What Is Stereotactic Body Radiotherapy?

What to Expect When Undergoing This Procedure

Stereotactic body radiotherapy (SBRT) is a type of radiation therapy that uses special equipment to precisely deliver a dose of radiation to a tumor. The aim of SBRT is to employ the highest possible dose of radiation to kill the cancer while minimizing damage to surrounding tissues and organs. SBRT is used to treat both non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) and even certain types of cancer that have spread (metastasized) to the lungs or other parts of the body.

Man using Stereotactic Body Radiation Therapy (SBRT)
Michael Goodyear / Wikimedia Commons 

Purpose of Procedure

SBRT uses several beams of high-dose radiation delivered at different angles with the aim of completely eradicating the targeted tumor. The best candidates for SBRT are people with well-defined, small tumors who cannot tolerate conventional surgery.

SBRT is mainly used to treat small primary (original) tumors but is increasingly considered for people with oligometastases (a small number of metastatic tumors).

Primary Tumor

SBRT is typically used for early-stage lung cancers in people who are unable to have surgery. A tumor may be considered inoperable due to its location or certain health conditions that could make lung cancer surgery risky, including older age.

SBRT can even replace surgery for people with inoperable stage 1 lung cancer, often with the same efficacy and long-term survival rates as traditional surgery.

For SBRT to be effective, tumors need to be small, usually less than 5 centimeters (2 to 3 inches) in diameter, and not be situated too close to the airways, heart, or other critical structures.

According to a 2019 study in Lancet Oncology, SBRT nearly doubles survival in people with stage 1 lung cancer when compared with standard radiation therapy.

Oligometastases

Oligometastases is defined as a limited spread of cancer for which local ablative therapy could be curative. Conceptually, the purpose of local treatment is to cure the malignancy and ensure disease-free survival.

Although this is not always possible, SBRT is an option that oncologists will consider if one or a few small metastatic tumors are found in the lungs (but generally no more than five). These metastases may originate from the primary tumor in the lung or a primary tumor in another part of the body.

Alternatively, SBRT may be used to treat oligometastases in other parts of the body that have spread from the lungs (most commonly in the liver, brain, and adrenal glands) or from other primary tumors in the body.

A 2010 study from the University of Pittsburgh involving people with metastases from different types of cancer, including lung cancer, found that SBRT increased survival without reducing the quality of life.

Risks and Contraindications

When considering whether SBRT is an appropriate treatment option, doctors will look at both the size and location of the tumor.

There are no absolutes when assessing who is or is not a candidate for SBRT, but there are some factors that can potentially contraindicate treatment:

  • Tumor size: Most radiation oncologists will not perform SBRT on tumors larger than 6 cm (just over 2¼ inches) in diameter. It can be done, but the chances for controlling a tumor decreases the larger a tumor is.
  • Tumor location: Surgeons are often a little reluctant to perform SBRT on tumors located in the central part of the lung but will generally do so for tumors up to 4 cm (1½ inches) in diameter that are at least 2 cm (¾ inch) from a major airway. SBRT is typically contraindicated when a tumor is located near the hilus (the junction between the lungs where the bronchi, arteries, veins, and nerves enter and exit the lungs).
  • Adjacent organs: SBRT is also typically avoided if it can cause harm to any organ or structure critical to the body's function. This includes the heart, major vessels, spinal cord, brachial plexus, phrenic nerve, and recurrent laryngeal nerve. SBRT should only be considered if these structures are at least 2 cm away from the tumor.

People with tumors in the central portion of the lung are at greater risk of radiation toxicity and side effects than those with peripheral tumors, such as lung adenocarcinomas.

The same is true for people with severe interstitial lung disease (ILD) in which permanent scarring of the lungs occurs as a result of smoking, chemical exposure, autoimmune diseases (like rheumatoid arthritis, scleroderma, lupus, or sarcoidosis), or genetic disorders (like Gaucher disease). Although ILD does not contraindicate SBRT outright, the benefits of treatment need to carefully weighed against the risk of further lung injury.

