Inclusion Criteria:

- Must sign study-specific, institutional review board (IRB) approved informed consent
form prior to study entry. Note consent by legally authorized representative is not
allowed for this trial.

- Must be female.

- Must be > = 18 years of age.

- Must have a life expectancy of at least 10 years based on age and co-morbidities but
excluding diagnosis of breast cancer.

- Must have pathology proven breast cancer. Pathology must be invasive ductal or
lobular carcinoma of the breast.

- Must meet stage III group criteria per American Joint Committee on Cancer (AJCC)
Staging manual 7th edition (see appendix II).

- Must be treated with proton therapy within 9 weeks after last surgery for breast
cancer (lumpectomy, re-excision of margins, axillary staging procedure or mastectomy)
OR if chemotherapy is given, it must be finished at least 2 weeks and not later than
8 weeks prior to PT.

- Must have had surgical treatment of the breast - either modified radical mastectomy
or lumpectomy. Re-excision of surgical margins is permitted.

Exclusion Criteria:

- Weight over 410 pounds.

- Non-epithelial breast malignancies such as sarcoma or lymphoma.

- Synchronous multifocal or bilateral invasive or non-invasive breast cancer.

- Surgical margins that cannot be microscopically assessed or are positive at
pathologic evaluation. (If surgical margins are rendered free of disease by
re-excision, the patient is eligible).

- Evidence of contralateral breast cancer that would require contralateral adjuvant
radiotherapy.

- Breast size exceeding the technical limitation of daily set-up reproducibility. This
may be center-specific and will be assessed at the discretion of the treating center.

- Women with post-surgical temporary breast expanders will require individual
assessment. Depending on the manufacturing product and other treatment
planning-specific details the patient may be eligible or may be deemed ineligible, as
determined by treating investigator.

- Prior history of breast cancer.

- Paget's disease of the nipple.

- Prior radiation to the breast or thorax.

- 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 at the time of proposed study entry. Women of reproductive
potential must agree to use an effective non-hormonal method of contraception during
therapy such as an intrauterine device or condom with spermicide.

- Psychiatric or addictive disorders or other conditions that, in the opinion of the
investigator, would preclude the patient from meeting the study requirements.

- Prior history of non-breast malignancies unless they have been disease free for 5 or
more years and are deemed by their physician to be at low risk for recurrence.
Further, patients who have the following cancers treated within the prior 5 years are
permitted: carcinoma in situ of the cervix, carcinoma in situ of the colon, melanoma
in situ, basal cell or squamous cell carcinoma of the skin.