S304
Clinical - Breast
ESTRO 2026
continuous surface guidance (AlignRT). Target volumes were delineated according to contemporary ESTRO consensus recommendations, with a 5 mm margin applied to create the planning target volume (PTV). An intensity-modulated radiation therapy (IMRT) plan was created based on the simulation scan as the reference plan, utilizing six megavolt flattening-filter-free (6 MV FFF) photon beams. Treatment was delivered on a Varian Ethos linear accelerator equipped with HyperSight CBCT. Results: ART was delivered using the Fast Forward regimen of 26 Gy in 5 fractions in 25 patients (62.5%), and 27 Gy in 5 fractions in 15 patients (37.5%). Most patients presented with early-stage, predominantly hormone receptor–positive subtypes (70%), and grade I–II tumors (82.5%). Thirteen patients (32.5%) had left- sided breast cancer, while the remaining 27 (67.5%) had right-sided. In all patients and across all fractions, the adapted plan was selected for treatment as it consistently provided superior dosimetric parameters. ART significantly improved target coverage, with mean PTV V95% increasing from 92.7% ± 3.2% in scheduled plans to 98.1% ± 1.1% in adaptive plans (p < 0.0001). Dose constraints for all organs at risk were met in both scheduled and adaptive plans. For the ipsilateral lung, the mean V30% was 14.5% ± 3.8% for scheduled and 15.7% ± 4.2% for adaptive plans, remaining below the protocol threshold of V30% ≤ 17%. For left-sided cases, heart V25% was 1.10% ± 2.04% in scheduled and 1.09% ± 1.59% in adaptive plans, while LAD Dmax averaged 1.74 Gy ± 1.16 Gy (scheduled) and 1.89 Gy ± 1.89 Gy (adaptive) — all within recommended limits. Median follow-up was 7 months, during which two patients (5%) developed grade 1 erythema according
Figure 1. Comparison of PTV between scheduled and adaptive treatment plans
to CTCAE v5.0, with no ≥ grade 2 toxicity observed. Table 1. Patient and treatment characteristics
Conclusion: CBCT-guided ART proved feasible, efficient, and clinically safe, achieving superior target coverage while maintaining excellent organ-at-risk sparing and minimal acute toxicity. These findings should be
Made with FlippingBook - Share PDF online