Pre-operative SABR With and Without Caloric Restriction for Early Stage Breast Cancer

This study is testing whether combining pre-operative radiation (using a technique called SABR — stereotactic ablative radiotherapy) with a period of caloric restriction (eating fewer calories) before surgery for early-stage breast cancer is safe and may improve outcomes. There is some evidence that restricting calories temporarily can make cancer cells more sensitive to radiation. **You may be eligible if...** - You are 40 or older (or 50+ if you have triple-negative breast cancer) - You have confirmed early-stage breast cancer (DCIS or invasive) with a tumor 3 cm or smaller - Your cancer is in one location in the breast - Your lymph nodes appear normal on imaging or biopsy - You are in good general health (Karnofsky score 70–100) - Your BMI is 21 or above - You speak English or Spanish - You are not being considered for pre-operative chemotherapy **You may NOT be eligible if...** - Your cancer has spread to lymph nodes or other organs - Your tumor is larger than 3 cm - You have had prior breast radiation on the same side - You have had any prior treatment (radiation or chemotherapy) for this breast cancer - You have significant psychiatric illness that would prevent you from following the protocol - Your BMI is below 21 Talk to your doctor to see if this trial is right for you.