Proton Therapy for Breast Cancer

Table of Contents
View All
Table of Contents

Proton therapy, also known as proton beam therapy, is a unique type of radiation treatment that uses high doses of radiation to kill cancer cells. Proton therapy is helpful in treating breast cancer because it can more precisely target tumors than traditional radiation. It also minimizes damage to the surrounding critical organs, like the heart and the lungs.

This article will describe what proton therapy is and how it may be beneficial for people with breast cancer. 

A middle-aged cancer survivor sits by the window and reflects on her life - stock photo


What Is Proton Therapy? 

Proton therapy uses charged particles called protons to target and kill cancer cells. Proton therapy is also known as proton radiation therapy, proton beam therapy, or intensity-modulated proton therapy (IMPT). Proton therapy is helpful for treating tumors that are near vital organs or regions of the body. 

External beam radiation (aims radiation directly at the cancer) is the most common type of radiation therapy for breast cancer. Proton therapy is a specialized kind of external beam radiation that is less likely to harm surrounding healthy tissue because it targets just the tumor in a focused way.

Why Breast Cancer? 

Breast cancer is a type of cancer that starts in the tissue of the breasts. Breast cancer cells usually form a tumor that can be seen on an X-ray or felt as a lump. The breasts are close to the heart and lungs, and radiation can cause damage to these vital organs. Proton beam therapy can help treat breast cancer while reducing the risk of radiation damage. 

What Is Proton Therapy for Breast Cancer?

Proton therapy is a precise type of radiation therapy that allows your medical team to better target cancer cells than traditional X-ray radiation therapy. Your medical team may consider proton therapy as part of your treatment plan for breast cancer if you have a large tumor, underwent a mastectomy, or when cancer cells have spread to nearby lymph nodes. 

Proton therapy can be used in breast cancers that have not spread beyond the region of the breast. Metastatic cancers—cancers that have spread to distant parts of the body—are not eligible for proton therapy. This is because proton therapy closely targets the cancerous tumor and cannot be used systemically (throughout the body). 

How Does Proton Therapy Work? 

Proton therapy works by using radiation to break the DNA in cancer cells to destroy them. 

During the appointment, your radiation technician will use a synchrotron machine to accelerate the protons. Speeding up the protons increases their energy and pushes them through a nozzle on the machine. The protons can then travel to a set depth of the body and deliver high doses of radiation. Because the depth can be specified, these protons do not go beyond the tumor. 

Proton Therapy vs. Standard Radiation

Proton therapy and traditional X-ray therapy share many similarities. They both attack and kill cancer cells by damaging the DNA inside the cell. The number of visits needed for proton therapy and X-ray radiation therapy is usually the same. 

Traditional X-ray radiation delivers beams of photons that reach both the tumor and the tissues beyond it. When photons damage healthy cells around the tumor, serious side effects can occur. 

The protons used in proton therapy have unique properties that healthcare providers can use to deliver the radiation to a specific depth in the body. When proton therapy is administered, all of the energy is released by the time it reaches the tumor site. Because no dosage of radiation goes beyond the tumor, proton therapy has fewer side effects and complications. 

Studies show that patients who receive proton therapy are significantly less likely to experience serious side effects than patients who receive X-ray radiation. Patients who undergo proton therapy are also more likely to continue performing their daily activities. The two types of radiation appear to have the same level of efficacy against cancer cells. 

It is important to note that proton therapy is more expensive than traditional radiation, and not all insurance policies cover it. 


Proton therapy is more precise than traditional radiation therapy. This means that it is better able to target the cancerous tumor without damaging the surrounding tissues and organs.

How Proton Therapy Can Help Treat Breast Cancer

Proton therapy has been found to be effective at treating breast cancer. Because the breasts are so close to vital organs, like the heart and lungs, proton therapy is able to treat the cancerous tumor without damaging these important structures. 

Benefits of Proton Therapy for Breast Cancer

There are several potential benefits of using proton therapy for breast cancer treatment. The proton beams used in proton therapy do not reach tissues beyond the cancerous tumor. This lowers the risk of normal tissues being damaged and cuts down on side effects. This is especially helpful for people with left-sided breast cancer because the tumor is so close to the heart. 

Proton therapy also uses a higher dose of radiation, giving it a better chance of destroying the tumor. Possible benefits of using proton therapy for breast cancer include:

  • Fewer side effects than traditional therapy
  • Decreased risk of damage to the heart and lungs
  • Painless
  • Can be used with other treatments such as chemotherapy

Types of Breast Cancer Proton Therapy Can Treat

Proton therapy can be used in breast cancers that have not spread to distant areas of the body. Once breast cancer has metastasized to other organs, proton therapy will most likely not be effective. This means that people with breast cancer in stages 1, 2, or 3 may benefit from proton therapy. 

Breast cancers that are locally advanced are also candidates for proton therapy. This means that cancer has spread but has stayed in the same region of the breast. This includes cancer cells in areas like the chest wall, chest skin, or lymph nodes under the arm. 

