PRISM Trial: Partial Breast Versus Whole Breast Radiation in Early Breast Cancer

Breast-conserving surgery followed by radiotherapy is a standard treatment for women with early-stage breast cancer. Whole breast irradiation (WBI) is the current standard approach, but partial breast irradiation (PBI), which treats only the area surrounding the original tumor, may reduce radiation exposure to healthy tissues while maintaining similar treatment effectiveness. The PRISM Trial is a prospective, multicenter, phase II randomized controlled trial that will compare ultra-hypofractionated PBI and WBI using the same radiation schedule of 26 Gy delivered in five fractions with intensity-modulated radiotherapy (IMRT). One hundred eligible women with early-stage breast cancer will be randomly assigned to receive either PBI or WBI after breast-conserving surgery. The primary objective is to compare acute treatment-related skin toxicity between the two treatment approaches using both clinician-reported Common Terminology Criteria for Adverse Events (CTCAE v6.0) and patient-reported outcomes (PRO-CTCAE). Secondary objectives include evaluation of early and late toxicity, dosimetric parameters, normal tissue complication probability (NTCP), and the relationship between radiation dose distribution and clinical toxicity over 12 months of follow-up.

Inclusion Criteria: * Women aged ≥45 years. * Newly diagnosed, histologically confirmed breast carcinoma, including Invasive Ductal Carcinoma (IDC), Invasive Lobular Carcinoma (ILC), or Ductal Carcinoma in Situ (DCIS). * Early-stage disease (T1-T2, node-negative \[N0\]), with no evidence of distant metastasis. * Hormone receptor-positive disease (ER and/or PR positive). * HER2-positive disease, provided patients have received or are receiving appropriate HER2-targeted therapy, as per institutional practice. * Patients who have undergone breast-conserving surgery with no tumor on inked margins or no residual disease following re-excision. Exclusion Criteria: * Age \