ESTRO 2024 - Abstract Book

S158

Brachytherapy - Breast

ESTRO 2024

Jose-Luis Guinot 1 , Cristina Gutierrez-Miguelez 2 , Norbert Mészáros 3 , Victor Gonzalez-Perez 4 , Miguel A Santos 1 , Dina Najjari 2 , Andrea Slocker 2 , Tibor Major 5 , Csaba Polgár 3 1 Foundation Instituto Valenciano de Oncologia IVO, Radiation Oncology, Valencia, Spain. 2 Catalan Institute of Oncology ICO, Radiation Oncology, Barcelona, Spain. 3 National Institute of Oncology, Radiation Oncology, Budapest, Hungary. 4 Foundation Instituto Valenciano de Oncologia IVO, Radiation Physics, Valencia, Spain. 5 National Institute of Oncology, Radiation Physics, Budapest, Hungary

Purpose/Objective:

The standard partial breast postoperative treatment for early breast carcinomas with multi-catheter interstitial brachytherapy (MIBT) requires 7-8 fractions in 4-5 days as used in the APBI GEC-ESTRO phase III trial. In 2017, the GEC-ESTRO Breast Working Group started a Phase I-II trial to study if very accelerated partial breast irradiation (VAPBI) using 3-4 fractions could be equivalent in terms of breast control and late complications.

Material/Methods:

We included 81 patients with low-risk invasive carcinomas managed with conserving surgery and treated postoperatively with high dose rate (HDR) MIBT. Mean age was 68 years (range: 51-90). Definitive pathology showed invasive ductal carcinoma in 70 cases (86%), invasive lobular carcinoma in 7 (9%), others in 4 (5%). Mean tumour size was 13 mm (range: 3-30), pT1a 36% (n=29), pT1b 36% (n=29), pT1c 21% (n=17), pT2 7% (n=6), margins were free by ≥2 mm in each case. Sentinel nodes were either pN0 (n=78) or pN0(i+) (n=3). Molecular subtype was luminal A in 64 (80%), luminal B in 11, HER2+ in 3, and triple negative in 3 patients, respectively. Histological grade was G1 in 37 (46%), G2 in 39 (48%), and G3 in 5 cases (6%). Proliferation index Ki-67 was <20 in 80% (n=65). Cases with lympho-vascular involvement or extensive intraductal carcinoma were not included. The trial started in August 2017, with 33 women (41%) receiving 4 fractions of 6.25Gy in 2-3 days, and, since no acute complications were reported, 48 subsequent patients (59%) were treated with only 3 fractions of 7.45 Gy in 2 days. In total, 71 cases (88%) were treated in two days. In July 2019 the trial was closed. Thirty-six women (44%) were implanted with a perioperative technique during the surgical procedure, and 45 (56%) postoperatively using CT or ultrasound to guide the plastic tubes. Mean time between surgery and MIBT was 65 days for postoperative cases, and 6 days for perioperative implants. The CTV was drawn in the planning CT, defining an estimated tumour bed (ETB) with the central tubes and clips, and adding a margin of 10-20mm. Median number of plastic tubes was 13 (range: 7-24), median number of planes 3 (range: 2-5). Final dosimetry showed median V100 of 86.8 cc (20-228cc) median V150 of 25.2 cc (range: 6-78.6 cc); median D90: 105.3% (range: 82-120%); median DNR: 0.30 (range: 0.23-0.41), median COIN: 0.74 (range: 0.56-0.86).

Three patients received chemotherapy, two trastuzumab, and 96% hormonal treatment.

Results:

Median follow-up is 58 months (range: 12-74), 66 months for the group of 4 fractions and 55 months for 3 fractions. Two breast recurrences (2.5%) have been recorded in the group of 4 fractions, at 37 and 60 months. The estimated 5-year locoregional control rate is 95.9%. Six patients died, only one due to metastasis of the breast cancer (HER+). Regarding acute toxicity, hematoma developed in 15 cases, more frequent after perioperative implantations. Some pain was referred in 14.8%, acute dermatitis in 9 cases and three cases of infection. Late effects as pigmentation changes in the entrance or exit of tubes was seen during the first months after the implantation,