Rectal spacer gel and gold marker placement

A short procedure before prostate radiation. A soft gel is injected between the prostate and the rectum to move the rectum away from the radiation, and three tiny gold markers are placed in the prostate so the radiation can be aimed precisely each day.

Also called SpaceOAR, SpaceOAR Vue, Barrigel, Hydrogel spacer, Rectal spacer, Perirectal spacer, Prostate-rectum spacer, Fiducial markers

Where: Clinic procedure room or outpatient surgery center
Anesthesia: Local numbing, often with light sedation; sometimes general anesthesia
Time in the room: About 20 to 45 minutes
Hospital stay: Same day
Back to normal: 1 to 2 days
Back to work: Next day for most people

See the steps

ProstateRectumPerineumBladder

Where it happens. The highlighted part is what this procedure treats.

Overview

Radiation for prostate cancer has to pass close to the rectum, which sits right behind the prostate. A spacer is a soft gel injected into the thin space between the two. It pushes the rectum back by about 1 centimeter (a little less than half an inch), so the rectal wall receives less radiation.

The gel stays in place through the weeks of radiation, then the body slowly absorbs it over several months. The most widely used gel is made of polyethylene glycol and is known by the brand name SpaceOAR. Another, made of hyaluronic acid, is known as Barrigel. Both work the same basic way.

Fiducial markers are tiny gold seeds, smaller than a grain of rice, placed inside the prostate. The prostate shifts slightly from day to day as the bladder and bowel fill and empty. Before each treatment, the radiation team takes a quick image, finds the markers, and lines up the beam to within a few millimeters.

Both are usually placed in one visit, about 1 to 2 weeks before your radiation planning scan, with needles passed through the skin between the scrotum and the anus under ultrasound guidance. In a large randomized trial, the spacer lowered the radiation dose to the rectum and reduced bowel side effects over the following years.

The parts of your body involved

The back of the prostate rests against the front of the rectum, with only a thin layer of tissue and fat between them. That is why radiation aimed at the prostate also reaches part of the rectal wall. The gel fills and widens this thin space. Below both organs is the perineum, the skin between the scrotum and anus, where the needles enter.

Prostate
The gland being treated with radiation. The gold markers go inside it.
Rectum
The last part of the bowel, directly behind the prostate. It is the organ the spacer protects.
The space between
A thin layer of tissue and fat separating the prostate from the rectum. The gel is injected into this layer.
Perineum
The skin and muscle between the scrotum and the anus, where the needles go in.

Why it’s done

Both steps help the radiation do its job more safely: the markers make the aim more precise, and the spacer keeps more of the rectum out of the high-dose area.

Protecting the rectum
Moving the rectum away lowers its radiation dose, which reduces the chance of rectal bleeding, urgency and other bowel side effects in the years after radiation.
Precise daily aim
Gold markers show up clearly on the X-ray or CT images taken before each treatment, so the beam can be lined up with the prostate itself, which can shift a few millimeters from day to day within the pelvis.
Shorter, stronger radiation courses
Many men now have higher doses over fewer days, sometimes as few as 5 treatments. Precise aim and rectal protection make these schedules safer.
Better bowel quality of life
Men in trials who received a spacer reported fewer lasting bowel problems than men who did not.

Other options

Radiation without a spacer
Many men do well with modern radiation alone. The spacer is optional, and your radiation oncologist can tell you how much it is likely to help in your case.
Aiming without gold markers
Some centers line up the beam using the prostate's own outline on daily CT or MRI images, or use small electronic beacons instead of gold markers.
Markers placed through the rectum
Some teams place the gold markers through the rectal wall with an ultrasound probe, similar to a transrectal biopsy, which needs antibiotics.
Surgery instead of radiation
Removing the prostate is another main treatment option, with a different pattern of side effects.

Getting ready

Tick items off as you go. Your checklist is saved on this device only.

1 to 2 weeks before

Scheduling with radiation

Your radiation team schedules this visit to fit your radiation start date. The planning scan usually follows 1 to 2 weeks later.

MRI review

Your MRI is checked first. A spacer may not be advised if the cancer clearly grows out of the back of the prostate toward the rectum.

Blood thinners

Tell your team about any blood thinner. You may be asked to pause some for a few days. Never stop one on your own.

Allergies

Tell your team about allergies to numbing medicines, antibiotics, iodine contrast or latex.

The day before

Arrange a ride if you will have sedation

If you are having sedation or anesthesia, someone must drive you home.

Eating

With local numbing only, you can usually eat normally. For sedation, follow the fasting instructions you are given.

