Adjuvant accelerated partial-breast irradiation of early-stage breast cancer using stereotactic approach - methodology, technical challenges and early results of prospective randomized trial.

Background: The adjuvant radiotherapy (RT) of the early-stage breast cancer patients as local treatment aims to eliminate potential microscopic residual disease in the surgery bed or satellites in its neighborhood. Based on published studies, accelerated partial breast irradiation (APBI) is recommended for strictly selected patients. The aim of this single-institution prospective randomized study was to compare the targeted APBI delivered by stereotactic approach with the currently more commonly used accelerated whole breast irradiation with the boost to the tumor bed in terms of feasibility, safety, tolerance, and cosmetic effects.

Materials And Methods: Early-stage breast cancer patients after partial mastectomy were screened for eligibility. The inclusion criteria were age > 50 years, non-lobular carcinoma histology, size 2cm, negative margins 2mm, L0, ER-positive, BRCA negative. Enrolled patients were equally randomized into two arms according to radiotherapeutic regiment - external APBI (5× 6 Gy) and accelerated whole breast irradiation with the boost (15× 2,67 Gy + 5× 2 Gy). These preliminary results of the ongoing study evaluated the first 57 from 84 planned patients.

Results: The median age was 65 years. The tumors were of grade 1 in 60 % of patients, the median size of 9mm and 70 % were classified as invasive ductal carcinoma. Statistical significant differences between the groups in baseline characteristics were not observed. A total of 29 patients was enrolled in the APBI group by the end of 2020. All enrolled patients were evaluated one month after RT. A total of 40 (70,2 %) a 33 (58 %) had examinations 3 and 6 months after RT, respectively. Toxicity evaluation showed statistically significantly fewer acute adverse events in the APBI group in terms of skin erythema, desquamation, skin tenderness, dryness, edema, pigmentation, breast pain and fatigue. Late toxicity evaluated in 3 and 6 months after RT was significantly higher in the control group. The cosmetic effect (independently evaluated by a physician, nurse and patient) was more favorable to the APBI group.

Conclusion: The technique using the principles of targeted radiotherapy turned out to be a less toxic and easier feasible approach for adjuvant radiation of early-stage breast cancer patients. Consequently, the presented study increases the level of evidence for RT-indicated patients to the establishment of external APBI into daily clinical practice.