This is a single-center, prospective phase II clinical study designed to evaluate whether omission of postoperative radiotherapy is clinically acceptable in young patients with low-risk ductal carcinoma in situ (DCIS) following breast-conserving surgery. Eligible patients include women younger than 40 years with low- or intermediate-grade DCIS, tumor size ≤1 cm, negative surgical margins ≥3 mm, absence of comedo necrosis, and unifocal screen-detected disease. Patients in the radiotherapy omission cohort will undergo close surveillance after surgery, with endocrine therapy permitted according to physician discretion. The primary endpoint is 5-year ipsilateral breast tumor recurrence (IBTR).