Abstract
Breast cancer is the most common noncutaneous malignancy in women. The prevalence increases with age such that nearly 7% of women in the United States over age 70 will be diagnosed with breast cancer. Radiation therapy (RT) is a standard component of the treatment course for women of all ages with breast cancer. RT is commonly encountered in the adjuvant setting for women with nonmetastatic disease, but also works for disease palliation in women with metastatic or recurrent disease. Different techniques for delivering RT for breast cancer include whole breast irradiation (WBI), accelerated partial-breast irradiation (APBI), and chest wall irradiation. Although these techniques often employ external beam radiation therapy (EBRT) delivered with photons, proton beam radiation therapy (PBRT) may also be used for each of these methods. Dosimetric breast cancer studies demonstrate clinical benefits of PBRT compared to photon EBRT. PBRT reduces the radiation dose delivered to the heart, particularly in women with left-sided breast cancer. This may subsequently reduce cardiac toxicity and associated cardiovascular disease. PBRT minimizes radiation dose to the lung and secondary tissues resulting in reduced pulmonary toxicity and secondary malignancies, respectively. PBRT offers superior target homogeneity and lymphatic coverage possibly leading to a lower risk of disease recurrence. A phase 3 prospective randomized clinical trial is currently being conducted to evaluate the efficacy of PBRT compared to EBRT with photons in patients with stage II-III breast cancer. Patients over age 70 with favorable stage I breast cancer may omit adjuvant RT. Elderly patients who are candidates for WBI, APBI and chest wall irradiation can receive PBRT and enjoy the same aforementioned benefits with potentially less toxicities. PBRT also plays a role in disease palliation and definitive therapy in patients who are not surgical candidates. In the elderly population, screening tests, such as the Timed Up and Go and G-8, can help determine which patients are suitable candidates for PBRT.