The morning of

Enema

Many teams ask you to use a small enema 1 to 2 hours before, so the rectum is empty for clear ultrasound pictures.

Medicines

Take your usual medicines unless told otherwise. Some teams give one antibiotic dose before the procedure.

The procedure, step by step

Press play or pick a step. Each drawing shows what your surgeon is doing at that moment. Your team may do some steps differently.

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1. Getting into position

You lie on your back with your legs raised in padded supports. The scrotum is gently lifted out of the way, and the skin of the perineum is cleaned. You are numbed, sedated, or put to sleep, depending on the plan.

You lie on your back with your legs raised in padded supports. The scrotum is gently lifted out of the way, and the skin of the perineum is cleaned. You are numbed, sedated, or put to sleep, depending on the plan.
A lubricated ultrasound probe is placed in the rectum to show the prostate and the space behind it. If you are awake, the skin of the perineum and the deeper tissue are numbed with lidocaine, which stings for a few seconds.
A thin needle carrying a gold marker is passed through the perineal skin into the prostate under ultrasound, and the marker is pushed out of the needle tip. This is repeated so that usually three markers sit spread apart in different parts of the prostate.
More detail
Spreading the markers out lets the radiation team see not only where the prostate is each day, but also whether it has tilted or rotated. Many teams place the markers before the gel; some do the gel first.
Watching a long view of the prostate on ultrasound, your doctor guides a needle into the thin layer between the prostate and the rectum. A small amount of salt water is injected first. If it spreads in a thin, even layer, the needle is in the right place and not in the rectal wall.
More detail
This step, called hydrodissection, opens the space and confirms the needle position before any gel goes in. It is the key safety step of the procedure.
The gel goes in as a liquid through the same needle in one steady push and turns into a soft solid within seconds. It forms a cushion, about 10 milliliters (2 teaspoons), that holds the rectum roughly 1 centimeter away from the prostate.
More detail
On ultrasound the gel looks like a dark band between the prostate and the rectum. One type of gel contains iodine so it also shows clearly on CT scans used for radiation planning.
The probe is removed, gentle pressure is held on the skin, and a small dressing goes on. About 1 to 2 weeks later, you have your planning scan, where the markers and gel are mapped before radiation begins.

After the procedure

Right afterward

A short rest
You rest for 15 to 30 minutes, or longer after sedation.
Passing urine
Some teams ask you to pass urine before leaving. Slight blood is normal.
Going home
Most people go home within an hour. If you had sedation, someone must drive you.

At home

Soreness
The perineum may be sore and bruised for 1 to 3 days. Acetaminophen and a cushion help.
Rectal pressure
Some men feel pressure or fullness in the rectum, or a feeling of needing a bowel movement, for a few days as they get used to the gel.
Blood in urine or semen
Some blood in the urine for a day or two, and in the semen for a few weeks, is common.
Bowels
Eat normally and avoid constipation and straining.
Activity
Light activity the next day is fine. Avoid heavy lifting, bicycle riding and hard exercise for 2 to 3 days.
Work and driving
Most people return to work and driving the next day, or after sedation has fully worn off.

Recovery timeline

Day 0
Procedure day
The procedure takes about 20 to 45 minutes, and you go home the same day.
Days 1 to 3
Settling in
Soreness and rectal pressure ease.
1 to 2 weeks
Planning scan
A CT scan, and often an MRI, maps the prostate, markers and gel for your radiation plan.
2 to 4 weeks
Radiation begins
Before each treatment, a quick image finds the markers so the beam can be lined up precisely.
About 3 months
Gel holds through radiation
The gel stays in place through the radiation course and then starts to soften.
About 6 months
Gel absorbed
The most common gel is largely absorbed by about 6 months. The gold markers stay in the prostate for good and are harmless.

What it feels like

Most men find this an easy step on the way to radiation. The hardest part is often the position and the probe, and the odd feeling of pressure in the rectum for a few days.

Before the procedure
Another procedure on top of a cancer diagnosis can feel like a lot, and some men are embarrassed by the position.
What helpsAsk the team to explain each step. Ask about sedation if you are anxious.
During
Pressure from the probe, a sting from the numbing, and a pinch or push as the needles go in. Some men feel a brief fullness as the gel goes in.
What helpsSlow breathing helps. Tell the team if anything feels sharp.
The first few days
Soreness when sitting and a feeling of rectal fullness or needing to have a bowel movement.
What helpsSit on a cushion, take acetaminophen, and keep your stools soft. The feeling fades within days.
Starting radiation
Many men are relieved to find that daily treatments are quick and painless once the markers are in.
What helpsFollow the bladder and bowel instructions your radiation team gives, such as drinking water before each session.

