Radiation Therapy

Many breast cancer patients are treated with radiation therapy. This type of therapy uses radiation beams to damage cancer cells and shrink tumors. When treating early-stage breast cancer, radiation therapy is often given after surgery to destroy any remaining cancer cells. This helps lower the risk of recurrence. Radiation therapy can also be used to treat breast cancer that can’t be removed with surgery or metastatic breast cancer.

At Siteman, Washington University radiation oncologists treat patients with the safest, most advanced forms of radiation therapy. Our facility houses every type of radiation therapy machine and tool available, so your care team will be able to match you with a radiation treatment plan that is ideal for you.

What is it like to receive radiation therapy?

It’s normal to have lots of questions before beginning radiation therapy. Patients sometimes worry that receiving radiation will be painful or that the treatment will make them “toxic” in some way. It can also seem daunting to fit regular therapy appointments into your daily schedule.

While your concerns are certainly valid, the truth is that radiation therapy is painless. In fact, patients can’t even feel the radiation beam. It only takes a few minutes to deliver the treatment. Oftentimes, ensuring that both the patient and the machine are in the correct positions takes longer than actually conducting the therapy. Still, this careful planning is crucial for achieving the best possible results.

Your care team at Siteman will work hard to ensure that you move through the treatment process as smoothly as possible. Our specialists focus on minimizing side effects and helping patients maintain their quality of life, both during and after treatment.

What forms of radiation therapy are used to treat breast cancer at Siteman?


External beam radiation

Ninety-five percent of radiation treatment at Siteman is external beam from outside the body. Washington University Physicians at Siteman use CT images to plan where the radiation will be delivered and what dosage to give. Radiation is given daily, and usually over several weeks.

When appropriate, our physicians will use MRI technology to guide the delivery of radiation. Radiation oncologists at Siteman were the first in the world to develop this technique and use it to treat patients. Patients who receive MRI-guided radiation therapy often have a smaller or more limited disease; the MRI ensures that the radiation fully meets its target. MRI-guided radiation sessions are longer in duration than traditional, external beam treatments.

Internal radiation

Called brachytherapy, this type of radiation is good for smaller primary tumors that have not yet impacted the lymph nodes. The radiation oncologist will insert a multi-channel applicator into the breast at the site of the tumor. The applicator stays in place for 5 days and delivers an intense radiation dose twice a day. The use and artful placement of the applicator sculpts the radiation dose away from adjacent ribs, skin and organs.  Siteman is a Center of Excellence for brachytherapy.

Other radiation treatments

Additional radiation-related treatments useful to breast cancer patients include:


This novel therapy not used elsewhere in the St. Louis region involves heating superficial breast tissue so cancer cells will respond better to radiation treatment, especially for recurrent chest wall or inflammatory breast cancer. It increases the benefit of the radiation therapy without upping the radiation dosage.

During hyperthermia, the breast tissue is heated to a temperature of approximately 104 degrees Fahrenheit. While this may sound very hot, patients usually tolerate it well. It’s not so hot that the skin feels burned. The heat is produced by ultrasound and microwave technologies that are targeted to a small area of tissue.

Hyperthermia is used for patients who have recurrent or more complex cases of breast cancer.

Proton beam

Siteman has the only proton facility in Missouri. Protons are positively charged particles that can shrink tumors in the same way regular radiation beams can. The difference is that a proton beam, unlike an X-ray beam, can be stopped at a certain depth. This limits the body’s exposure to radiation, protecting the internal organs. It is only applicable to specific cases of breast cancer, mostly for patients with recurrent disease and prior radiation treatments.

Radiation treatment plans

At Siteman, we are careful to customize each patient’s radiation treatment plan to the shape and extent of their disease. There are several tiers of treatment available, with each tier requiring a longer duration of treatment.

Accelerated Partial Breast Irradiation (APBI) 

This is typically used when a cancer is contained to only a portion of a patient’s breast. Treatments usually:

  • Are conducted through brachytherapy or MRI-guided external beam radiation
  • Last a week or less

Entire breast 

In some cases, radiation will be given to the entire area of the breast. Some patients opt for this level of treatment for extra reassurance that all of the cancer has been “caught.” Treatments

  • Are always done with external beam technology
  • Seldom require MRI-guidance, which leads to shorter treatment sessions
  • Last at least three weeks

Comprehensive treatment

If cancer has spread to regional lymph nodes, or if a patient has a large or inflammatory breast cancer, radiation will be extended to:

  • Any residual breast tissue left behind after a mastectomy
  • The chest area
  • Lymph nodes

This type of treatment is always done as external beam. It usually lasts from 5 and a half to 6 and a half weeks, although clinical trials are studying shorter durations of treatment.

Some patients who receive comprehensive treatment may also benefit from proton beam radiation therapy.

Limiting the impact of radiation on the body

At Siteman Cancer Center, we do our utmost to ensure that radiation therapy is as safe as possible for our patients. For breast cancer patients, one of our biggest concerns is keeping radiation beams away from the heart. Fortunately, Washington University Physicians at Siteman have collaborated with physicians in the cardiology department to found the Cardio-Oncology Center of Excellence, a group committed to preventing cardiovascular side effects in cancer patients and devising innovative treatments for side effects that do arise.

Some of the methods our radiation oncologists use to protect the heart include:

  • Using partial breast irradiation whenever possible. This technique has no direct exposure to the heart.
  • Asking patients to hold their breath while radiation is being delivered, which helps move the heart out of the way. Our radiation machines can be synced up to our patients’ lungs and will only emit radiation when the patient is not breathing. Patients do not need to hold their breath for a long time: the machines can deliver radiation in 20-second intervals if needed.
  • Positioning patients on their stomachs to limit exposure to the heart.
  • Intensity modulated radiation therapy, which can help minimize exposure to other parts of the body.

Why Siteman?

Siteman’s radiation oncology team has pioneered new methods that target breast tumors while sparing surrounding healthy tissue. They often use MRI to help guide radiation therapy treatments in real time, which allows the team to see where the dose is being delivered. From there, they decide whether adjustments are needed.

Radiation oncology has active trials focused on minimizing the duration of treatment and the amount of radiation a patient receives. The goal of these trials is to reduce long-term side effects and ensure that no patient is over- or undertreated. Siteman is a leader in using shorter durations of radiation therapy for breast cancer and yielding the same – or better – results.