Rectal Spacers May Reduce Toxicity of Proton Therapy in Prostate Cancer

At the 2026 American Society for Radiation Oncology (ASTRO) Annual Meeting, Marcio A. Fagundes, MD, discussed how the physical properties of proton therapy and the use of rectal spacers may limit gastrointestinal and genitourinary toxicity in patients with prostate cancer in an interview with CancerNetwork®. Fagundes is vice chair of Radiation Oncology, director of International Outreach, and a radiation oncologist at Baptist Health Herbert Wertheim Cancer Institute (WCI) in Miami, Florida.

Fagundes presented disease control outcomes from 404 patients with prostate cancer treated with intensity-modulated proton therapy at his institution between 2018 and December 2023. He noted that the current report focused on disease control. A forthcoming analysis will compare adverse effects between patients treated with and without a rectal spacer.

Transcript:

CancerNetwork: Given the sharp distal dose falloff of proton beams, what adverse effects do you expect to avoid, and how are rectal spacers used to reduce doses to the rectum?

Fagundes: Proton therapy has a unique property: the beam goes in and stops at a depth in the body that we can control. With proton therapy, we are decreasing the exposure of the intestines and bladder, for example, to doses of radiation that you do not really need to deliver. You can reduce the dose with proton therapy, and we do expect that [adverse] effects will be reduced. In this report, we focused on disease control, but in the next report I am working on, we are comparing [adverse] effects in patients treated with vs without a rectal spacer.

What is a rectal spacer? It is a device that we inject between the rectum and the prostate to push the rectum away from the prostate. That decreases the amount of radiation the rectum receives and makes the radiation treatment safer. Most patients are candidates for a rectal spacer. Some patients may have tumors infiltrating the capsule of the prostate, right where the rectum is, and these patients are not candidates for rectal spacer placement.

For most patients who are candidates for rectal spacers, though, the radiation dose is lower because we move the rectum away, and the treatment is safer. Patients virtually never have [adverse] effects like irritation of the rectum, called proctitis, which could cause rectal bleeding similar to a hemorrhoid. That goes away, but we can prevent it by using a rectal spacer.

Reference

Fagundes MA, Hassan H, Rodrigues M-A, et al. Intensity modulated proton therapy (IMPT) for localized prostate cancer: disease control outcomes in intermediate to very-high risk patients. Presented at: 2026 ASTRO Annual Meeting; September 26-30, 2026; Boston, MA. Abstract PQA 06.