How well it works

Success means the markers are well spread through the prostate and the gel sits evenly behind it, so radiation can be aimed precisely with the rectum kept farther away.

Checked on the planning scan
Your radiation team confirms the marker positions and measures the gap the gel has created.
Daily alignment
The markers are used before each treatment to line up the beam with the prostate.
Fewer bowel side effects
The benefit is measured over the years after radiation, as fewer rectal and bowel problems.

Risks

Every operation has risks. These are the ones people ask about most, with honest odds where good numbers exist. Your surgeon’s own results matter more than averages.

Common

Soreness and bruising

The perineum may be sore and bruised for a few days.

Rectal pressure or discomfort

A feeling of fullness or pressure for a few days.

Blood in urine or semen

Usually mild and short-lived.

Less common

Trouble passing urine

Swelling can make it hard to pass urine for a short time, occasionally needing a catheter.

Infection

Infection is uncommon, especially when needles go through the perineum, and is treated with antibiotics.

Marker movement

A marker can occasionally move or be lost. The radiation team can usually still plan with the others, or a marker may be replaced.

Uneven gel placement

Gel placed more to one side gives less protection on the other side. Treatment still goes ahead, planned around it.

Rare

Gel in the rectal wall

Gel injected into the rectal wall can rarely cause pain, an ulcer, an abscess, or an abnormal channel (fistula) that needs further treatment.

Serious infection or abscess

A pocket of infection near the gel is rare and may need drainage.

Allergic reaction

A reaction to the gel, numbing medicine or antiseptic is rare.

Call your care team or go to the emergency room if

Fever of 101°F (38.3°C) or higher, or shaking chills.
Rectal pain that is severe or getting worse after the first few days, especially with fever.
Bleeding from the rectum that is more than a streak, or bloody or black stools.
You cannot pass urine, or only dribbles, with a full, painful lower belly.
Thick blood or clots in the urine.
Bleeding from the perineum that does not stop with 10 minutes of firm pressure.

Questions to ask your surgeon

Do you recommend both the spacer and the gold markers for me, and why?
Which type of gel will you use, and how long does it last?
Will the markers go through the perineum or through the rectum?
Will I be awake, sedated or asleep?
Is there anything on my MRI that makes the spacer less suitable?
When is my planning scan, and when does radiation start?
Do I need antibiotics?
Is the spacer covered by my insurance?

Words you may hear

Rectal spacer: A gel injected between the prostate and the rectum to move the rectum away from radiation.
Hydrogel: A water-based gel that is injected as a liquid and becomes a soft solid.
Fiducial marker: A tiny gold seed placed in the prostate to help aim radiation precisely.
Image-guided radiation therapy (IGRT): Taking a quick image before each treatment to line up the beam with the prostate.
Hydrodissection: Injecting a little salt water to open a tissue layer and confirm needle position.
Simulation (planning scan): The CT and often MRI scan used to design your radiation plan.
Stereotactic body radiation therapy (SBRT): Radiation given in a few high-dose sessions, often 5.
Perineum: The area between the scrotum and the anus.

Common questions

Is the spacer permanent?

No. The gel is absorbed over several months, after radiation is finished. The gold markers stay for good and cause no harm.

Will I feel the gel?

Some men feel rectal pressure for a few days. After that, most men do not notice it.

Can I have an MRI with gold markers?

Yes. The markers are safe in MRI scanners. Tell the MRI staff you have them.

Do I need a spacer for radiation?

It is optional. Many men do well without one. Your radiation oncologist will explain how much it is likely to help you.

Will the markers set off airport detectors?

No. They are tiny and not radioactive.

Sources this page draws on

International Journal of Radiation Oncology, Biology, Physics, Hydrogel spacer prospective multicenter randomized controlled pivotal trial: dosimetric and clinical effects of perirectal spacer application in men undergoing prostate image guided intensity modulated radiation therapy (2015)
International Journal of Radiation Oncology, Biology, Physics, Continued benefit to rectal separation for prostate radiation therapy: final results of a phase III trial (2017)
American Society for Radiation Oncology, American Society of Clinical Oncology and American Urological Association, Hypofractionated Radiation Therapy for Localized Prostate Cancer: An ASTRO, ASCO, and AUA Evidence-Based Guideline (2018)
American Cancer Society, Radiation Therapy for Prostate Cancer

Written November 2026. This page explains what usually happens. It is not medical advice and does not replace a conversation with your own surgeon, whose plan for you comes first.