2936 - Comparison of Simultaneous Integrated Boost and Sequential Technique in Hypofractionated Radiotherapy for Breast Cancer: Impact on Acute Skin Toxicity and Dosimetric Outcomes
Presenter(s)
E. Ercan Jr1, Z. Baskan2, G. Ozden2, T. Z. Sütcü2, T. Tasçi2, E. Akdeniz3, Z. Ozgen1, and M. F. Eren2; 1Department of Radiation Oncology, Marmara University School of Medicine, Istanbul, Turkey, 2Marmara University Pendik Education and Research Hospital Radiation Oncology Clinic, Istanbul, Turkey, 3Department of Medical Education, Marmara University Faculty of Medicine, Istanbul, Turkey
Purpose/Objective(s): A boost dose to the tumor bed during adjuvant whole-breast irradiation (WBI) following breast-conserving surgery (BCS) improves local control in breast cancer patients. This boost dose can be delivered using a simultaneous integrated boost (SIB) or a sequential technique. This study compares acute skin toxicity and dosimetric outcomes between SIB and sequential techniques in patients receiving adjuvant hypofractionated radiotherapy (RT).
Materials/Methods: A retrospective analysis was performed on patients diagnosed with breast cancer at clinical stages T0-3, N0-3, and M0 who underwent adjuvant hypofractionated RT following BCS between 2016 and 2024. All patients received a boost dose to the tumor bed, either as SIB or sequentially. Acute skin toxicities were assessed based on EORTC/RTOG toxicity criteria. A multivariate regression analysis was performed to identify factors associated with acute toxicity, while an independent samples t-test was used to compare the SIB and sequential boost groups. Statistical significance was defined as p < 0.05.
Results: A total of 202 patients were analyzed. The median age was 57 years (range 34-82). Among the patients, 37.6% (n=76) had Luminal A breast cancer, 44% (n=89) had Luminal B, 9.9% (n=20) had HER2+, and 5% (n=16) had triple-negative breast cancer. The median follow-up was 24.5 months. The median CTV breast volume was 1051 cc (IQR: 706-1358), and the median PTV boost volume was 30 cc (IQR: 19-45) The RT technique used VMAT (volumetric modulated arc therapy) in 55% of the patients (n=112) and IMRT (intensity-modulated radiation therapy) in 45% (n=90). Sixty-five percent of patients(n=113) received radiotherapy at 40 Gy in 15 fractions to the whole breast, with SIB dose to the tumor bed at 48 Gy in 15 fractions. Forty-five percent of the patients (n = 89) received radiotherapy at 40 Gy in 15 fractions to the whole breast, followed by a sequential boost dose to the tumor bed of 10 Gy in 5 fractions (n = 87) and 12 Gy in 6 fractions (n = 2). Grade 2-3 acute skin toxicity was observed in 34 patients. The multivariate analysis showed no significant differences in grade 2-3 skin toxicity between the SIB and the sequential boost group (p = 0.640). The only important factor associated with toxicity was the CTV breast volume (p < 0.001). Regarding dosimetric outcomes, breast CTV coverage (V95) was significantly higher in the SIB group (p < 0.001). For the heart, V25 was considerably lower in the SIB group (p < 0.001), while V8 showed no significant difference between the SIB and sequential group (p = 0.75). The mean LAD dose was also lower in the SIB group for patients with left-sided tumors (p = 0.002). Ipsilateral lung V5, V20, and contralateral lung V5 were significantly lower in the SIB group (p<0.001). The skin Dmax dose was considerably higher in the SIB group (p=0.025).
Conclusion: Our study demonstrated a significant dosimetric advantage of SIB compared to sequential treatment for hypofractionated radiotherapy in breast cancer, with similar acute skin side effects.