Early and Intermediate Treatment Outcome After Postoperative External Beam Accelerated Partial Breast Irradiation in Patients With Early-Stage Breast Cancer.

Purpose: To prospectively evaluate early and intermediate outcome after accelerated partial breast irradiation (APBI) in patients early-with stage breast cancer.

Methods And Materials: Inclusion criteria were defined according to the APBI American Society for Radiation Oncology's ASTRO Evidence-Based Consensus Statement. The prescribed dose was 26 to 28 Gy in 5 fractions on 5 consecutive days. Regular follow-up visits with objective and subjective evaluation of treatment tolerance were performed after 0 and 2 weeks, 6 months, and at annual intervals.

Results: Between February 2017 and January 2020, 175 patients with breast conserving surgery met the inclusion criteria for APBI. Mean age was 65.7 years (range, 46-88). Thirteen percent of patients received a diagnosis with carcinoma in situ, 55%, 35%, and 37% with T1a/b/c, and 10% with T2 stages, respectively. The mean volume of planning target volume (PTV) was 119 cc (range, 45-465), the ratio of mean PTV: whole breast volume ratio was 21% (7%-53%). Mean follow-up was 42 months (median, 45, range, 0-67). Acute toxicity after 2 weeks was low with 69%, 26%, and 5% grade 0, 1, and 2. In addition, 1-, 2-, 3-, 4-, and 5-year follow-up data were available from 146, 134, 107, 73, and 25 patients. Patient-reported cosmetic outcomes were assessed excellent or good in 97.9%, 98.5%, 98.1%, 98.6%, and 100%. Regarding grade 2 toxicities, as by now 3%, 2%, 2%, 0%, and 0% G2 fibrosis, 1%, 1%, 0%, 0%, and 0% G2 atrophy, no G2 skin telangiectasia or breast edema occurred. So far, none of the patients have experienced G3 toxicity or higher. The remaining patients had grade 0 or 1 toxicity only. Five ipsilateral breast recurrences (1 marginally to PTV, 4 out-of-field) and 5 distant recurrences were recorded by March 2023. The 4-year in-breast recurrence rate was 2.5%. Eight patients died, with 2 of them from disease. For all patients, the 4-year overall, cancer specific and disease-free survival rates were 97.1%, 99.4%, and 95.3%, respectively.

Conclusions: We showed high early- and intermediate-term treatment tolerance and disease control of APBI using 26 to 28 Gy in five fractions in one week in carefully selected patients with early breast cancer. APBI is highly appreciated by patients and efficient, as an additional advantage for busy centers.