S7
Track-Topic
ESTRO 2026
Purpose/Objective: The risk of breast tumour recurrence following breast conserving surgery is highest around the index quadrant of the primary tumour. Partial breast irradiation is an option for women with early breast cancer. We report on a method of delivering partial breast irradiation using interstitial multicatheter high- dose-rate brachytherapy. Material/Methods: Women above the age of 50 years, with newly diagnosed unicentric invasive breast carcinoma measuring 3cm or less in maximal diameter, with negative surgical resection margins, were enrolled onto this single centre, single-arm, prospective trial. Exclusion criteria included lobular histology, lymphovascular invasion, HER-2 receptor positive tumours, hormone receptor negative tumours, axillary nodal involvement and metastatic disease. Enrolled patients underwent partial breast irradiation using interstitial multicatheter high-dose-rate brachytherapy to a dose of 34Gy in 10 fractions over one week. The post-surgical seroma cavity was identified on ultrasound imaging and catheters were implanted in multiple parallel planes under a general anaesthetic using the Elekta Breast CT/MR Template. Treatment planning was performed using Oncentra Brachy software. The primary outcome was the rate of ipsilateral breast tumour recurrences analysed in the as-treated population. Secondary outcomes were overall survival and progression free survival. Results: Between November 2011 and March 2021, 147 women were enrolled, and 144 received the intended treatment. Median age at date of enrolment was 62 years (range, 48-87 years). 135 patients (94%) had an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0. 134 patients (93%) had stage pT1 tumours and 10 (7%) had stage pT2 tumours. The median primary tumour size was 10mm (range, 1.5- 26mm). The median PTV volume was 43.9cc (range, 8.3-131.6cc) and the median number of catheters implanted was 14 (range, 8-28). 6 patients (4%) received adjuvant chemotherapy, and 104 patients (72%) received adjuvant endocrine therapy. At a median follow-up 7.39 years, the 5-year and 7-year Kaplan-Meier estimated ipsilateral breast tumour recurrence rates were 2.1% (95% confidence interval [CI], 0.7-6.4%) and 3.3% (95% CI, 1.2-9.0%), respectively. The 5-year and 7-year estimated overall survival rates were 99.3% (95% CI, 94.9-99.9%) and 99.3% (95% CI, 94.9-99.9%), respectively. The 5-year and 7-year estimated progression-free survival rates were 94.3% (95% CI, 89.0-97.1%) and 92.2% (95% CI, 85.8-95.8%), respectively. Conclusion: Accelerated partial breast irradiation delivered using multicatheter high-dose-rate brachytherapy is an
Conclusion: This multicenter analysis revealed that the distance between the SAVI applicator and adjacent OARs significantly influences dose constraints in APBI. When the applicator is positioned close to the skin or chest wall, the corresponding OAR doses tend to increase, potentially complicating the achievement of clinically acceptable treatment plans. Although the impact on PTV_EVAL coverage was relatively minor, minimizing proximity to OARs during applicator placement may be crucial for optimizing dosimetric outcomes. These findings highlight the importance of pre-implant imaging assessment and careful applicator positioning to ensure both effective target coverage and OAR sparing in APBI using SAVI. Keywords: APBI, SAVI, References: Yoshida M. Yoshimura R. Notake R et al., Feasibility of accelerated partial breast irradiation with strut- adjusted volume implant brachytherapy in Japan focusing on dosimetry and acute toxicity: a Japanese multi-institutional prospective study. Breast cancer. 2024;31:75–83. Accelerated partial breast irradiation using interstitial multicatheter high-dose-rate brachytherapy: Efficacy results of a phase II prospective study George Cosman 1 , Lincoln Dinh 1 , Zoi Hei Wong 2 , Peter Graham 1 , Andrej Bece 1 , Gina Hesselberg 1 , Yaw Chin 1 1 Department of Radiation Oncology, St George Hospital, Sydney, Australia. 2 School of Medicine, University of New South Wales, Sydney, Australia Digital Poster 1472
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