What is external beam radiation therapy

External beam radiation therapy (EBRT) is the most common type of radiation therapy. It directs high-energy radiation beams at the cancer.

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How EBRT works

EBRT is delivered using a radiation machine. The most common type is a linear accelerator (see below).

You will lie on a treatment table or “couch” under the machine. The machine does not touch you, but it may rotate around you to deliver radiation to the area with cancer from different directions. This allows the radiation to be more precisely targeted at the cancer and limits the radiation given to surrounding normal tissues.

Linear accelerator

This is a general illustration of a linear accelerator (LINAC). It’s large and often kept in a separate room. A CT scan machine is usually attached to the linear accelerator. The machine used for your treatment may look different. There may also be imaging devices on or near the linear accelerator, which help position you accurately on the couch

The treatment course

After the planning session, your radiation oncologist will work out the total dose of radiation needed to treat the cancer and the total number of treatments.

Fractions – In most cases, the total dose will be divided into a number of smaller doses called fractions, which are given on different days. The length of each session will depend on the type of EBRT.

Course – A course of treatment refers to the total number of sessions of radiation therapy. How often and how long you need to have radiation therapy depends on the type of cancer, the total dose required, the location of the cancer and the aim of treatment.

In general, higher total doses of radiation are used for curative treatment. A fraction of the dose will be given once a day, Monday to Friday, for 3–8 weeks. Dividing the total dose into separate treatment sessions with weekend rest breaks allows the healthy cells time to recover. Occasionally, the radiation oncologist may recommend two treatments a day, with usually six hours between the sessions.

A course of radiation therapy used to relieve symptoms (palliative treatment) is usually shorter. You may have 1–15 sessions. Palliative radiation therapy may not be given every day.

Each fraction of radiation causes a little more damage to cancer cells, so it’s important to go to all of your scheduled sessions if your treatment is curative. When you miss sessions, cancer cells have more time to repair the damage, so your radiation therapy may not work as well. If a treatment break is necessary, you may have extra sessions to make up for the missed sessions.

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Home » Radiation Therapy » External Beam Radiation Therapy (EBRT)

External Beam Radiation Therapy (EBRT) refers to the delivery of tightly targeted radiation beams from outside the body. A course of EBRT involves several daily treatments (fractions) over a few days to a few weeks. The radiation oncology team controls the radiation machine (usually a linear accelerator) to generate and direct the radiation beams. EBRT usually delivers X-rays (also called photons) but can also use electrons or other rarer particles such as protons. These have different properties which can be useful for different cancers or settings. The experience for the patient is similar to having an X-ray or CT scan – there is no sensation of being treated.

Conventional external beam radiation therapy (EBRT)

EBRT involves targeted radiation beams being delivered from outside the body. It is a non-invasive method of delivering radiation to a tumour. The radiation beams are shaped as they come out of the linear accelerator and/or before they reach the patient to make sure that they are carefully directed at the cancer.

Intensity-modulated radiation therapy (IMRT)

IMRT is a special form of EBRT involving the delivery of hundreds of small radiation beams with different intensities, entering the body from a number of different angles. This form of radiation therapy was first commonly used for prostate and head and neck cancers in Australia, but is now being used for many cancer sites. It is very precise, sometimes allowing higher doses to be given safely, without causing damage to the surrounding organs.

Image-guided radiation therapy (IGRT)

IGRT involves repeated imaging of the tumour during treatment. It is used in nearly all IMRT treatments to ensure accuracy to the millimetre. IGRT allows the treatment team to see small changes in tumour or organ shape, size and position, enabling the treatment team to make necessary adjustments to the radiation delivery during or between daily treatments. This ensures that the cancer cells remain targeted while reducing radiation exposure to healthy cells.

Stereotactic radiosurgery (SRS)

SRS is used to treat small tumours with well-defined edges. It is particularly useful for cancers in the brain or spine. In SRS treatments, a single high dose of radiation is delivered to the tumour with the assistance of highly accurate imaging and planning. A head frame is usually required for brain treatments to ensure the patient stays completely still.

