How Does Radiation Therapy for Cancer Work?

Treatment shrinks tumors, destroys cancer cells

A radiation oncologist comforts a cancer patient.

Treatment shrinks tumors, destroys cancer cells

Radiation therapy is a type of cancer treatment that uses beams of intense energy to damage the DNA of cancer cells to prevent them from growing and dividing.

Also called radiotherapy, radiation therapy has been in use for well over a century and is used to treat nearly every type of cancer, either by destroying cancer cells or shrinking tumors before surgery. In fact, more than half of people diagnosed with cancer will be treated with radiation therapy as the main treatment or in combination with other treatments, such as surgery, chemotherapy and immunotherapy.


“We treat just about every single type of cancer with a different radiation therapy, including brain tumorsthroat cancerslung cancersbreast cancerspancreatic cancer and prostate cancer,” says Prabhakar Tripuraneni, MD, a radiation oncologist at Scripps Cancer Center and Scripps Clinic.

What are types of radiation therapy?

There are two major types of radiation therapy: external and internal.

The most common is external radiation therapy, which uses a machine called a linear accelerator to direct radiation to a specific part of the body.

Internal radiation therapy uses radioactive materials placed inside the body to kill cancer cells. These materials are either placed near the tumor (brachytherapy) or travel throughout the body in the blood to attack cancer cells (systemic therapy).

The type of radiation therapy a cancer patient receives depends on many factors, including the type of cancer, the size of the tumor, where it is located and how close it is to vital organs and healthy tissue.


“Precision is key when using radiation to kill cancer cells or slow tumor growth in order to avoid damage to normal tissues,” says Ray Lin, MD, a radiation oncologist at Scripps Cancer Center and Scripps Clinic.

Safer, more precise radiation therapy

In recent years, major advancements in radiation therapy technology and imaging have resulted in more precise and targeted treatments, as well as safer and faster delivery methods.

“Radiation therapy has come a very long way. We now have technology where we can pinpoint very small tumors, even very large tumors, and give an equivalent cure to surgery many times,” says Dr. Lin.

Linear accelerators today have sophisticated imaging technology that allows physicians to target hard-to-reach tumors and treat many different types of cancers. Imaging technologies such as CT-guided radiation therapy allow for better visualization of tumors and surrounding anatomy during treatment planning and delivery. This enhances accuracy and precision in while sparing healthy tissues.

“We went from a 2D view of the tumor to 3D to 4D imaging that shows the tumor moving in all directions as the patient breathes,” says Dr. Lin. “We can turn the radiation beam on and off to as the tumor moves.”

“We can also take X-rays in real time and modify what we are doing,” says Dr. Tripuraneni. “It’s so much more precise that you can give a higher dose in fewer treatments.”

This is known as hypofractionation, which involves delivering higher doses of radiation over fewer treatment sessions. This can reduce the overall length of treatment by nearly half; for example, hypofractionated breast radiotherapy can reduce treatment time from 5-7 weeks to 3-4 weeks.

Combining radiation with immunotherapy

Radiotherapy has long been combined with surgery and/or chemotherapy to treat cancer. More recently, researchers have studied the effectiveness of combining radiation therapy with immunotherapy, which uses the natural power of the immune system to fight cancer. There are different types of immunotherapy treatments, including vaccines and antibody therapies. Radiation may enhance the immune system’s response to cancer, potentially improving treatment outcomes.

No matter what type of cancer is being treated, an individualized treatment plan is vital. Once radiation therapy is recommended, a highly specialized care team that includes a radiation oncologist, a medical physicist and a medical dosimetrist develops the treatment plan and adjusts it as needed along the way.


“Looking to the future, I believe that the integration of precision medicine with radiation therapy will represent a transformative shift towards highly personalized health care,” says Dr. Lin.

“By harnessing the power of predictive analytics, molecular profiling and advanced imaging, we will not just be treating cancer, but tailoring our interventions to the unique genetic makeup and tumor characteristics of each patient. This method will not only enhance the effectiveness of treatments, but also significantly reduce the side effects by targeting therapy more precisely.”

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