Phase 1/2 REPEAT tests accelerated partial-breast re-irradiation (aPBI) using external-beam radiation.

Dartmouth-Hitchcock Medical Center is running this prospective Phase 1/2 study to see whether re-irradiating only the partial breast (accelerated partial-breast irradiation, aPBI) yields acceptably low acute toxicity and preserves in-breast local control after a second ipsilateral breast cancer. The intervention is external-beam aPBI re-irradiation delivered with VMAT (volumetric modulated arc therapy), a planning/delivery approach that “sculpts” dose around a smaller target volume to reduce exposure to normal breast, heart, and lung; this is a device/technique trial rather than a pharma drug trial. Eligible patients have a histologically confirmed second ipsilateral breast cancer occurring more than 1 year after prior breast-conserving therapy with radiotherapy, and the protocol highlights lower-grade (grade 1–2) and ER-positive disease. The exploratory angle is cosmesis—important because re-irradiation can trade local control for fibrosis, pain, or poor breast appearance if the treated volume is too large. Today, many patients with an in-breast recurrence after prior whole-breast radiation are steered toward mastectomy (often with endocrine therapy for ER+ tumors), so this study probes whether a repeat breast-conserving approach plus focused re-irradiation can be a practical alternative for selected patients.