Clinical Outcomes After 1 Year of MR-Guided SBRT with Rectal Spacer in Localized Prostate Cancer

Overview

This prospective study evaluated the safety, toxicity, and patient-reported outcomes of MR-guided stereotactic body radiation therapy (MRgSBRT) combined with rectal spacers in localized prostate cancer patients over a median follow-up of one year. Results demonstrated low rates of acute and late gastrointestinal and genitourinary toxicities, with favorable quality of life outcomes, supporting the clinical benefit of rectal spacers in this setting.

Background

External beam radiation therapy is a standard treatment for localized prostate cancer, with hypofractionated and ultra-hypofractionated regimens like SBRT gaining popularity due to their convenience and efficacy. However, higher radiation doses per fraction raise concerns about rectal toxicity. Injectable rectal spacers have been developed to physically separate the prostate from the rectum, reducing radiation exposure to the rectal wall. MR-guided SBRT offers superior soft tissue visualization and adaptive planning capabilities, potentially enhancing the protective effects of rectal spacers. Prior studies have shown promising early results, but long-term toxicity and patient-reported outcomes data remain limited.

Data Highlights

Key Findings

• MRgSBRT combined with rectal spacers was feasible and well tolerated in localized prostate cancer patients.
• Rectal spacers effectively increased the prostate-rectum distance, reducing radiation dose to the rectal wall.
• Low rates of acute and late grade ≥2 gastrointestinal and genitourinary toxicities were observed up to one year post-treatment.
• Patient-reported outcomes indicated preservation of quality of life related to bowel and urinary function.
• MR imaging allowed clear visualization of rectal spacers, facilitating adaptive planning and management of asymmetrical spacer placement.
• Use of rectal spacers in MRgSBRT may enhance rectal protection beyond that seen in non-MR-guided radiation therapy.

Clinical Implications

The integration of rectal spacers in MR-guided SBRT protocols for localized prostate cancer can reduce rectal radiation exposure and associated toxicities, improving patient quality of life. Clinicians should consider spacer insertion prior to MRgSBRT to optimize treatment safety and efficacy. MR imaging facilitates precise spacer visualization and adaptive treatment planning, potentially further minimizing toxicity risks.

Conclusion

MR-guided SBRT with rectal spacer insertion is a safe and effective approach for localized prostate cancer, demonstrating low toxicity and favorable patient-reported outcomes at one year. These findings support the routine use of rectal spacers in MRgSBRT to enhance rectal protection and treatment tolerability.

References

1. Alongi et al. 2023 -- Preliminary patient-reported outcomes of hydrogel spacers in prostate MRgSBRT
2. MIRAGE Trial 2022 -- MR-guided vs CT-guided SBRT in localized prostate cancer
3. Boston Scientific SpaceOAR -- Rectal spacer technology