Hydrogel Spacer Receives FDA 510(k) Clearance for Prostate Cancer Radiotherapy

The FDA has cleared the SpaceOAR Flex System, a hydrogel spacer from Boston Scientific, through the 510(k) premarket notification pathway, according to the agency’s premarket notification database.¹ The FDA determined that the device is substantially equivalent to a legally marketed predicate. The 510(k) record lists the randomized HYDROSPACE trial (NCT06451614) as the supporting clinical study. That trial is evaluating a pre-formed radiopaque hydrogel for perirectal spacing in patients with low- to intermediate-risk prostate cancer who are undergoing external beam radiotherapy (EBRT).

What does the FDA clearance of the SpaceOAR Flex System cover?

Boston Scientific submitted the traditional 510(k) on June 25, 2026, and the FDA issued its substantially equivalent decision on September 11, 2026. The device is classified as a hydrogel spacer under product code OVB and regulation number 892.5725, and it was reviewed by the radiology panel. The submission was not reviewed by a third party, and the device is not a combination product. No predetermined change control plan was authorized with the clearance.

Devices in this classification are intended to temporarily position the anterior rectal wall away from the prostate during radiotherapy, with the goal of reducing radiation dose to the rectum.

What is the HYDROSPACE trial design?

HYDROSPACE is a prospective, randomized, multicenter study evaluating the safety and effectiveness of the investigational SpaceIT Hydrogel System in patients undergoing EBRT for prostate cancer. Patients in the investigational arm will receive the SpaceIT Hydrogel System. Those in the control arm will receive a commercially marketed Boston Scientific perirectal hydrogel spacer, either the SpaceOAR System or SpaceOAR Vue Hydrogel.²

Eligible patients are 18 years or older with pathologically confirmed invasive adenocarcinoma of the prostate planning to undergo EBRT. Patients must also meet the following criteria:

• Clinical stage T1 to T2c disease per the eighth edition of the American Joint Committee on Cancer (AJCC) staging system
• A Gleason score of 7 or less on a biopsy taken within 12 months of the baseline visit
• A prostate-specific antigen level of 20 ng/mL or less, measured within 6 months of baseline and before starting androgen deprivation therapy (ADT)

Concurrent ADT is permitted within protocol-defined timing windows. Key exclusion criteria include known sensitivity or allergy to polyethylene glycol and an inability to undergo a pelvic MRI.

What are the primary end points of the HYDROSPACE trial?

According to a trial-in-progress abstract presented at the 2025 American Society for Radiation Oncology (ASTRO) Annual Meeting, approximately 230 patients are expected to be randomly assigned 1:1 to the pre-formed iodinated hydrogel or to the commercially available polyethylene glycol–based hydrogel control. Enrollment is taking place at up to 35 sites in the US and Canada.³

The primary safety end point is the rate of acute grade 3 or higher adverse effects (AEs) arising within 90 days of the index procedure, including all AEs listed on the labels of commercially available hydrogel perirectal spacers. The primary effectiveness end point is a clinically relevant dose reduction among patients who receive the pre-formed radiopaque spacer. It is defined as a 25% reduction in the volume of the rectum receiving 90% of the prescribed radiation dose. The sample size was calculated based on the primary safety end point.

What is the regulatory history of SpaceOAR hydrogel spacers?

The first-generation SpaceOAR hydrogel received FDA authorization in April 2015.⁴ It is visible primarily on MRI, which typically means patients need a prostate MRI after placement for radiotherapy planning. Its successor, SpaceOAR Vue, is an iodinated hydrogel that is visible on CT, which removes the need for a post-procedure MRI for treatment planning. It received 510(k) clearance in July 2019.⁵

References

1. 510(k) premarket notification: SpaceOAR Flex System (K262151). FDA. Updated September 21, 2026. Accessed September 25, 2026. https://tinyurl.com/2vxr2tsr
2. SpaceIT Hydrogel System for perirectal spacing in subjects with low to intermediate risk prostate cancer undergoing external beam radiotherapy (EBRT). ClinicalTrials.gov. Updated September 14, 2026. Accessed September 25, 2026. https://tinyurl.com/ymmhapkf
3. Baumann BC, Desai NB, Collins SP, et al. Pre-formed radiopaque hydrogel for perirectal spacing in subjects with low to intermediate risk prostate cancer undergoing external beam radiotherapy (EBRT): a multicenter, randomized, controlled clinical study (HYDROSPACE). Int J Radiat Oncol Biol Phys. 2025;123:e534-e535. doi:10.1016/j.ijrobp.2025.06.2725
4. Device classification under section 513(f)(2)(De Novo): SpaceOAR System (DEN140030). FDA. Updated September 21, 2026. Accessed September 25, 2026. https://tinyurl.com/3z2e4jsk
5. Radiopaque hydrogel rectal spacer for prostate cancer radiation image guidance. ClinicalTrials.gov. Updated December 9, 2025. Accessed September 25, 2026. https://tinyurl.com/mpzhzymx