Before the Procedure

Before SBRT can be performed, you will undergo a series of imaging tests to locate the tumor and map the exact area to be treated. This may involve a magnetic resonance imaging (MRI) or computed tomography (CT) scan, as well as a technique called four-dimensional imaging that maps the target area as it moves during inhalations and exhalations. This is usually done over one or more sessions in advance of the scheduled procedure.

A mold will also be made of your upper body, which you will lay on the day of your treatment so that you can remain in place and still during the procedure. To make the mold, you are placed in the desired position on a large plastic bag filled with a quick-setting, plaster-like material.

Permanent tattoo marks about the size of a pin will also be placed on the skin to ensure the SBRT beams are properly directed in three dimensions. These can be removed at a later date with laser skin treatments if desired.

Once the coordinates are mapped and the radiation dose is calculated, SBRT can proceed as scheduled. In some cases, SBRT and the set-up for it can be done on the same day (typically if only a single session is required). Other times, set-ups are scheduled a week or two in advance.

Timing

Depending on the location and size of the targeted tumor, each SBRT session can take anywhere from 20 to 60 minutes. Some people may only require one session; others may require up to eight sessions given over consecutive days.

With the set-up time and pre-treatment tests, you should expect to spend no less than two to three hours in the facility. Some busier units may take longer.

Location

SBRT can be performed in the radiology unit of a hospital or in a specialized radiology clinic. SBRT is performed in a dedicated room using a linear accelerator.

This is a sophisticated piece of technology comprised of a movable flatbed that you lie down on and a large rotating gantry that can be moved around the body to deliver radiation at different angles. Some newer models are equipped with a robotic arm.

What to Wear

Wear loose-fitting clothes that you can easily take off and put back on as you may be asked to change into a hospital gown. Leave any jewelry at home.

You can leave your shoes, socks, and underpants during the procedure, but bras need to be removed.

Tell your doctor in advance if you have any implanted medical devices, such as a pacemaker, artificial heart valve, stent, aneurysm clip, cochlear implant, or neurostimulator.

Food and Drink

You will typically be asked to stop eating, drinking, or taking anything by mouth after midnight on the day of the procedure.

If you take chronic medications, let your doctor know. In some cases, you may be allowed to take them with a little sip of water. In others, you may be asked to wait until after the procedure to take them.

Cost and Insurance

The cost of SBRT can vary by your location and the facility used, with the median costs hovering around $27,145 in 2016. While that is around half the cost of wedge resection surgery, it is still an expensive procedure requiring prior authorization from your health insurer.

To estimate out-of-pocket expenses for the procedure, check your policy for the copay/coinsurance costs before and after your deductible is met. Most insurance policies will cover a portion of the cost. If you meet your annual out-of-pocket maximum, the entire cost of the procedure may be covered.

Always ensure that the radiology unit and staff are in-network providers. If they aren't, ask your oncologist if there are in-network providers you can use. Out-of-network providers will almost invariably cost you more.

What to Bring

There is usually nothing you need to bring to an SBRT session outside of your driver's license (or other official forms of ID), insurance card, and an approved method of payment if needed.

If you wear contact lenses the day of the procedure, you will be asked to remove them, so you should bring glasses and a lens case/solution. Likewise, dentures must also be removed, so bring a case for them if you wear them.

You can bring a blanket and slippers to cover your legs and feet if you tend to get cold, but most radiology units have blankets and slippers on-hand if you ask.

Other Considerations

Most radiology units advise against driving yourself home after an SBRT. To be safe, ask a friend or family member to drive you to and from your appointment or organize transport with a local service.

During the Procedure

SBRT is overseen by a radiation oncologist who conducts the initial set-up and dosing instructions. Pre-tests scans are reviewed either by the radiation oncologist or an on-site radiologist. The session itself is performed by a highly trained radiation therapist with the assistance of a radiation nurse.

On the day of the SBRT, plan to arrive at least 30 minutes beforehand to check-in, fill out medical information forms, and provide payment if needed. You will also be asked to sign a liability form stating that you understand the procedure you are undergoing along with its possible risks.

