This purpose of this study is to examine skin reactions (called radiation dermatitis) that occur during pencil beam scanning (PBS) proton therapy. The researchers will test a unique technique called "Spot Delete" to see if it can reduce skin reactions for breast patients treated with PBS. They will also use a special computer model to study how the energy of the proton beam (linear energy transfer) is related to these skin reactions. The study involves creating a treatment plan based on a CT scan, which helps guide the proton beam in the body. The clinical team uses this CT scan to find the best placement for the protons. The "Spot Delete" method prevents protons from stopping in the skin, which is thought to cause skin redness.

During the study, digital photos of patients' skin will be taken to assess the amount of redness, without revealing their identity. Patients will be given a self-report questionnaire and medical staff will document the skin reactions in the patients' medical charts. The degree of skin reactions will be compared against historical occurrence rates, and the location of any skin reactions that occur will be compared against the predicted location from the computer model. In this study, we aim to test the hypothesis that the "Spot Delete" technique in proton therapy reduces radiation dermatitis in breast cancer patients compared to historical data from patients who underwent regular proton therapy without the technique. To evaluate this, we will compare the extent of skin reactions in patients who receive proton therapy with the "Spot Delete" technique to historical data from patients who did not receive this treatment.

The effectiveness of the technique will be evaluated by measuring and documenting the degree of skin reactions in patients undergoing proton therapy with the Spot Delete technique. Digital photographs of the treatment area will be taken to assess radiation dermatitis using the treatment using the Common Terminology Criteria for Adverse Events (CTCAE) ver. 5.0 and using the Radiation Dermatitis Severity (RDS) scoring system. Radiation dermatitis will be assessed at baseline, weekly after every fifth treatment session, at the end of treatment, and at 2 post treatment follow-up appointments (e.g. 1-month and 6-months post treatment).These results will be compared to historical occurrence rates of skin reactions in regular proton therapy.

Inclusion Criteria:

• The patient must consent to be in the study and must have signed an approved consent form conforming to federal and institutional guidelines.
• Patients must be equal to or greater than 18 years old.
• The patient must have stage 0, I, II, or III breast cancer
• On histological examination, the tumor must be ductal carcinoma in-situ (DCIS) or invasive adenocarcinoma of the breast
• Surgical treatment of the breast must have been lumpectomy or mastectomy
• Patients must have an estrogen receptor (ER) analysis performed on the primary tumor
• Progesterone (PgR) analysis is desired but not mandatory
• No serious health conditions as determined by physician that would impact ability to complete treatment or impact skin in the area of treatment

Exclusion Criteria:

• Stage IV breast cancer
• Non-epithelial breast malignancies such as sarcoma or lymphoma
• Paget's disease of the nipple
• Prior breast or thoracic radiation therapy (RT) for any condition.
• Collagen vascular disease, specifically dermatomyositis with a Creatine phosphokinase (CPK) level above normal or with an active skin rash, systemic lupus erythematosis, or scleroderma.
• Pregnancy or lactation
• Psychiatric or addictive disorders or other conditions that, in the opinion of the investigator, would preclude the patient from meeting the study requirements.

Men are not eligible for this study