completed a comprehensive pre-accrual RT QA programme. During accrual, patients randomised to the ‘no axillary treatment’ arm were subject to retrospective plan review to monitor field placement for the use of high tangents (HT). The POSNOC trial validated use of base of clavicle (BOC) as a time efficient tool in defining HT [1]. ATNEC has implemented this metric to identify potential HT plans. The study aims to further investigate those plans identified as HT in terms of placement of the superior tangential border in relation to the breast CTV and dose to nodal levels 1 (L1) and 2 (L2). Material/Methods: In September 2024, all ATNEC patient plans submitted for the ‘no axillary treatment’ arm were selected for retrospective review to confirm protocol compliance. HT plans were defined as those with superior tangential border >5mm cranial to the BOC. A breast CTV was generated and L 1 and L2 lymph node CTVs contoured on all cases by an RTT in accordance with ESTRO Guidance [2]; and peer-reviewed by the ATNEC trial reviewing radiation oncologists. Lymph node PTVs were generated using a 5 mm isotropic expansion margin in line with the ATNEC guidelines. All HT cases and an equal number of standard tangent (ST) cases were reviewed for breast CTV coverage and L1 L2 dosimetric parameters: V50% , V80% ,V90%, V95% (optimal constraint), Dmean, and D0.5cc. Repeated measures ANOVA was used to compare dosimetric coverage of L1 and L2 between HT and ST plans across these parameters. Results: Fifty-two plans from 18 institutions were reviewed. 17/52 (32.7%) were identified as HT. Analysis demonstrated for all 17 plans cranial displacement of the field was required to cover the superior aspect of the breast CTV (Figure 1). On dosimetric review no significant differences were observed between ST and HT plans in L1 coverage (p=0.61), however HT plans resulted in a significantly higher coverage of L2 (p=0.0000015) (Figure 2).