What is external beam therapy?

External beam therapy (EBT) is a commonly used cancer treatment (therapeutic radiology). Radiation is sent from a machine directed at the part of the body where cancer is present. The healthcare provider who oversees the treatment (radiation oncologist) will decide on the type of machine used.

External beam therapy uses a type of radiation called ionizing radiation. This destroys the cancer cells, but it can also harm healthy cells.

To give healthy cells time to heal, you will get small doses (fractions) of radiation at each treatment session. This helps protect the healthy body tissue around the diseased area.

Why might I need external beam therapy?

External beam therapy is used to treat cancer. It's the most common type of radiation therapy used to destroy cancer cells and slow tumor growth. Sometimes it's used as the main cancer treatment. Other times it's used after surgery or chemotherapy. When used after other treatments, it's called adjuvant therapy. 

What are the risks of external beam therapy?

EBT can harm a growing baby. So it's important for women not to get pregnant while having treatment. Not much is known about the effects of radiation on children conceived by men during radiation therapy. Because of this, healthcare providers advise men not to get women pregnant during and for some weeks after radiation treatment. Talk with your provider about this issue.

External beam therapy can have side effects. Most of these go away a few weeks or a few months after treatment ends. But some side effects can be lasting (permanent) and show up months or years later. The location, type, and severity of side effects depend on the body part treated and the amount of radiation used. Ask your healthcare provider about your risk for short-term and long-term side effects from your radiation treatment.

Radiation therapy can slightly increase your risk of getting another cancer. In general, the risk is low. It’s usually outweighed by the benefit of treating the current cancer. But the risk is there. Talk with your treatment team to help decide which kind of treatment is right for you.

As with any medical procedure, there are risks linked to the procedure itself. Ask your treatment team about the risks linked to your specific treatment. 

How do I get ready for external beam therapy?

External beam radiation has 3 parts:

• Simulation

• Treatment planning

• Treatment delivery

During the simulation your treatment team will figure out what position you will be in every time the treatment is given. Devices are made to make sure you are in the exact same position each time. Small marks are placed on your skin to guide the daily treatments. Marker seeds may be placed in the target tumor or organ. These seeds help the radiation therapist put you in the correct place during each treatment.

During the treatment planning, the treatment team uses a special computer program to set up the radiation dose that will be sent to the tumor. The plan chooses the radiation dose that will have the largest effect on the tumor and cause the least amount of harm to nearby tissues. The actual treatment can start after the simulation and treatment planning are done.

You will most likely have radiation treatment as an outpatient. This means you go home the same day. You will be asked not to have powder, deodorant, or jewelry near the treatment area. Your treatment team will let you know if you need to do anything special to get ready for your therapy. A typical schedule is to have therapy once a day for 5 days a week, over 2 to 9 weeks.

What happens during external beam therapy?

The treatment process usually takes 10 to 30 minutes each time. Much of the time is spent putting you in just the right position. The length of treatment depends on how the radiation is delivered and the size of the dose. Each treatment facility may have its own set of guidelines. But in general, external beam therapy follows this process:

You will usually get external beam therapy 4 or 5 times a week over several weeks.

Depending on the location of the cancer, you may need to remove clothing. If so, you will be given a gown to wear.

You will be carefully positioned so that the area under treatment will get the right amount of radiation. Special molds and other equipment may be used to keep you in the correct position.

Shields may be used to protect normal body tissues from the radiation.

Once the positioning and shielding have been set up, the treatment will begin. You will need to stay very still during the treatment. This is so the radiation beam will reach the cancer with the correct dose.

When EBT starts, the technologist will closely watch you on a screen in another room.

The treatment will be painless and will last for only a few minutes.

You will not see, smell, or feel the treatment.

You will not be radioactive after the treatment.

What happens after external beam therapy?

After each treatment, you may have tiredness (fatigue), sensitive skin at the radiation site, and emotional distress. Plan for extra rest and try to eat a healthy, well-balanced diet. Limit how much sun you get on sensitive skin areas. Use only lotions approved by your healthcare team. Your treatment team will have information on how to best manage physical side effects. You can ask for a referral to a mental health specialist to help cope with the emotions surrounding your diagnosis and treatment. Your treatment team has resources to help you.

The radiation oncologist will watch your progress and how the cancer responds to each treatment. They may change the radiation dose, number of treatments, or the length of treatment.

Once all treatments in your schedule are done, your healthcare team will let you know the follow-up schedule. You will need to return for follow-up assessments. These often include imaging tests and blood tests. These tests will tell them if the cancer is no longer present or if you need more treatment. You will need to make regular follow-up visits if the tumor is gone.

Next steps

Before you agree to the test or procedure make sure you know:

• The name of the test or procedure

• The reason you are having the test or procedure

• What results to expect and what they mean

• The risks and benefits of the test or procedure

• What the possible side effects or complications are

• When and where you are to have the test or procedure

• Who will do the test or procedure and what that person’s qualifications are

• What would happen if you did not have the test or procedure

• Any alternative tests or procedures to think about

• When and how you will get the results

• Who to call after the test or procedure if you have questions or problems

• How much you will have to pay for the test or procedure