External Beam Radiation Therapy (EBRT)

Overview

External Beam Radiation Therapy (EBRT) is the most commonly used form of radiation therapy for cancer treatment. In this procedure, patients lie on a treatment table while a machine carefully directs radiation beams toward the tumor. The machine does not make contact with the patient; instead, the radiation oncology team adjusts it to deliver targeted radiation to the cancer cells from a safe distance, effectively destroying them.

The primary aim of EBRT is to eradicate cancer cells and decrease tumor size while minimizing damage to the surrounding healthy tissue.

Types of energy used in external beam radiation therapy

Radiation therapy uses energy beams composed of highly charged particles capable of destroying cancer cells. The strength of these particles allows them to penetrate deep into tissues, affecting both cancerous and healthy cells depending on the specific type of radiation treatment administered.

A primary objective of EBRT is to eliminate cancer cells while sparing healthy cells from damage.

These highly charged particles include:

• Photons (X-rays and gamma rays): Photons are fundamental units of energy capable of penetrating deeply into tissue to destroy cancer cells. They are the primary type of radiation used in most EBRT treatments.
• Protons: Protons are positively charged particles utilized in a newer form of EBRT known as proton therapy. This method delivers a concentrated burst of radiation to tumor cells, stopping short of affecting healthy cells. Proton therapy may offer better protection for healthy tissue, but it is not yet widely available. Ongoing research is focused on understanding the biological interactions of protons with cells and comparing the benefits of proton therapy to traditional photon-based EBRT.
• Electrons: Electrons are negatively charged particles that do not penetrate as deeply as photons or protons. Consequently, electron beams are primarily used to treat skin cancer or tumors located close to the surface.

A Linear Accelerator (LINAC) device is used in the majority of forms of external beam radiation therapy to accelerate particles and direct them toward cancer cells. An apparatus known as a particle accelerator is used in proton treatment.

Types of external beam radiation therapy

Advanced technology is used in EBRT to deliver radiation beams to your tumor. In order to give your body time to recover between sessions, treatments are typically spaced out across a few days.

• 3D Conformal Radiation Therapy: This technique directs multiple energy beams to conform precisely to the tumor’s size and shape. Using computer software, your care team analyzes body images, often from CT scans, and may include PET or MRI scans. These images reveal the tumor’s size, shape, and location. A computer creates a 3D model of the tumor relative to surrounding healthy tissue. The radiation oncology team then designs the energy beams to target the cancer cells accurately.
• Intensity-Modulated Radiation Therapy (IMRT): An advanced form of 3D conformal radiation therapy, IMRT adjusts the intensity of multiple small beams within each main beam. This allows for higher doses of radiation to be focused on the cancer cells while minimizing exposure to healthy tissue.
• Image-Guided Radiation Therapy (IGRT): This method uses imaging during each treatment session to ensure precise delivery of radiation beams. While 3D conformal radiation therapy and IMRT use initial imaging and computer software to customize energy beams, IGRT updates imaging and analysis during every session. On-board CT scans are commonly used to track and adjust the energy beams based on tumor changes, potentially leading to dose adjustments or beam redesigns (adaptive radiation therapy).
• Tomotherapy/Helical Tomotherapy: Radiation is delivered in a spiral pattern while you lie on a table. You move through a donut-shaped machine that encircles you, directing energy beams of varying intensity to the tumor.
• Stereotactic Radiosurgery (Gamma Knife Surgery): High doses of radiation are directed at small brain tumors, providing a precise treatment option for brain tumors that are not safely removable by surgery. Despite the name, this procedure does not involve cutting but is called “surgery” due to its precision.
• Stereotactic Body Radiation Therapy (SBRT): Similar to stereotactic radiosurgery, SBRT targets tumors outside the brain, such as those in the liver, lung, or spine. It is often used when surgery poses high risks due to the tumor’s location or the patient’s health.
• Intraoperative Radiation Therapy (IORT): Administered during surgery when parts of a tumor cannot be safely removed. The surgeon shields healthy tissue while a machine delivers radiation directly to the cancer site, with the patient under anesthesia.

Reasons for undergoing the procedure

Tumors shrink and cancer cells are killed with EBRT. It could be applied to:

• Destroy Cancer Cells or Prevent Their Spread: EBRT is a primary treatment option for many types of cancer, aimed at eliminating cancer cells and inhibiting their spread.
• Complement Other Cancer Treatments: EBRT can be combined with other treatments such as surgery, chemotherapy, or immunotherapy. It is often used to shrink tumors before surgery (neo-adjuvant therapy) and to destroy any remaining cancer cells after surgery to prevent recurrence (adjuvant therapy).
• Relieve Symptoms: EBRT is frequently used in palliative care to help manage pain and other symptoms in people with chronic or long-term conditions. It can shrink tumors that cause discomfort or other issues, improving the patient’s quality of life.

