2950 - Cosmetic Outcomes and Toxicity of 28.5 Gy in 5 Fractions Accelerated Partial Breast Irradiation: A Single-Institution Study
Presenter(s)
T. Jitwatcharakomol1,2, Y. Gokun3, S. J. Daniel2, M. Mestres-Villanueva2, R. Young2, J. M. Eckstein2, T. Y. Andraos2, E. Healy4, J. R. White5, J. G. Bazan Jr6, S. Beyer2, and S. R. Jhawar2; 1Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand, 2Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, OH, 3Center for Biostatistics, Department of Biomedical Informatics, The Ohio State University Wexner Medical Center, Columbus, OH, 4Department of Radiation Oncology, University of California - Irvine, Orange, CA, 5The Ohio State University Wexner Medical Center, Columbus, OH, 6Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA
Purpose/Objective(s): Accelerated partial breast irradiation (APBI) has been shown to result in non-inferior in-breast recurrence compared to whole breast irradiation in low-risk breast cancer patients across multiple randomized controlled trials. However, a single standard fractionation, dose, and technique of the external beam APBI is not well established. Herein we report the APBI outcomes using our institutional standard regimen.
Materials/Methods: This is a single-institution retrospective registry of early-stage breast cancer patients who underwent lumpectomy and APBI. The APBI regimen in this study consisted of 28.5 Gy in 5 fractions, delivered once daily on non-consecutive days to the lumpectomy cavity. This dose and fractionation was developed at our institution with our physics and dosimetry teams based on available literature and radiation biology modeling. Gross tumor volume (GTV) defined as lumpectomy cavity including seroma and clips. Clinical target volume (CTV) was expanded 1.5cm from GTV, and expanded another 5mm for planning target volume (PTV). The endpoints of interest included CTCAE v4.0 radiation toxicities, and physician-reported (Harvard) cosmesis.
Results: Between January 2021 and February 2024, 182 patients were reviewed. The median age was 66-year-old (Interquartile range (IQR) 60-72). APBI was administered to 186 lesions, including 4 patients with bilateral breast cancer. All patients received 3D conformal technique, and majority of patients (97.8%) were treated in the prone position, and 97.8% were either Estrogen receptor (ER) or Progesterone receptor (PR) positive. 96 patients had Oncotype Dx scores available, 67 (69.8%) were low risk (scores of 0-17) while 28 (29.2%) were considered as intermediate (scores of 18-30), and 1 patient (1%) was high risk (scores =31). The median GTV, CTV, and PTV of the treated lesions were 17.3 cc (IQR 11.5-26.3 cc), 103.9 cc (IQR 75.2-144.6 cc), and 181.3 cc (IQR 142.8-250.3 cc), respectively. Median follow-up was 2.2 years. Common acute grade 1/2 toxicities included dermatitis (26.6%), fatigue (62.1%), breast pain (19.2%), and breast edema (23.9%). At 6 months, common grade 1/2 late toxicities were fibrosis (48.9%), breast atrophy (42.0%), and skin hyperpigmentation (38.2%). No grade 3 or higher toxicities were observed. One year physician-reported cosmesis was available for 138 patients, with excellent or good cosmesis observed among 135 (97.8%) patients.
Conclusion: The APBI regimen of 28.5Gy in 5 fractions using 3DCRT in the prone position resulted in a low rate of acute toxicity and a high rate of excellent -good cosmetic outcome. This supports that 3DCRT is a reliable alternative to intensity modulated radiation therapy (IMRT) for APBI delivery. Long-term follow-up is warranted.