Age

50–any

Sex

ALL

Healthy volunteers

Not accepted

Invasive ductal carcinoma or favorable special histology confirmed by core biopsy.
Unifocal tumor ≤2 cm; estrogen receptor-positive and HER2-negative; grade 1-2; clinically node-negative (cN0).
Age ≥65, or age 50-64 when surgery is unsuitable or declined (capped at 10 of 30 participants).
Tumor ≥5 mm from skin and pectoralis; willing to receive adjuvant endocrine therapy.
Zubrod performance status 0-2; able to undergo MRI and FDG PET/CT; informed consent.

Multifocal or multicentric disease; pure DCIS; invasive lobular carcinoma \>10%; extensive intraductal component or diffuse calcifications.
Grade 3, triple-negative, or HER2-positive disease; nodal or distant metastases.
Prior ipsilateral breast radiation or excisional biopsy/lumpectomy; neoadjuvant chemotherapy.
Tumor \<5 mm from skin or pectoralis; inability to meet dose constraints or PTV \>60 cm³.
Connective tissue disease; prohibited other malignancy; pregnancy or lactation.
Pathogenic BRCA1, BRCA2, PALB2, or TP53 variant; investigator judgment that participation is inappropriate.

SOLIS: Single-Dose Radiotherapy With Omission of Lumpectomy for Intact Small Breast Cancers