Creating a temporary safety zone between the prostate and rectum

Radiation therapy is an effective treatment for many men with prostate cancer. Modern radiation techniques are remarkably accurate, but there is one anatomical challenge: the prostate sits immediately in front of the rectum.

This means that while radiation is directed at the prostate, part of the rectum may also receive radiation.

One approach to reducing this exposure is to temporarily create a small space between the prostate and rectum before radiation treatment begins.

Barrigel® is a biodegradable hyaluronic acid rectal spacer designed specifically for this purpose.

Why does the rectum need protection?

The prostate and rectum normally sit almost against each other, separated by only a thin layer of tissue.

During prostate radiation therapy, some radiation therefore inevitably reaches the anterior wall of the rectum.

This can contribute to bowel symptoms such as:

• increased bowel frequency
• urgency
• loose stools or diarrhoea
• rectal discomfort
• mucus discharge
• rectal bleeding
• radiation proctitis

Most bowel symptoms following modern radiation therapy are mild and temporary, but occasionally they can persist or become troublesome.

The basic idea behind a rectal spacer is delightfully simple:

Prostate → spacer → rectum

Instead of asking radiation technology to perform an anatomical magic trick, we physically move the rectum a little farther away.

Even approximately 1 cm of additional separation can substantially reduce the radiation dose received by the anterior rectal wall.

What is Barrigel?

Barrigel is a sterile, biodegradable gel made from stabilised, non-animal-derived hyaluronic acid.

Hyaluronic acid occurs naturally in many tissues within the human body and is widely used in medical applications.

Barrigel is injected into the tissue plane between the prostate and anterior rectal wall before prostate radiation therapy.

The gel creates a temporary cushion that pushes the rectum away from the prostate.

Importantly, Barrigel does not treat the prostate cancer itself.

Its purpose is to protect surrounding normal tissue while radiation treats the cancer.

How is Barrigel inserted?

Barrigel is usually inserted before radiation planning.

The procedure is performed using ultrasound guidance.

A needle is passed through the skin of the perineum, the area between the scrotum and anus, rather than through the rectum.

The needle is carefully positioned between the back of the prostate and the front wall of the rectum.

Barrigel is then slowly injected while the position of the gel is continuously monitored with ultrasound.

Typically several millilitres of gel are used to create the required separation.

The procedure may be performed using:

• local anaesthetic
• sedation
• or another form of anaesthesia depending upon the patient and treating centre.

Fiducial markers used for radiation targeting may sometimes be inserted during the same procedure.

Antibiotic prophylaxis and strict sterile technique are important.

Who may benefit from Barrigel?

Barrigel may be considered for men undergoing radiation therapy for localised prostate cancer where reducing radiation exposure to the rectum is desirable.

This may include men undergoing:

Conventional external-beam radiation therapy

A spacer may reduce the amount of radiation reaching the rectum during a multi-week course of treatment.

Hypofractionated radiation therapy

Modern prostate radiation is increasingly delivered using larger doses over fewer treatment sessions.

A randomised clinical trial involving 201 men demonstrated that a hyaluronic-acid spacer significantly reduced rectal radiation exposure during hypofractionated prostate radiotherapy.

Acute grade 2 or greater gastrointestinal side effects occurred in approximately 2.9% of spacer-treated patients compared with 13.8% without a spacer.

Stereotactic body radiation therapy – SBRT

SBRT delivers relatively high radiation doses over only a few treatments. Precise protection of surrounding structures therefore becomes particularly important.

Selected salvage radiation situations

Spacer placement may occasionally be considered in more complex circumstances, although previous prostate or pelvic treatment can alter the normal tissue planes and make insertion more difficult.

These cases require individual assessment by the radiation oncologist and urologist.

When should Barrigel not be used?

Barrigel is contraindicated in patients with clinical T4 prostate cancer.

It should also be approached cautiously in men with conditions that may make insertion difficult or increase the risk of complications.

These include:

• active infection or inflammation near the injection site
• bleeding disorders
• anticoagulant or thrombolytic therapy
• significant antiplatelet medication
• known allergy to hyaluronic-acid products
• significant anorectal stenosis or anatomical abnormalities
• previous surgery causing extensive scarring around the prostate or rectum
• significant haemorrhoidal disease
• immunodeficiency or significant immunosuppressive therapy.

Anticoagulant and antiplatelet medications should not simply be stopped without medical advice. Their management needs to be individualised according to the reason they are being taken.

What are the potential side effects?

Most patients tolerate spacer insertion well.

Temporary symptoms may include:

• discomfort in the perineum
• minor bleeding or bruising
• a sensation of rectal fullness
• temporary discomfort when opening the bowels
• urinary frequency or discomfort
• weak urinary stream
• temporary constipation.

The feeling that there is “something there” behind the prostate can occur initially and generally settles.

What are the uncommon but important complications?

Although rectal spacer insertion is generally considered a low-risk procedure, it is still an invasive procedure.

Possible complications include:

• infection
• prostatitis
• bleeding or haematoma
• urinary retention
• significant rectal pain
• difficult or painful defaecation
• incorrect positioning of the spacer
• injection into the prostate
• injury to the urethra or bladder
• rectal-wall injury
• rectal ulceration or tissue necrosis
• vascular injection or embolisation
• very rarely, fistula formation or severe pelvic infection.

This is why spacer insertion should be performed by clinicians experienced in transperineal ultrasound-guided procedures.

Correct placement matters just as much as the choice of spacer.

What happens to Barrigel afterwards?

Barrigel is biodegradable.

It remains between the prostate and rectum during the period when radiation treatment is being delivered and is subsequently broken down and absorbed by the body.