The following types of breast cancer may benefit from proton therapy:

Treatment With Proton Therapy: What to Expect

The first step in delivering proton therapy is to meet with your oncology team. Your team will discuss your treatment options and make recommendations based on your stage of breast cancer and overall health. 

Once you decide to move forward with proton therapy, your medical team will identify exactly where in the breast your tumor is located. This is done with a mapping process that uses magnetic resonance imaging (MRI) or computed tomography (CT). This appointment is known as a simulation appointment. Once your medical team has created a three-dimensional map of your tumor, they will use a computer program to calculate your dose of radiation and where to administer it. 

During a proton therapy appointment, you will go to a private treatment room and receive radiation on a specialized treatment table. Your medical team will likely place an immobilization device to keep your body in the same position. The entire appointment usually takes about 30 minutes. Most treatment protocols include five appointments per week for several weeks. 


A proton therapy appointment usually lasts for 30 minutes. Patients receiving proton therapy can expect to attend five appointments per week for several weeks.

Proton Therapy Side Effects

While proton therapy appears to cause far fewer side effects than traditional radiation therapy, side effects and complications are still possible. Any type of radiation must pass through the skin first, so changes to the skin are common. Possible side effects of proton therapy include:

  • Skin redness (similar to a sunburn)
  • Skin dryness and irritation 
  • Blisters
  • Swelling 
  • Fatigue
  • Temporary hair loss at the site 


Proton therapy is a unique type of radiation treatment that targets tumors and delivers a high dose of radiation to kill cancer cells. Proton therapy is able to target cancer cells without causing significant damage to surrounding tissues and organs. This is especially important for people with breast cancer because their tumors are close to vital organs like the heart and lungs. 

A Word From Verywell 

Going through the process of diagnosis and treatment for breast cancer is overwhelming and likely one of the most stressful times of your life. It may help to know there are always new therapies being developed to better treat breast cancer with fewer side effects. Talk with your healthcare provider about proton therapy and ask if your type of cancer is eligible for this treatment. 

Frequently Asked Questions

  • What is the success rate of proton therapy for breast cancer?

    Proton therapy is a highly successful treatment option. A 2019 study of patients who underwent proton therapy after mastectomy (surgical removal of the breast) found that participants had a three-year survival rate of 97.2%.

  • Is proton therapy better for breast cancer than other therapies?

    Proton therapy may be effective at treating breast cancer. Patients who have breast cancer in stages 1, 2, or 3 may be candidates for proton therapy. 

  • How long does proton therapy for breast cancer take?

    Proton therapy for breast cancer is usually administered five times per week for several weeks. 

  • Is proton therapy better than chemotherapy?

    Proton therapy is a different type of treatment than chemotherapy and both may be used together. Chemotherapy attacks and kills cancer cells, as well as healthy cells, in the body. Proton therapy is able to target a cancerous tumor directly without damaging surrounding tissues.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Memorial Sloan Kettering Cancer Center. Cancer treatments: What is proton therapy

  2. Jimenez RB, Hickey S, DePauw N, Yeap BY, Batin E, Gadd MA, Specht M, Isakoff SJ, Smith BL, Liao EC, Colwell AS, Ho A, Januzzi JL, Passeri J, Neilan TG, Taghian AG, Lu HM, MacDonald SM. Phase II Study of Proton Beam Radiation Therapy for Patients With Breast Cancer Requiring Regional Nodal Irradiation. J Clin Oncol. 2019 Oct 20;37(30):2778-2785. doi:10.1200/JCO.18.02366

  3. American Cancer Society. What is breast cancer?

  4. Chowdhary M, Lee A, Gao S, Wang D, Barry PN, Diaz R, Bagadiya NR, Park HS, Yu JB, Wilson LD, Moran MS, Higgins SA, Knowlton CA, Patel KR. Is Proton Therapy a "Pro" for Breast Cancer? A Comparison of Proton vs. Non-proton Radiotherapy Using the National Cancer Database. Front Oncol. 2019 Jan 14;8:678. doi:10.3389/fonc.2018.00678

  5. National Cancer Institute. Is proton therapy safer than traditional radiation?

  6. Penn Medicine. Breast cancer: How proton therapy is protecting hearts.

  7. MD Anderson Cancer Center. Proton therapy for breast cancer.

  8. Penn Medicine. What to expect during proton therapy.

  9. Penn Medicine. FAQs about proton therapy.

  10. Luo L, Cuaron J, Braunstein L, Gillespie E, Kahn A, McCormick B, Mah D, Chon B, Tsai H, Powell S, Cahlon O. Early outcomes of breast cancer patients treated with post-mastectomy uniform scanning proton therapy. Radiother Oncol. 2019 Mar;132:250-256. doi:10.1016/j.radonc.2018.10.002

By Carrie Madormo, RN, MPH
Carrie Madormo, RN, MPH, is a health writer with over a decade of experience working as a registered nurse. She has practiced in a variety of settings including pediatrics, oncology, chronic pain, and public health.