Using continuous ultrasound tracking across 341 treatment sessions, the Utah team found that patients with any rectal spacer experienced fewer clinically meaningful prostate displacement events compared to patients with no spacer at all, with the hydrogel spacer reducing those events by about 28% and the biodegradable balloon by roughly 53%. In practical terms, this means the prostate was staying closer to where the radiation beam was aimed for the duration of treatment, something patients would recognize as "the radiation is more likely to hit the target every time." The degree of stabilization appeared to scale with spacer volume and physical design, which is an important nuance: the finding here is that spacer use in general is associated with a motion benefit, with the specific device appearing to influence how much of that benefit is realized.
For clinics, the operational implications could be significant and timely. As prostate Stereotactic Body Radiotherapy (SBRT) protocols push toward ultra-short regimens of just two or five fractions rather than the traditional 40+, each individual session carries more dose-per-fraction weight, meaning a prostate that drifts even briefly is a larger problem than it would be in a conventional course. This has driven major investment in expensive real-time motion monitoring systems, most prominently MRI-linacs, which can cost $5 to $10 million and require specialized staffing. Although the authors believe that real-time intrafraction tracking remains best practice for prostate SBRT, this study raises a legitimate question about how that investment is prioritized and scaled: if a rectal spacer, placed once in a single outpatient procedure, meaningfully stabilizes prostate motion, does every program need the most resource-intensive solution available from the outset? But they do suggest a spacer-first framework worth considering: use a spacer to dampen motion and reduce rectal dose, then calibrate monitoring intensity to fractionation schedule and institutional resources. For centers already planning to use a spacer, the implant may simultaneously address two problems, rectal protection and motion management, that have historically required separate solutions.
Looking further ahead, this work connects to one of the more meaningful quality-of-life questions in prostate radiation: what happens to the structures surrounding the prostate when treatment is delivered with greater precision? The conversation about margin reduction is broader than just the posterior interface with the rectum, where the spacer itself already provides a physical buffer against dose spillover. The more clinically consequential opportunity may lie laterally and anteriorly, where the neurovascular bundles responsible for erection run in close proximity to the prostate. Tighter margins in these regions, enabled by a more stationary prostate, could translate into meaningfully better preservation of sexual function, one of the outcomes men fear most when facing prostate cancer treatment. This is not purely hypothetical: the pivotal randomized trial of the biodegradable balloon spacer (Song et al.), presented at a major oncology meeting, reported that patients receiving the balloon experienced not only better rectal function but also better preservation of urinary and sexual quality of life compared to those without a spacer, a broader protection profile than has historically been associated with spacer use. If motion stabilization is part of the mechanism behind those outcomes, reducing the chance that radiation strays toward sensitive structures during any given treatment session, then the clinical case for routine spacer use in prostate SBRT strengthens considerably, independent of which specific device a center chooses. For patients, the message may ultimately be straightforward: a spacer placed before radiation may not only protect the bowel but also help preserve the quality of life that matters most after treatment is done.
Written by: Benjamin V. Tward,1 Martin Szegedi,2 Jonathan D. Tward2
- Department of Statistics, University of Michigan, Ann Arbor, Michigan.
- Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.