S337
Clinical - Breast
ESTRO 2026
to 40 Gy in 15 fractions after five years of follow-up (1). This study aims to determine the effectiveness of IMRT and VMAT as potential alternatives to the field-in-field (FiF) technique in ultrahypofractionation for BC. The investigation focuses on the non-inferiority of these techniques in terms of organ-at-risk (OAR) sparing and target coverage, as well as the clinical implications of utilizing the Acuros XB (AXB) algorithm compared to the Analytical Anisotropic Algorithm (AAA). Material/Methods: Fifteen patients with early-stage BC were retrospectively selected for this study. The delineation of the CTV and OARs followed the ESTRO guidelines, with the FAST-Forward protocol applied for defining the CTV to PTV margin. The total prescribed dose was 26 Gy, delivered in 5 fractions. Treatment plans employing the VMAT technique with flattening filter free (FFF) beams and the AXB algorithm were recalculated with AAA, maintaining constant monitor units. These plans were then converted to IMRT and recalculated with both AXB and AAA. Dose constraints for OARs and PTV limits, along with the conformity and homogeneity indices, were compared across the various techniques. The clinical impact of dosimetric differences was assessed by comparing tumor control probability (TCP) and normal tissue complication probability (NTCP) values. Results: PTV coverage, homogeneity, and conformity were comparable between IMRT and VMAT, regardless of the algorithm (AXB or AAA). The V105% constraint was unmet by the AAA algorithm alone, while V107% and Dmax were within optimal parameters. For the heart, V25% was optimally respected for all techniques, but V5% favored IMRT. Ipsilateral lung V30% met mandatory criteria with no significant difference between techniques, while IMRT showed better sparing of contralateral OARs (V5%) and significant spinal cord protection (p < 0.001). NTCP for the heart, lung, and spinal cord was negligible irrespective of the algorithm employed, while TCP was slightly higher with AXB (0.3% for VMAT, 0.37% for IMRT). Table1: Dosimetric parameters for target coverage and OARs, calculated using AAA and AXB in IMRT and VMAT plans
Conclusion: ML-based CO assessment from photographs is feasible and surpasses the current BCCT.core benchmark. Integrating clinical and patient-reported data enhances performance, reflecting the multifactorial nature of CO. These findings support the development of a selfie-based assessment tool for breast cancer follow-up, combining patient empowerment with objective outcome monitoring. References: https://ascopubs.org/doi/pdf/10.1200/JCO.20.01363htt ps://ascopubs.org/doi/pdf/10.1200/JCO.22.00451https: //www.sciencedirect.com/science/article/abs/pii/S0933 365707000206https://www.thelancet.com/action/sho wFullText?pii=S0140673620309326 Keywords: Cosmetic outcome, Machine Learning, Breast Cancer Clinical implications and evaluation of IMRT and VMAT in ultrahypofractionated breast cancer: dosimetric and radiobiological analysis with AAA and AXB Hela Ayouni 1,2 , Semia Zarraa 3 , Asma Ghorbel 3 , Khedija Ben Zid 3 , Sarra Saidi 3 , Bilel Daoud 4 , Lotfi Ben Salem 2 , Chiraz Nasr 3 1 Medical physics, Higher Institute of Medical Technologies of Tunis, Tunis, Tunisia. 2 Department of Medical Physics, Salah Azaiz Institute, Tunis, Tunisia. Digital Poster 4780 3 Department of Radiation Oncology, Salah Azaiz Institute, Tunis, Tunisia. 4 Department of Imaging physics research, MD anderson cancer center, Texas, USA Purpose/Objective: Ultrahypofractionation has emerged as a new paradigm in breast cancer (BC) radiotherapy following the findings of the FAST-Forward trial, which demonstrated that 26 Gy in 5 fractions is non-inferior
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