BP03 Presentation Time: 4:18 PM

Purpose

The study aims to present the long-term results of 508 cases of early breast cancer treated with accelerated partial breast irradiation (APBI) using interstitial multicatheter high-dose-rate brachytherapy (HDR-BT) following breast-conserving surgery (BCS) in a single institution.

Materials and Methods

Between July 2006 and December 2020, a total of 514 cases of low-risk invasive and in situ carcinoma after BCS were treated with APBI using interstitial multicatheter HDR brachytherapy (MIB) at our department and 508 who met the inclusion criteria were analyzed. The inclusion criteria were: ZUBROD 0 or 1, age ≥50 years, pT1-2aN0 cM0, tumor size ≤3 cm, unifocal, invasive carcinoma without neuroinvasion or angioinvasion, with a minimal surgical margin of 2 mm or DCIS with a minimal margin of 5 mm, without extensive intraductal components, positive estrogen receptors. A total dose of 32 Gy in 8 fractions was delivered twice daily with a minimum 6-hour interval. The recommended dose constraints from the Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology (GEC ESTRO) were followed. The primary endpoint was local recurrence.

Results

The median age was 65 years (range 46-86 years). The median follow-up was 101 months (range 5-209 months). No serious complications occurred during the procedure and all patients completed the treatment without interruptions. The treatment was well tolerated. In the first 40 cases the 2D treatment planning was used, while in the subsequent cases - 3D treatment planning. The recommended dose-volume limits for the implant, planning target volume (PTV) and organs at risk (OARs) were met. The mean volume of the PTV was 74 cc, with the average coverage with the prescribed dose (PTV ref) of 94%. The mean conformity index (COIN) was 0.69, while the mean dose homogeneity index (DHI) was 0.67. There were no grade ≥ 3 complications. In the whole group, a total of 10 local recurrences (1.96%) were observed. In 3 cases distant metastases (0.6%) and ipsilateral breast tumor recurrence in 8 cases (1.57%) were observed. The 5- and 10-year overall survival (OS) was 97.5% and 96.6%, respectively. The 5- and 10-year disease-free survival (DFS) was 95.6% and 91.3%, respectively.

Conclusions

APBI with interstitial multicatheterhigh-dose-rate brachytherapy is a safe and effective treatment, associated with a good toxicity profile and low relapse rates. We believe that patient selection criteria should be revised and possibly expanded. However, further studies are required to validate this approach.