To analyze late toxicity after very accelerated partial breast irradiation (VAPBI)
for low-risk breast cancer.Methods: In this retrospective, observational, international
multicenter study (HDH F20220713143949), patients with low-risk breast cancer underwent
lumpectomy + vAPBI (high-dose rate multicatheter interstitial brachytherapy-MIBT).
VAPBI was performed with 4(4x6.2Gy/2d), 3(3x7.45Gy/2d) or 1 fraction (1x16Gy or 1x18Gy/1d).
Primary endpoint was late toxicity. Secondary endpoints were cumulative incidence
of breast cancer local relapse (LR) and distant metastatic relapse (DMR) and specific
(SS) and overall (OS) survivals. Prognostic factors for late toxicity were analyzed.From
01/2012 to 06/2022, 516 pts with early breast cancer were enrolled. Median follow-up
was 44 months [95%CI 39-46]. Median age was 71 years [40-100]. Median tumor size was
12mm [1-35]. VAPBI delivered 1, 3 and 4 fractions for 205pts (39.7%), 167pts (32.4%)
and 144pts (28%) respectively. 221 late toxicity events were observed in 168pts (32.6%)
(Fibrosis, dyschromia, pain and telangiectasia). Grade 2 and 3 late toxicities were
observed in 7.2 and 0.6% respectively (no G4) with no difference between 1 and ≥2
treatment days. CTV>50cc (p=0.007) and V150>40% (p=0.027) were prognostic factors
for G≥2 late toxicity. Four-year cumulative incidence rates of LR and DMR were 2%
[95%CI 0-3] and 1% [95%CI 0-2] respectively.VAPBI based on 1 or ≥2 days of MIBT represents
an attractive de-escalation of irradiation approach for low-risk breast cancer. Late
toxicity profile appears acceptable while early oncological outcome shows encouraging
local control. Longer follow-up is warranted in order to confirm these preliminary
results.
