What is radiation therapy?

Radiation therapy, also called radiotherapy, is the branch of medicine that deals with the treatment of cancer by delivering high-energy beams directly to a tumor, or intended target.

Radiation therapy is a common form of treatment for cancer today. According to the Cancer Management, two out of three cancer patients will receive radiation therapy—either alone or in combination with other treatment approaches, such as surgery and chemotherapy. Each case is unique and your physician is the best person to decide on the suitability of radiation therapy for your treatment.

Radiation therapy has two equally important goals: to control the growth of the tumor and to do so while minimizing exposure to the surrounding normal, healthy tissue. Radiation therapy is broadly divided into external beam radiation therapy (EBRT), where radiation is delivered to the target from an external machine, and Brachytherapy, where radiation is delivered by placing the radiation source inside the body near the intended target. Both techniques are used for treating a large variety of tumor types.

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How Radiation Therapy works?

Radiation therapy, also known as radiotherapy, uses a focused beam of energy to damage cancerous cells while minimizing exposure to healthy tissue. Radiation damages the DNA in cancer cells, which interrupts their ability to reproduce, causing them to die and the tumor to shrink. Normal cells can recover from radiation more easily.

Treatment is delivered to the target site with a machine called a linear accelerator, or linac. The linac generates a high-energy beam, which is delivered from many different angles, to target each part of the tumor and deliver the prescribed amount of radiation. Typically, treatment is delivered five days a week over several weeks.

When designing your treatment plan, your medical team relies on one or more types of 3-D scans of your body. These can include a CT scan, an MRI, and/or a PET scan. By looking at these scans and other test results, the radiation oncologist and his or her treatment team determine which treatment technique is best suited for your particular case.

Meet Your Treatment Team

Radiotherapy is administered to you by a team of highly qualified healthcare professionals, comprised of specialists that among them have years of experience in treating cancer. Some of the typical members of the team are listed below; depending on your treatment needs, other specialists may be asked to join the team.

The Radiation oncologist is your doctor throughout this process — a medical doctor who specializes in the use of radiation for treating cancer. The radiation oncologist will prescribe, plan and direct your treatment and is responsible for deciding what method of radiation therapy is best for your case.

The Medical physicist works with the Dosimetrist and the radiation oncologist to measure the precision of your treatment plan, and works with the equipment to calculate the best angles to treat your tumor, or tumor site. The medical physicist also runs frequent safety checks and makes sure that the equipment is working properly.

The Dosimetrist works closely with the radiation oncologist and the medical physicist to design your treatment. The dosimetrist determines the best angles from which to deliver the radiation, prescribes the length of time for each pulse of radiation, and develops strategies on how best to avoid giving radiation to healthy tissue in your body.

The Radiation therapist will conduct your treatment each session. He or she will position you on the treatment table, run the equipment, and work very closely with the medical physicist during your treatment.

The Radiation nurse coordinates your care, helps you learn about treatment, and tells you how to manage any side effects that you might experience.

What to expect during Treatment?

Step 1: The Consultation

First, you'll meet with your doctor, a radiation oncologist, to discuss your treatment. Based on your specific case, your radiation oncologist will tell you what type of radiation therapy he or she recommends, whether it will be given alone or in conjunction with other treatment methods, what the specific goals of treatment are, and what side effects you may experience. You can talk to your radiation oncologist about your treatment options and make a decision together. The consultation is an excellent opportunity for you to ask your radiation oncologist whatever questions you may have. Click here for a list of common questions.

Step 2: Imaging

In order for the radiation oncologist to design your treatment, the exact size and location of the tumor must first be determined. This is usually done by creating a detailed 3-D image of the tumor with a CT scan. Depending on the general location of the tumor, disease type and other factors, additional scans may be taken, which could include an MRI, a PET scan or an ultrasound scan. Your oncologist can rotate the image on his computer screen to view the tumor from every angle.

It is very important that the position in which you are scanned is reproduced at the time of treatment. Sometimes temporary skin marks and even tiny tattoos (about the size of a freckle) are made on your body to help the radiation therapist (RT) position you correctly each day for treatment. Depending on the location of the tumor, a body mold, head mask or other device may be constructed to make it easier for you to remain in the same position during treatment.

Step 3: Treatment Planning

Once your scans have been completed, your doctor, the medical physicist and the dosimetrist will meet to design your treatment plan. They take many factors into account when they design the treatment plan. These can include the type of cancer, its location and size, your medical history, and your lab test results. Based on these factors, the treatment plan specifies the amount of radiation to be delivered, the appropriate angles from which to deliver it, and the number of sessions needed to deliver the prescribed treatment.

