S315
Clinical - Breast
ESTRO 2026
the WB_PTV (Breast volume, V95%, V48GY, Dmax) and the boost_PTV (Boost Volume, V 95%_b, V 105%b, V
107 % b, V110%b and Dmax boost) were analyzedASAE was assessed clinically and
photographically before radiotherapy, weekly during treatment, and at 1 and 6 months post-radiotherapy according to CTCAE v5.0 criteria.Longitudinal variations in ASAE were assessed using the Friedman test, and the correlation between ASAE grades and dosimetric parameters was explored through Spearman and the χ 2 test. Results: A total of 85 patients were analyzed (34 local RT(40%), 50 RLNI (60%)).The evolution of ASAE over the defined treatment timeline is summarized in Table 1. The highest toxicity was observed during the 3rd week of treatment(p<0.000), with no grade 3 or 4 ASAE reported throughout the follow-up period.
In univariate analysis, breast volume > 800 cc (p = 0.000), V48 Gy > 25% (p = 0.002), and Dmax > 50.2 Gy (p = 0.000) were significantly associated with grade 2 acute skin adverse events, whereas neither regional lymph node irradiation nor boost volume demonstrated a significant correlation (Table 2). Conclusion: 3D-HFRT with a SIB was associated with low rates of ASAE, with peak reactions in week 3, underscoring the need for close monitoring. Breast volume was the main dosimetric predictor of grade ≥ 2 radiodermatitis. Excellent boost dose homogeneity was achieved despite expected whole-breast heterogeneity. These results support the feasibility, safety, and tolerability of HFRT 3D-CRT SIB for local and RLNI. Keywords: Simultaneous integrated boost, Hypofractionated RT Digital Poster 4026 Tolerated Yet Tested: Skin Reactions and Esophageal Dose Thresholds in Hypofractionated Breast RT Sumerya Duru Birgi 1 , Yasemin Celik 1 , Oguzhan Bascik 1 , Yunus Babayigit 1 , Pantea Bayatfard 1,2 , Yakup Arslan 1 , Hatime Arzu Yasar 3 , Serap Akyurek 1 1 Radiation Oncology, Ankara University, Ankara, Turkey. 2 Radiation Oncology, Denizli Onkomer Oncology Center, Denizli, Turkey. 3 Medical Oncology, Ankara University, Ankara, Turkey
Mean target coverage (V95%) for the whole breast and tumor bed was 99,28% ± 0,93 SD and 99,74% ±,89 SD, respectively , with acceptable hot spots (MeanV105% = 1,2% ± 1,1; V107%=0,03 % ± 0,27 for the whole breast). The maximum dose (Dmax) was located within the boost PTV in 97.7% of cases.The mean breast volume and Dmax were significantly higher in patients with ASAE grade 2. (Table 2).
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