ESTRO 2024 - Abstract Book

S155

Brachytherapy - Breast

ESTRO 2024

The techniques used are both high-rate brachytherapy (HDR), low-rate brachytherapy (LDR) and pulsed brachytherapy (PDR), analysed in retrospective series, the most notable being the GEC-ESTRO trial, with an overall survival and locoregional recurrence-free survival above 90%, with good or excellent cosmetics in 70-80% of cases. The use of BT as a SCT has experienced a growth in the last 5 years.

Material/Methods:

Between 2009 and 2023, 77 treatments with salvage HDR BT have been carried out in our centre, 20 of them between 2009-2019, 43 between 2020-2022 and 14 from January 2023 to October 2023. Only the 63 patients treated up to and including 2022 were considered for our study. In order to make a good selection of patients who could benefit from a SCT, the following criteria were established, based on the GEC-ESTRO recommendations: age ≥ 50 years, tumours ≤ 2cm, invasive ductal carcinomas, low differentiation grade, without nodal involvement, time interval between first breast conserving treatment and recurrence ≥4 years, unifocal, absence of clinical skin infiltration, negative margins and SCT feasibility. In younger patients, and particularly in those with a triple-negative phenotype, the technique is possible taking into consideration that the results are lower than those achieved for older patients with a different molecular subtype. Our purpose is to show the experience of our center using a SCT with interstitial HDR BT. The perioperative procedure is conducted after tumour resection, placement of a guide tube deep in the cavity over the bottom markers and closure of the surgical field by the breast surgeons. More vector needles (9-18) are placed in several planes (2-4), depending on the breast volume, which are then replaced by plastic tubes. The next day, the plastic tubes are cut and sealed with Oncosmart™ tubes for the planning CT. For postoperative implants the needles are guided by ultrasound and the CT is performed the same day. An estimated tumour bed (ETB) is drawn above the central markers and the guide tube, with a margin of 15-20mm for the CTV, excluding pectoral muscle and 7-10mm of the skin. The fractionation used until 2019 was 8 fractions of 4Gy B.I.D., later moving to 7 fractions of 4.3Gy to perform the total treatment in four days. The constraints used are: D90 CTV >100% and <115%, DNR <0.35 (V150/V100), skin dose <70% and rib dose <100%. If the margins of the lumpectomy specimen are affected, a new local resection could be considered.

Results:

After a median follow-up of 74 months in the group of patients treated between 2009-2019 and 18.2 months in those treated between 2020 and 2022, no local recurrence was detected. The median age was 66 years (range 42 90). The acute toxicity was mainly hyperpigmentation in the area where the plastic tubes were placed and induration secondary to the combination of surgery and BT. In terms of chronic toxicity, 80-90% of patients have a good result, with residual fibrosis as the only sequelae, most asymptomatic. Cosmetic result is not the main goal due to the asymmetry produced by two surgeries and two radiations, but all patients choose this option to preserve the own breast and nipple.

Conclusion:

SCT is a safe and efficient alternative to mastectomy with good tolerance in terms of toxicity. It is essential to properly select those patients who can be suitable to accomplish the treatment. The most widely used technique with the greatest evidence of low incidence of recurrences is interstitial BT. In our experience, patients treated with SCT based on HDR BT have not experienced a second recurrence so far, although further follow-up is necessary, since most treatments were performed in the last 4 years. It is also worth noting the patient satisfaction preserving their breasts, with only residual fibrosis, a relevant aspect in the quality of life of women with breast cancer recurrences.