No second operation is normally required to remove it.

Barrigel versus SpaceOAR®

Barrigel and SpaceOAR are designed to solve the same anatomical problem, but they use different materials.

	Barrigel	SpaceOAR
Material	Stabilised hyaluronic acid	Polyethylene glycol hydrogel
Main purpose	Separate prostate and rectum	Separate prostate and rectum
Placement	Transperineal injection	Transperineal injection
Imaging guidance	Ultrasound	Ultrasound
Biodegradable	Yes	Yes
Remains permanently	No	No
Material characteristics	Hyaluronic-acid gel that can be progressively shaped during injection	PEG hydrogel formed after injection
Radiopaque version	No equivalent to SpaceOAR Vue	SpaceOAR Vue contains iodine for CT visibility
Evidence	Randomised evidence demonstrating improved rectal dosimetry and reduced acute GI toxicity	Extensive clinical experience and randomised/prospective evidence supporting rectal dose reduction

Both therefore create a temporary physical separation between the prostate and rectum.

Is Barrigel better than SpaceOAR?

At present it would be too simplistic to say that one spacer is universally “better”.

Both can substantially reduce radiation exposure to the rectum when correctly placed.

There are, however, some practical differences.

Barrigel can be shaped during insertion

Barrigel is injected as hyaluronic-acid gel. The operator can progressively deposit and shape the material while watching the developing space with ultrasound.

This can be useful when trying to achieve an appropriate distribution behind the prostate.

SpaceOAR has a long clinical track record

SpaceOAR has been extensively studied and is widely used internationally.

SpaceOAR Vue also contains iodine, making the spacer readily visible on CT. This may be helpful when MRI is unsuitable or when CT-based radiation planning is required.

Placement may matter more than the label on the syringe

An important point is that the quality, volume and position of the spacer can significantly influence the radiation dose received by the rectum.

A 2025 real-world comparative study found differences in dosimetry between Barrigel and SpaceOAR that were strongly influenced by the amount of spacer inserted. At comparable volumes, Barrigel performed favourably for some dosimetric measurements.

Interestingly, rectal-wall infiltration occurred in 7 of 287 SpaceOAR procedures (2.44%) and none of the Barrigel procedures in that particular study.

This does not prove that Barrigel is universally safer, but it highlights the importance of spacer material, injection technique and careful positioning.

What if Barrigel is not perfectly positioned?

One potentially useful characteristic of hyaluronic acid is that it can potentially be treated with hyaluronidase, an enzyme that breaks down hyaluronic acid.

This provides a theoretical and practical advantage if significant malposition is recognised.

The Queensland Clinical Excellence guidance specifically notes Barrigel’s potential to be hydrolysed in situations of spacer misplacement.

This does not make incorrect placement harmless, however. Prevention through meticulous ultrasound-guided insertion remains far preferable to correction afterwards.

Do all men having prostate radiation need a spacer?

No.

Modern radiation techniques such as IMRT, VMAT and image-guided radiotherapy already provide highly sophisticated targeting.

Whether a spacer provides meaningful additional benefit depends upon:

• prostate anatomy and size
• distance between prostate and rectum
• radiation technique
• radiation dose and fractionation
• previous prostate or pelvic treatment
• bowel disease
• anticoagulation
• individual risk of radiation toxicity
• and the experience of the treating radiation team.

Some patients may gain considerable benefit while others may gain relatively little.

The decision should therefore be made jointly between the patient, radiation oncologist and urologist.

What does the evidence tell us?

The European Association of Urology recognises biodegradable rectal spacers as a method of increasing the distance between the prostate and rectum and reducing rectal radiation exposure.

Evidence across rectal spacer studies suggests reductions in both acute and late grade 2 or greater rectal toxicity.

For Barrigel specifically, a multicentre randomised trial demonstrated impressive dosimetric results during hypofractionated radiotherapy.

98.5% of patients receiving the hyaluronic-acid spacer achieved at least a 25% reduction in the volume of rectum receiving 54 Gy.

The average reduction was approximately 85%.

The same study demonstrated substantially fewer acute grade 2 or greater gastrointestinal side effects in patients receiving the spacer.

These findings support rectal spacing as a useful tool for appropriately selected men receiving prostate radiation therapy.

The bottom line

Barrigel is a temporary hyaluronic-acid rectal spacer used to create additional distance between the prostate and rectum before prostate cancer radiation therapy.

It does not improve the radiation by attacking the cancer. Instead, it gives the radiation oncologist a little more anatomical breathing room.

For appropriately selected patients it can:

increase prostate-to-rectum separation → reduce rectal radiation dose → reduce the risk of bowel toxicity.

Barrigel and SpaceOAR both achieve this objective using different biomaterials. Neither should automatically be regarded as the best option for every patient.

The choice should take into account the planned radiation technique, individual anatomy, previous treatment, medical history and the experience of the treating team.

Most importantly, a rectal spacer is an additional protective tool, not a guarantee against radiation-related bowel complications.

When should I discuss a rectal spacer?

If you are considering external-beam radiation therapy or SBRT for prostate cancer, it is reasonable to ask your radiation oncologist or urologist:

“Would I benefit from a rectal spacer, and would Barrigel or SpaceOAR be more appropriate for me?”

That conversation should occur before radiation planning begins.

This information is intended for patient education and does not replace individual assessment by your urologist or radiation oncologist.

So, if you have discussed this with your radiation oncologist and you would like the benefit of protecting your rectum against the effects of radiation, come see your local Brisbane urologist, Dr Jo, to discuss this option.