Types of Radiation Therapy for Breast Cancer

Radiation therapy, also known as radiotherapy, is sometimes used to treat breast cancer. It involves the use of ionizing radiation to kill cancer cells, either for curative purposes if a tumor is localized or palliative care to ensure comfort and quality of life if a malignancy cannot be cured. It can also be used in adjuvant therapy to prevent cancer recurrence after the tumor has been removed in a lumpectomy or mastectomy.

Not all women with breast cancer need radiation therapy. It is generally indicated in the following circumstances:

• After breast-conserving surgery to kill all remaining malignant cells so that the cancer does not return
• After a mastectomy if the tumor is larger than 5 centimeters (roughly 2 inches) or if nearby lymph nodes have evidence of cancer
• With stage 4 breast cancer, when the cancer has spread (metastasized) from the breast to other organs in the body

Broadly speaking, there are two types of radiation therapy used to treat breast cancer: external beam radiation and brachytherapy (also known as internal radiation therapy). Each has its specific purpose and indications.

Radiation is applied to cancer cells to impede their growth. Cancer cells are different from normal cells in that they are "immortal." Rather than undergoing apoptosis (programmed cells death) so that old cells can be replaced with new ones, cancer cells continue to multiply unimpeded. Moreover, they do so at an accelerated rate, allowing them to infiltrate and supplant normal tissues.

Radiation therapy works by damaging the genetic material of a cancer cell (DNA). By doing so, the radiation induces apoptosis and effectively kills the cancer cell. Beyond the tumor site, radiation can be used to clear cancer from nearby lymph nodes.

To minimize damage to nearby tissues, the affected area will first be mapped using a 3D imaging study, typically computed tomography (CT). This not only includes the tumor site but surrounding tissues, called margins, where cancer cells comingle with normal ones.

Once mapped, the tumor site can be irradiated from different angles either externally (with ionizing radiation beams) or internally (with encapsulated radioactive materials). Newer techniques are being developed that combine real-time imaging with the actual radiation procedure.

External beam radiation is the most common form of radiation therapy used in breast cancer. The radiation is delivered by a machine that emits a single high-intensity X-ray beam from several directions. The procedure is painless and relatively fast, but it can cause side effects.

The areas of irradiation can vary by whether you have had a mastectomy or lumpectomy and whether nearby lymph nodes are affected. The guidelines for external beam radiation can be broadly described as follows:

• If you have had a mastectomy and no lymph nodes are involved, radiation would be focused on the chest wall, the mastectomy scar, and the tissues where surgical drains were placed.
• If you had a lumpectomy, the entire breast would likely be irradiated (referred to as whole breast radiation) with an extra boost of radiation to the area where the tumor was removed (i.e., the tumor bed).
• If axillary lymph nodes are involved, radiation may be delivered in the armpit and, in some cases, to the supraclavicular lymph nodes above the collarbone and the internal mammary lymph nodes in the center of the chest.

Radiation can also be used with chemotherapy if a tumor cannot be surgically removed. In cases of inflammatory breast cancer, an aggressive form that spreads through lymph channels in the breast, radiation may be used after breast surgery and chemotherapy.

External beam radiation treatments would not start until you have healed from breast surgery or completed chemotherapy. The entire schedule of radiation therapy (called the course) is divided into daily treatments referred to as fractions.

Before radiation therapy begins, a radiologist will map the treatment area and, along with the radiation oncologist and possibly a dosimetrist, determine the correct dose and angles of irradiation. The oncologist may apply small ink marks or tattoos to your skin to ensure the radiation is focused correctly.

Speak with your oncologist in advance of the procedure to determine which, if any, ink marks will be permanent.

In some cases, accelerated breast irradiation (ABI) may be used. With this, stronger radiation doses are given over a shorter period of time. There are several types of ABI used when appropriate:

• Hypofractionated radiation therapy is used in women who have undergone a lumpectomy and have no evidence of lymph node involvement. While the procedure is similar to conventional external beam radiation, the dose is higher and the treatment course is reduced to three weeks.
• 3D-conformal radiotherapy involves a specialized machine that only treats the immediate tumor site rather than the whole breast. It is typically used after a lumpectomy in women with no lymph node involvement. Treatment is delivered twice daily for five days.
• Intraoperative radiation therapy (IORT) also involves specialized equipment and is intended for women with early-stage cancer and no lymph node involvement. For this procedure, a single large dose of radiation is delivered immediately after the lumpectomy while the incision is still open.