Step 4: Getting Positioned for Treatment

Before each day's treatment, you may be asked to change into a gown. The radiation therapist (RT) will help you get positioned on the treatment "couch" — a platform designed to work with the radiation machine. If a facemask, mold or other device was created for you during the imaging process, it will be placed on you or under you at this time. The couch will be adjusted so a laser light shines on the mark that was put on your skin, helping to position you correctly. Depending on the type of machine you’re treated on, your treatment team may take a scan immediately prior to treatment, while you are on the couch. The purpose of this new scan is to show if the tumor has changed in size or position since the first one was created during imaging. If it reveals any changes, the RT will make the necessary adjustments to the position of the couch to ensure that you are properly aligned for treatment.

Step 5: Treatment Begins

The radiation is delivered by a machine called a linear accelerator, or linac. Most linacs have a gantry, which is the head of the machine. The gantry houses a device called a multi-leaf collimator that "shapes" the radiation beam so it conforms to the shape of the tumor from any given angle. During your treatment, the gantry will move around you to deliver the radiation. The radiation beam is not visible to the eye, so you will not see it when it leaves the gantry.

Your first two treatments may take 15 minutes or more, as your radiation therapist helps you get into position and takes images to verify that your setup on the machine is the same as the treatment plan. Subsequent treatments, however, are often shorter. In fact, some treatments — from entering the waiting room to leaving the clinic — can take as little as 12 to 30 minutes.

Step 6: Post-Treatment and Follow-Ups

You may experience some side effects from radiotherapy. If you do, they might not begin until after several sessions because the effects of radiation treatment are cumulative. Talk to your oncologist before and during treatment if you have any questions or experience discomfort. Click here to learn more about possible side effects.

After your treatment has ended, your radiation oncologist will recommend a schedule for periodic checkups to monitor the results. Typically, the first checkup is given in one to three months, and subsequent checkups are scheduled at six-month intervals, but yours may be more or less frequent, depending upon your situation. If symptoms or clinical circumstances suggest a recurrence, diagnostic tests such as blood tests, ultrasound scans, CT scans, MRIs, chest x-rays (CXR), or bone scans may be needed.

What you should ask your Doctor Radiation Oncologist?

This suggested list of recommended questions is only a guide and you will likely have other questions that you will want to ask your doctor.

Disease and Treatment

What type of tumor do I have? Is it benign or malignant?

What stage is my cancer?

What are my treatment options?

Why is radiation used to treat my type of cancer? Would radiosurgery be appropriate for my cancer?

How many sessions of treatment will I need?

If radiation therapy or radiosurgery is appropriate for me, what are the most frequent and most serious side effects I can expect? How long will side effects last? Is there anything we can do to reduce the chances of experiencing side effects or reducing their severity?

When will treatment start? How long is each treatment? When will it end? How often will I have treatments? How long will each treatment last?

What will happen if I don't have treatment?

Will I also need other treatments, such as chemotherapy, surgery, or hormone therapy? If so, when will I receive them, and in what order?

Will the treatment hurt?

Quality of Life

Will I be able to continue my normal activities during treatment? If not, how soon after treatment will I be able to resume them? Work? Sexual activity? Aerobic exercise?

What is the chance that the cancer will spread if I do not have treatment?

How will I feel during treatment? Will I be able to drive myself to and from treatment?

What can I do to take care of myself before, during, and after treatment?

Will radiation therapy affect my sex life or my ability to have children?

Will I need a special diet during or after my treatment?

Is it safe to take vitamins during treatment? Are there special lotions or deodorants that I should or shouldn't use?

Will I be able to drive myself to and from treatment?

Prognosis and Survival

What is the goal of treatment?

What is the prognosis (probable outcome) for people with this stage of cancer?

What is the probability that radiation therapy will work for me? It if works, what are the chances that the cancer will come back?

How will we know the treatment is working?

What are survival rates for my type and stage of cancer? After my treatment is completed, how often will I need to return for check-ups?

Questions about your Team and Treatment Facility

How many patients have you treated with my specific form of cancer?

Does this facility offer all of the treatment methods that will be used in fighting my cancer, or will I have to go to multiple treatment facilities?

Does this facility offer any support groups I can turn to during and after treatment?

Is there a dietician I can work with?

What other services are available to help me and my family deal with this disease?

What are reasons I should call you at night or on a weekend? Whom do I call and at what phone number?


There are two broad categories of radiation therapy; both are designed to target the tumor precisely while minimizing exposure to the surrounding, healthy tissue. In the first category, external beam radiation therapy (EBRT), the radiation is usually delivered by a machine called a linear accelerator, or linac, which focuses a high-energy x-ray beam into your tumor site from outside your body. In the second treatment category, the radiation is delivered by radioactive material placed inside the body near the cancer cells — a procedure called Brachytherapy (also called internal radiation therapy or implant radiation therapy).