Stereotactic body radiation therapy (SBRT)

SBRT delivers very high dose radiation focally to small tumours outside of the spine or brain. Immobilisation of the body is critical, although small movements that may affect the precise delivery of the treatment, such as breathing, are taken into account. For this reason, SBRT is usually given in several slightly lower dose treatments than SRS, across several sessions. Stereotactic radiation therapy may also be used for tumours in the brain or spinal cord, similar to SRS, but again using a few lower dose treatments rather than the one larger dose. This approach to treatment is still partially in a research phase but it is likely to become a bigger part of radiation oncology in the future.

Proton therapy

Particle therapy is an advanced form of radiation therapy that can be advantageous in specific cases. The most common form is called proton therapy and at this stage, Australian patients must travel overseas to access this treatment. Individuals who are most likely to benefit from proton therapy include those who have tumours that are near vital organs (such as base of skull tumours adjacent to the brainstem and nerves responsible for vision) and young patients where long term effects of treatment can potentially be minimised (such as hormonal imbalances, intellectual development delay and secondary cancers).

Useful Resources

The ‘Patient Pathway’ video below outlines the pathway that a patient will go through when being treated using radiation therapy (also called radiotherapy). This video shows the roles of each of the specialties in the radiation oncology team including radiation oncologists, radiation therapists and radiation oncology medical physicists.

Patient undergoing radiation therapy.

External beam therapy (EBT) is a method for delivering high-energy x-ray or electron beams to a patient's tumor. Beams are usually generated by a linear accelerator and targeted to destroy cancer cells while sparing surrounding normal tissues. EBT also may be used to relieve symptoms in patients with advanced cancer or cancer that has metastasized.

To prepare for EBT, your doctor will perform a physical exam and use CT scanning to conduct a treatment simulation session. Other imaging procedures may be used to help determine the exact shape and location of your tumor, and a special device may be created to help you maintain the same exact position during each treatment. Your doctor will give you specific instructions based on the treatment technique to be used.

External beam therapy (EBT), also called external radiation therapy, is a method for delivering a beam or several beams of high-energy x-rays to a patient's tumor. Beams are generated outside the patient (usually by a linear accelerator, see below) and are targeted at the tumor site. These high energy x-rays can deposit their dose to the area of the tumor to destroy the cancer cells and, with careful treatment planning, spare the surrounding normal tissues. No radioactive sources are placed inside the patient's body.

External beam therapy is used to treat the following diseases as well as many others:

Why is this procedure performed?

External beam therapy is most commonly used to treat cancer. Often, the goal is to eliminate a tumor or prevent a tumor from returning. The procedure may also be performed before or after surgery to remove a cancerous tumor, to reduce the tumor size before surgery, or to prevent the tumor from coming back after surgery.

EBT may also be used as a palliative treatment in patients with advanced stage cancer or cancer that has metastasized. In this case, the goal of therapy is to reduce a patient's symptoms rather than cure the cancer.

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Delivery of external beam therapy requires a treatment team, including a radiation oncologist, medical physicist, dosimetrist and radiation therapist. The radiation oncologist is a physician who evaluates the patient and determines the appropriate therapy or combination of therapies. He or she determines what area to treat and what dose to deliver. Together with the medical physicist and the dosimetrist, the radiation oncologist determines what techniques to use to deliver the prescribed dose. The physicist and the dosimetrist then make detailed treatment calculations and quality assurance checks prior to treatment delivery. The radiation therapists are specially trained technologists who deliver the daily treatments.

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Radiation oncologists use linear accelerators or cobalt machines to deliver external beam therapy. Your radiation oncologist will determine the equipment most suited to your treatment. The linear accelerator is the most commonly used device for external beam therapy.

• Linear Accelerator - see linear accelerator page

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The equipment is operated by a radiation therapist, a highly trained technologist. The overall treatment plan is created by the radiation oncologist, a highly trained physician specializing in treating cancer with radiotherapy.