Once you are checked in, a nurse will lead you to the back to undress and lock up any of your valuables.

Pre-Procedure

After you have changed, you will be led to the procedure room where the nurse will check your weight and vital signs (blood pressure, pulse, and temperature). They will also check that you adhered to the recommended food and drug restrictions.

You will then be escorted to a separate room to undergo a low-dose CT scan. This is done before each session to make sure that your position and the area being treated are correct.

The nurse will then take you to the procedure room where SBRT is performed. Even though the linear accelerator is a relatively open device, some people still experience claustrophobia when lying still for a long period of time.

If you feel claustrophobic or have a queasy stomach prior to SBRT, let the nurse know when you arrive. You may be offered anti-anxiety or anti-nausea medications to help ease your symptoms. Also inform the nurse about any pain you're currently dealing with (e.g., back, neck) so they are aware of the potential of you needing a break during treatment.

Once you are settled, you will be led to the flatbed of the linear accelerator and asked to lie down on the pre-cast body mold. In most cases, your arms will be folded behind your head. Your gown may be opened to reveal the tattoo marks. Pillows and bolsters may be used to keep you comfortable and in the correct position.

Throughout the Procedure

The procedure requires you to lie completely still for protracted periods of time. At times, you will be asked to hold your breath. The movement of the gantry is computerized with preset coordinates but overseen by the therapist, who will monitor the procedure from behind a radiation screen and communicate with you via an intercom.

Once the procedure begins, you will not feel anything. The experience is not unlike that of an X-ray, although there will be whirring and clunking sounds as the gantry moves around the body to deliver radiation.

If you need a break due to discomfort or for some other reason, tell the therapist. However, do not move until the therapist turns off the machine and tells you that it's OK to do so.

Once the session is complete, you will be led back to the changing room to change into your clothes.

Post-Procedure

Most radiology units will ask you to stay for 30 minutes to an hour after SBRT to ensure that you don't experience any unexpected side effects.

If you've delayed a dose of chronic medication due to your doctor's instructions, you can take it once the procedure is completed.

After the Procedure

You will be asked to take it easy for the rest of the day and likely a day or two after. You should eat as soon as you can. Depending on the side effects experienced, you may be able to return to normal activity in a day or so.

The risk of side effects from SBRT are closely linked to the total amount of radiation received. Still, because the area of treatment exposure is relatively small, around 50% of people who undergo SBRT experience no side effects at all.

The most common short-term side effects associated with SBRT include:

  • Fatigue, often lasting the first few days after treatment
  • Nausea or vomiting, which can usually be treated with an over-the-counter anti-nausea drug or a prescription one like Zofran (ondansetron)
  • Swelling at the radiation site, which can usually be treated with over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs).

Although complications are rare, call your doctor if symptoms persist or worsen or you experience lymphedema, the abnormal swelling of the arms, legs, or other parts of the body.

On rare occasions, people may experience radiation side effects months or years later, largely depending on the extent of the treatment area. These may include:

  • Chronic arm or shoulder pain caused by damage to the brachial plexus
  • Pulmonary fibrosis, areas of lung scarring that can decrease lung function and lead to shortness of breath
  • Weakened bones, increasing the risk of accidental fracture
  • Secondary cancers, such as esophageal cancer

Interpreting Results

The tumor will gradually shrink over the course of months after SBRT. During this time, follow-up exams will be given to assess the tumor size and the overall effectiveness of the treatment. The American Association for Thoracic Surgery currently recommends undergoing low-dose CT scans every six months for the first four years.

If there are no signs of cancer on a CT scan, a positron emission tomography (PET) scan may also be ordered, which can detect changes in metabolic activity consistent with cancer. If no such changes are found after that, the doctor may declare that you are in remission, meaning that all tests, physical exams, and scans show no clinical signs of cancer.

Even so, you will be advised to continue seeing your oncologist for regular follow-ups every six to 12 months.

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