Fiducial markers

This page was reviewed under our medical and editorial policy by

Bertram Yuh, MD, MISM, MSHCPM, Urologic Surgeon, City of Hope | Duarte

This page was reviewed on August 17, 2023.

Fiducial markers, also known as fiducials, are tiny metal implants (about 3 mm in size) that are placed in your body through a fine needle to guide radiation treatment. The markers themselves aren’t painful, and you aren’t able to feel them inside you.

Why are fiducial markers used?

Fiducials are most commonly used for prostate cancer patients undergoing external beam radiation therapy. However, they can also be used to guide treatment for other types found within soft tissue, including lung, head and neck cancers.

External radiation uses a machine that aims targeted radiation treatment precisely at the location of the tumor. Because radiation can cause side effects to normal, healthy cells, it’s important for your doctor to aim the radiation beams directly at the tumor.

To achieve this, fiducial markers are often used. Once in place, the seeds clearly show up in X-rays. Your care team will use the markers to know exactly where to aim the radiation. Since organs and tissue can move slightly in your body, fiducial markers make it easier for your radiation oncologist to administer accurate treatment every time.

Benefits of fiducial markers

Fiducial markers allow for more precise radiation treatment, which means the radiation is more likely to be successful at killing cancer cells and less likely to reach healthy cells, reducing side effects from the procedure.

How to prepare for your procedure

If you’re scheduled to have fiducial markers inserted before starting radiation, your care team will let you know exactly how to prepare.

Before your fiducial marker insertion:

  • Inform your care team about any allergies or medical conditions you have and all prescription and over-the-counter medicines and supplements you take. Due to the risks of radiation, be sure to tell your doctor if there’s a possibility that you’re pregnant.
  • Your care team may ask you to temporarily stop taking certain prescription and over-the-counter medications the week before the procedure, such as blood thinners, aspirin and ibuprofen.
  • You may be prescribed an antibiotic to take on the day of the procedure. This is intended to help lower your chance of infection.
  • You can go about your day normally and eat meals, because fasting isn’t required for this procedure. (For prostate treatment, you may need to do an enema at home the night before the procedure, but you can still eat normally.)
  • It’s a good idea to arrange for someone to take you home after the procedure.

What to expect

The fiducial marker insertion is usually done as an outpatient procedure, so you typically don’t need to stay in the hospital.

On the day of your fiducial marker insertion, you may be asked to first give a urine sample, since the procedure may need to be postponed if you have a urine infection. General anesthesia may be used in some cases, such as with children.

The procedure generally follows these steps:

  • You’re positioned on the table to allow your care team to access the area.
  • You’re connected to monitors—and to an intravenous (IV) line if sedation medication is required. Doctors typically use local anesthesia to numb the area where the fiducial markers are being inserted, so that you don’t feel discomfort.
  • Using a hollow needle inserted through the ultrasound probe, your doctor places about three fiducial markers at the site of the tumor. Computed tomography (CT) or ultrasound guidance helps the doctor know exactly where to put the needle.
  • Afterward, an X-ray is performed to check that the markers are positioned correctly.

The entire procedure should be finished in about one hour.

Following the procedure, you’ll be instructed to limit your activity for about 24 hours and stay hydrated. If you feel unwell, call your care team for guidance.


Generally, fiducial marker insertion is a safe and well-tolerated procedure, and it can help guide treatment to the appropriate location while preserving healthy cells. However, there’s always a chance of side effects with any medical procedure.

Risks associated with fiducial marker insertion include:

  • Markers that may move and shift
  • Infection at the incision site

Depending on where the markers are placed, site-specific complications may occur, such as:

  • Markers in the lung may create air pockets and cause a collapsed lung
  • Markers in the prostate may cause rectal bleeding, blood in urine, or discomfort or stinging when urinating

Always alert your doctor if you notice any of the following symptoms:

  • Fever
  • Pain that worsens
  • Chills or body shakes

After the procedure, it’s best to follow your care team’s instructions, which usually include avoiding heavy lifting for a few weeks. If you feel unwell at any point while you’re recovering, be sure to call your care team for guidance.

How will I know if my procedure was successful?

After an X-ray, your doctor should be able to determine that the markers were inserted correctly into the body. Once your first course of radiation is scheduled, the markers will be used by your radiation oncologist to plan your treatment.

If you have any questions or concerns about your upcoming radiation treatment or your fiducial markers, your care team is always there to help.

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