Five-year results of the very accelerated partial breast irradiation VAPBI phase I-II GEC-ESTRO trial.

Background And Purpose: 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 Cancer Working Group started a Phase I-II trial to study if very accelerated partial breast irradiation (VAPBI) using 3-4 fractions could be equivalent.

Material: 81 patients with low-risk invasive carcinomas underwent high dose rate MIBT. Mean age was 68 (51-90); 33 women received 4 fractions of 6.25 Gy in 2-3 days, and 48 subsequent patients 3 fractions of 7.45 Gy in 2 days, 36 perioperatively and 45 postoperatively.

Results: Median follow-up was 62 months, with 5-year actuarial breast recurrence of 3.4 % (two cases). One patient died due to metastasis. Pigmentation changes in the entrance of tubes remained visible only in 12.3 % in long term (skin G1 toxicity). Fibrosis or slight induration (G1) in 22.2 % and G2 in 9.9 %. No case of telangiectasia has been described. Cosmetic outcome is good or excellent in 95 % and fair in 5 %. Four tumors located in the retroareolar area showed nipple retraction.

Conclusion: VAPBI with MIBT using four fractions of 6.25 Gy or three fractions of 7.45 Gy in two or three days offers good local control, with a 5-year rate of fibrosis G2 similar to the GEC ESTRO phase III trial. VAPBI in two days is a good choice to decrease the total time of treatment, which is beneficial for the patient and reduces the workload.