Ultrahypofractionated partial breast irradiation following oncoplastic surgery: secondary analysis of a phase II trial.

Purpose: Although partial breast irradiation (PBI) is accepted as an effective and cosmesis-preserving technique for low-risk early-stage breast cancer following standard lumpectomy, data supporting PBI following oncoplastic surgery are sparse. We report prospective data in efforts to determine whether PBI can be safely utilized after oncoplastic surgery.

Methods: Patients with low-risk stage 0-1 breast cancer following successful lumpectomy with optional oncoplastic reconstruction were enrolled on a phase II trial. Patients were treated with a modified Florence regimen to 30 Gy in 5 fractions on the Varian Edge radiosurgery system using IMRT or VMAT. Presurgical MRI, post-operative seroma and surgical clips were used to assist target delineation. The effect of oncoplastic surgery on radiation dosimetry and Breast Cancer Treatment Outcome Scale scores were assessed using student's t-test for continuous variables and chi-square for categorical variables.

Results: From 2018 to 2022, 50 patients with 52 tumors were enrolled with 48% undergoing oncoplastic reconstruction. Although median PTV volumes were numerically larger in the oncoplastic group (266 cc vs. 223 cc), there were no statistically significant differences in PTV volumes, ratio of PTV to whole breast or mean heart or lung doses (p > 0.05). Mean baseline BCTOS aesthetic scores were 1.35 for standard lumpectomy vs. 2.52 for oncoplastic (p = 0.003). At long-term follow-up > 2 years, mean BCTOS aesthetic scores were 1.29 for standard lumpectomy vs. 1.35 for oncoplastic (p = 0.71). At a median follow-up of 46 months, there were no local recurrences.

Conclusions: When utilizing pre-treatment MRI, surgical clips and a relatively large PTV, PBI after oncoplastic surgery was safe and effective for appropriately selected patients. In combination with oncoplastic surgery, partial breast irradiation achieves excellent long-term cosmesis that improves over time.