Because the external beam radiation is delivered through the skin, it can "spill over" and affect other tissues, including the lungs, ribcage, and surrounding muscles. It can cause both short- and long-term side effects, depending on the size of the dose, the duration of therapy, the location of the tumor, and your general health. Common short-term side effects include:

• Fatigue
• Breast swelling
• Skin changes (including redness, darkening, or peeling)

These side effects typically resolve once the therapy is completed, but some may take longer to improve than others. Skin changes in particular can take up to a year to normalize and, even then, may not fully return to their pretreatment state.

Long-term side effects may also occur due to the accumulative exposure to radiation. These include:

• Radiation-induced fibrosis: The hardening of breast tissue, which is often accompanied by decreased breast size and difficulty breastfeeding
• Brachial plexopathy: Localized nerve damage resulting in arm numbness, pain, and weakness
• Lymphedema: Lymph gland obstruction characterized by a swollen arm and surrounding tissues
• Radiation-induced osteopenia: Localized bone loss resulting in an increased risk of rib fracture
• Angiosarcoma: A rare complication in which radiation therapy triggers cancer

Brachytherapy, also known as internal radiation therapy, is used after a lumpectomy to irradiate the surgical cavity from within. The radiation is delivered through one or several tubes, called catheters, that are inserted through the skin of the breast. Radioactive seeds, pellets, tapes, or ribbons are then fed into the catheters and left for several minutes or days before being removed.

Brachytherapy can be used with whole breast radiation or on its own as a form of accelerated partial breast irradiation (APBI). There are two types of brachytherapy commonly used in breast cancer:

• Interstitial breast brachytherapy involves the placement of several catheters in the breast through which radiation sources are strategically placed in and around the tumor site.
• Intracavity breast brachytherapy, also known as balloon brachytherapy, is used after a lumpectomy to deliver radiation to the breast cavity via an inflatable balloon filled with radioactive pellets.

Another type of brachytherapy, known as permanent breast seed implant (PBSI), may be used in early-stage cancer. It involves the permanent implantation of low-dose radioactive seeds to prevent cancer recurrence. After several months, the seeds will lose their radioactivity.

As with external beam radiation, brachytherapy requires the careful mapping of the surgical cavity. Prior to the delivery of radiation, one or more catheters would be inserted into the breast either during the lumpectomy or in a separate procedure. The catheters are kept in place for the duration of therapy with a short length of tubing extending outside of the breast.

The type and dose of radioactive materials (typically iodine, palladium, cesium, or iridium) can vary by the treatment approach. They can range from ultra-low-dose rate (ULDR) seeds used for PBSI to high-dose-rate (HDR) implants commonly used for APBI.

Once the correct dose and coordinates have been established, the external catheter is connected to a machine, called an afterloader, which feeds the radioactive source through the catheters and removes them once the fraction is complete.

Intracavity brachytherapy is commonly performed over five days and involves two 10- to 20-minute sessions delivered six hours apart. Interstitial brachytherapy, less commonly used today, may be performed as an in-hospital procedure over one or two days.

Brachytherapy can cause many of the same side effects of external beam radiation, although they tend to be less severe.

Because brachytherapy involves one or more small incisions, there is an added risk of infection, particularly if the catheter site is not cleaned or is allowed to get wet. In some cases, a pocket of fluid, called a seroma, may develop beneath the skin and require drainage with a syringe and needle.

Proton beam therapy, also known as proton therapy, is an advanced method of radiation that poses less harm to surrounding tissues. Unlike high-intensity X-ray, which scatters radiation as it passes through a tumor, the radiation emitted in proton therapy does not travel beyond the tumor.

Instead, the charged particles, called protons, only release their energy as they reach their target. This reduces the so-called "exit dose" of radiation that can harm collateral tissues. Side effects are similar to other types of radiation therapy but are presumed to be less severe.

Most of the current studies are focused on its use in early-stage and advanced localized breast cancer.

Beyond the absence of clinical research, the cost and availability of proton therapy remain significant barriers to use. To date, there are only 27 centers equipped with proton beam cyclotrons in the United States; the cost of treatment is generally two to three times that of external beam radiation.