Five-Treatment Prostate SBRT: What the PACE-B Trial Found

Short answer: For selected people with localized prostate cancer, stereotactic body radiation therapy (SBRT) delivered in five treatments controlled cancer as well as conventional or moderately shortened radiation in the randomized PACE-B trial. The shorter schedule is convenient, but the trial also found a higher cumulative rate of moderate-or-worse urinary side effects.

What is prostate SBRT?

SBRT uses detailed imaging, planning, and highly precise radiation delivery to give a larger dose at each visit. A typical prostate SBRT course has five treatments over one to two weeks. Longer external-beam schedules may use 20 or 39 treatments.

Fewer visits do not mean less careful treatment. The prostate can move as the bladder and rectum change, so reproducible preparation, image guidance, and strict dose limits remain important.

What did PACE-B compare?

PACE-B was an international phase 3 randomized trial. It enrolled 874 people with localized prostate cancer:

• stage T1 or T2 disease;
• a Gleason score of 3+4 or lower;
• a PSA of 20 ng/mL or lower; and
• mostly intermediate-risk disease.

Participants received either five-fraction SBRT or a control schedule of 20 or 39 fractions. Hormone therapy was not permitted. That detail matters: the result should not automatically be extended to every high-risk case or to treatment plans that include androgen-deprivation therapy.

Cancer control at five years

After a median follow-up of about 6.2 years, freedom from biochemical or clinical failure at five years was:

• 95.8% with five-treatment SBRT
• 94.6% with the control schedules

The result met the trial's prespecified definition of noninferiority. In plain language, SBRT did not perform meaningfully worse than the longer schedules for the study's main cancer-control outcome.

This is strong evidence for the people represented in the trial. It is not proof that every five-treatment technique, dose, or patient selection process will produce the same result.

What side effects did the trial report?

At five years, cumulative grade 2 or higher urinary toxicity was 26.9% after SBRT and 18.3% after control radiotherapy. Grade 2 effects can include symptoms that require medication or otherwise affect daily life. Cumulative bowel toxicity was similar: 10.7% with SBRT and 10.2% with control treatment.

These numbers require context. “Cumulative incidence” counts an event if it happened at any point during the follow-up period; it does not mean every affected person had a persistent symptom at five years.

A later PACE-B analysis found that baseline urinary symptoms, use of urinary medication, and significant early urinary toxicity were associated with later urinary effects. This supports discussing urinary function before selecting SBRT.

What about intermediate- or high-risk disease?

PACE-C is studying five-treatment SBRT against 20-treatment radiotherapy in intermediate- and high-risk prostate cancer with six months of hormone therapy. Its early safety analysis found similar early bowel toxicity. Early urinary toxicity was numerically higher with SBRT, and the trial's cancer-control endpoint is not yet mature.

PACE-C should therefore be described as an important ongoing evidence update—not as completed proof of equal cancer control for high-risk disease.

Questions to discuss before choosing a schedule

Ask your radiation oncologist:

1. Which risk group and stage do I have?
2. How do my current urinary symptoms affect the choice?
3. Will hormone therapy be recommended?
4. How will the prostate be localized at each treatment?
5. What bladder and rectal preparation is required?
6. What urinary, bowel, and sexual effects are most relevant to me?

The best schedule is the one that fits the cancer and the person—not simply the option with the fewest visits.

Questions patients often ask

Does five-treatment SBRT cure prostate cancer?

PACE-B showed excellent five-year cancer control in the trial population, but no treatment can promise a cure for an individual. Risk group, imaging, health, anatomy, and follow-up all affect outcomes.

Is five-treatment SBRT safer than longer radiation?

It is more convenient, but not automatically safer. PACE-B reported similar bowel toxicity and more cumulative grade 2 or higher urinary toxicity with SBRT. A clinician should discuss the different tradeoffs.

Does everyone with localized prostate cancer qualify?

No. PACE-B primarily studied low- and intermediate-risk disease. People with substantial urinary symptoms, different risk features, or anatomy that makes dose constraints difficult may be better served by another approach.

Sources and further reading

1. Phase 3 Trial of Stereotactic Body Radiotherapy in Localized Prostate Cancer. The New England Journal of Medicine (2024).
2. Exploring Factors Associated with Late Urinary Toxicity After Prostate SBRT: Findings from PACE-B. European Urology (2025).
3. Intensity-modulated moderately hypofractionated radiotherapy versus SBRT for prostate cancer (PACE-C). The Lancet Oncology (2025).