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The process of external beam therapy involves three parts:

• Simulation
• Treatment Planning
• Treatment Delivery

The goal of simulation is to determine the treatment position that will be used daily, to make devices that will help the patient maintain that position, and to obtain the necessary images for treatment planning. The radiation therapist places the patient in the treatment position on a CT scanner. Masks, pads or other immobilization devices are typically used to help the patient to hold still and in a specific position during the simulation. These devices will be used for the treatment to achieve the same position daily, so it is important that the patient can maintain that position. Images of the treatment area are taken in the treatment position. The radiation therapist places small marks on the patients to help guide the daily treatments. These marks may be tattoos or colored ink. The tattoos will be permanent, but the colored ink will eventually fade. Marker seeds may be placed in the target tumor or organ at simulation or during a separate surgical procedure. These seeds or markings are intended to help the radiation therapist position the patient during each treatment session.

For treatment planning, the dosimetrist, medical physicist and radiation oncologist use a special computer program to calculate the radiation dose that will be delivered to the patient's tumor and the surrounding normal tissue. The radiation oncologist will determine the volume of the tumor and other areas that need to be treated and outline those on the treatment planning images. He or she will also outline normal structures that should be avoided or considered in devising the treatment plan. Together, the oncologist, dosimetrist and physicist will generate a treatment plan that delivers the appropriate dose to the tumor while minimizing dose to surrounding normal tissues. In certain cases, this process may employ such techniques as three-dimensional conformal therapy, intensity-modulated radiation therapy (IMRT), or volumetric modulated arc therapy (VMAT). This planning is based on CT, MRI and PET/CT scans which may be done in the radiology department or the radiation oncology department.

After the simulation and planning have been completed, the treatment can begin.

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Before each treatment session, the patient may be asked to change into a gown. The radiation therapist brings the patient into the treatment room and places him/her on the treatment couch of the linear accelerator in exactly the same position that was used for simulation using the same immobilization devices. The therapist carefully positions the patient using the alignment lasers and the marks that had been placed on the patient during simulation. Some form of imaging is often used prior to the treatment delivery to verify the accuracy of the patient setup. Some of the types of imaging that can be used include x-rays, ultrasound and cone beam CT. The therapist goes outside the room and turns on the linear accelerator from outside. Beams from one or more directions may be used and the beam may be on for as long as several minutes for each field.

The treatment process can take one hour or less each day and most of the time is often spent positioning and imaging the patient. The first treatment usually takes the longest; subsequent treatments take between 15 and 30 minutes. The actual treatment may last only several minutes. The duration of a patient's treatment depends on the method of treatment delivery, such as IMRT, and the dose given. The length of each treatment will usually be the same from day to day.

Patients usually receive radiation treatments once a day, five days a week for a total of two to nine weeks. The patient's diagnosis determines the total duration of treatment. Occasionally, treatments are given twice a day.

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External beam therapy is painless but patients will hear buzzing or clicking noises during treatment. The linear accelerator may rotate or move during treatment. Patients feel nothing out of the ordinary, but may sometimes smell an odd smell during treatment that is caused by the ozone produced by the linear accelerator. Some patients may also see a colored light when they receive their treatment; this event is especially true for patients having their brain or eye treated.

Your doctor may recommend a series of follow-up exams after treatment. These may include a physical check-up, imaging exam(s), and blood or other lab tests.

These visits help your doctor see if your condition is stable or has changed. They also allow you to discuss any treatment side effects with your doctor.

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Once treatment is complete, patients are asked to return for follow-up visits. During these appointments, patients will undergo evaluation, including imaging exams or blood tests, to determine if their cancer has been eliminated or if additional treatment is required. Even if the cancer has been cured, patients can expect to continue periodic visits to follow-up with their doctor.

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This page was reviewed on January, 31, 2019

For more information about this and other radiology procedures, please visit Radiologyinfo.org