2691 - Predictors of Acute Skin Toxicity in Patients Undergoing Hypofractionated Adjuvant Whole Breast Radiotherapy with VMAT or Helical Tomotherapy

Monday, September 30, 2024

3:00 PM – 4:00 PM ET

Location: Hall C

Screen: 19

Presenter(s)

Didem Karacetin, MD

Health Science University, Basaksehir Cam and Sakura City Hospital
Istanbul, Besiktas

M. Halici¹, H. Öner¹, T. Kapagan², and D. Karacetin¹; ¹Basaksehir Cam and Sakura City Hospital, Radiation Oncology Department, Istanbul, Turkey, ²Basaksehir Cam and Sakura City Hospital, Medical Oncology Department, Istanbul, Turkey

Purpose/Objective(s): Extensive research indicates that hypofractionated breast cancer radiotherapy improves cosmetic outcomes while maintaining local control. However, studies predicting toxicity in breast cancer patients receiving hypofractionated therapy alone are still limited. The aim of this study is the identification of predictive factors for acute skin toxicity in hypofractionated adjuvant whole breast radiotherapy. Materials/

Methods: A retrospective single-center study was conducted, including breast cancer patients treated from May 2021 to November 2023. Patients were treated with either VMAT or helical tomotherapy to deliver 40.05 Gy in 15 fractions to the whole breast with or without regional nodal irradiation(RNI), plus a 10 Gy boost to the tumor bed in 5 fractions. During radiation therapy and after the end of radiotherapy within 3 months, acute skin toxicity was monitored, utilizing the CTCAE v 4.0. Data including age, comorbidities, stage and treatment details were retrospectively evaluated. Univariate and multivariate analyses were conducted to identify potential predictive factors associated with acute skin toxicity.
Results: The study included 101 patients. The median age was 50 years (25-78 years). Treatment planning showed that 62 patients (61.4%) were planned for VMAT and 39 (38.6%) for helical tomotherapy. The study found that 54.5% of patients had a small breast size (mean; =1151 cm³), while 45.5% had a large breast size (mean; >1151 cm³). RNI was performed in 67 patients (66.3%). In the univariate analysis, only the breast volume (p<0.001) was significantly higher in cases of acute skin toxicity. No significant differences were found in acute skin toxicity between patients receiving or not receiving RNI (p=0.196) or between helical tomotherapy and VMAT treatment planning techniques (p=0.833). On multivariate analysis, breast volume was the only independent significant factor associated with the development of acute skin toxicity (p=0.001) (Table 1).
Conclusion: The study has confirmed that hypofractionated radiotherapy is associated with better cosmetic outcomes. However, it still shows that large breast volume is a significant predictor of acute skin toxicity even for hypofractionated treatments. Additionally, to our knowledge, this is the first study comparing two contemporary planning techniques, VMAT and helical tomotherapy, in terms of acute skin toxicity in hypofractionated radiotherapy. No significant difference in toxicity was observed between these two planning techniques. Table 1: Multivariate analysis with logistic regression for acute skin toxicity

Variables	Odds Ratio	P-value	95% CI
Chemotherapy	1.819	0.240	0.670-4.937
Hormone therapy	0.973	0.964	0.291-3.251
RNI	1.606	0.369	0.571-4.514
Planning techniques	1.482	0.402	0.590-3.720
Breast volume	0.183	*0.001*	0.065-0.516
Boost volume	1.270	0.630	0.480-3.358