Conditions treated

For the majority of localized cancer forms, external beam radiation therapy is the preferred method of radiation therapy. “Local” refers to the isolation of cancer cells within a particular body region. Many of the most prevalent forms of cancer are treated using EBRT, including:

• Leukemia.
• Lung cancer.
• Breast cancer.
• Colon cancer.
• Non-Hodgkin lymphoma.
• Prostate cancer.
• Uterine cancer.
• Head and neck cancer.
• Colon cancer.
• Others cancers

Risks

While your doctor will do their best to minimize damage to healthy cells, complete prevention of side effects is nearly impossible. Healthy cell destruction can lead to various adverse reactions. Fatigue is the most common side effect of radiation therapy. Depending on the area being treated, you may also experience:

• Hair loss
• Headaches
• Loss of appetite
• Difficulty swallowing
• Shortness of breath
• Nausea and vomiting
• Urinary issues, such as incontinence
• Skin irritation, including redness and discomfort
• Soreness and inflammation at the treatment site

Your experience with EBRT will be unique, even if you have the same type of cancer as another patient undergoing the same treatment. While your care team works diligently to protect healthy cells, some side effects may still occur.

Before the procedure

EBRT is the preferred radiation treatment for most localized cancers, where the cancer cells are confined to a specific area of the body. EBRT is effective in treating many common types of cancer.

In the course of simulation:

• Positioning: You will be placed in the same position as you will be during treatment.
• Imaging: A Computed Tomography (CT) scan, Magnetic Resonance Imaging (MRI), or Positron Emission Tomography (PET) scan will be performed to capture images of your tumor. These images help your radiation oncology team precisely locate the cancer site, or treatment field, and design the energy beams to target the cancer cells.
• Marking: Small, freckle-sized marks will be placed on your skin to indicate the treatment field. These marks ensure consistent radiation delivery during each session and should remain throughout the treatment period.
• Fitting for Accessories: You may be fitted with accessories, such as a mask or cast, to help maintain the correct position during treatment.
• Treatment Planning: Using the information gathered from the simulation, your radiation oncology team will design your treatment plan over the next few days or weeks.

Treatment sessions typically last less than simulation sessions. To create an efficient EBRT, gathering information early on is crucial. A simulation can last for two hours or as little as thirty minutes.

During the procedure

After receiving care in a hospital or treatment facility, you will depart the same day. While receiving treatment:

• Your position will be the same as it was during the simulation. Your radiation therapist will assist with applying any restraint devices, such as a cast or mask.
• Your radiation therapist will leave the room after you’re in position so they can run the machine. Throughout therapy, they’ll be able to keep an eye on you via a monitor. An intercom will be available for you to communicate with your therapist.
• The machine is controlled remotely by the therapist, who will move it around you and produce little noises while you receive treatment. The energy beams are positioned by the machine’s movements at the exact spots required to kill cancer cells. You must remain still while the treatment is being performed. 
• Throughout your session, the equipment won’t emit radiation continuously, allowing you to breathe normally. Rather, each time its position changes, it will emit radiation for up to several minutes.

Treatment sessions typically last between 15 and 30 minutes, with the majority of the time dedicated to proper positioning. The therapist will inform you when the radiation begins.

Most EBRT cancer treatments are administered daily, Monday through Friday, over a period of two to eight weeks. This schedule allows healthy cells time to recover, reducing side effects.

However, there are exceptions. For instance, stereotactic radiosurgery often involves a single high-dose treatment session.

After the procedure

Following therapy, you will be allowed to leave the hospital or treatment center. Depending on your state of mind, you might be able to get back to your regular schedule right away.

Outcome

Responses to treatment can vary significantly from person to person. Some individuals may be able to return to their daily routines shortly after radiation therapy sessions, while others might experience considerable fatigue that necessitates time off work for recovery.

Side effects often become more pronounced as treatment continues, as radiation therapy does not kill cancer cells immediately. It typically takes days or weeks of treatment for the accumulated damage to result in cell death. Initially feeling well may lead to increased recovery time once the effects of cell damage set in.

Similarly, side effects can differ after treatment concludes. It may take a few weeks to feel fully recovered, or it might take several months before returning to normal activities.