Prostate Brachytherapy Boost: 15-Year ASCENDE-RT Results

Short answer: ASCENDE-RT showed that adding a low-dose-rate prostate brachytherapy boost produced stronger long-term PSA control than an external-beam boost. At 15 years, however, the trial did not show a significant overall-survival advantage, and brachytherapy caused more serious urinary side effects.

What was ASCENDE-RT?

ASCENDE-RT enrolled 398 people with intermediate- or high-risk localized prostate cancer. Everyone received:

• 12 months of androgen-deprivation therapy;
• 46 Gy of external-beam radiation to the prostate and pelvic lymph nodes; and
• a randomized dose-escalation boost.

One group received an external-beam boost to a total dose of 78 Gy. The other received a low-dose-rate brachytherapy boost using permanent iodine-125 seeds placed inside the prostate.

Because both groups received pelvic radiation and hormone therapy, the trial isolates the effect of the boost method—not brachytherapy as a stand-alone treatment.

What did earlier results show?

The brachytherapy boost produced a large improvement in biochemical control. At 10 years, freedom from biochemical failure was:

• 85% with the brachytherapy boost; and
• 67% with the external-beam boost.

Biochemical failure is usually defined by a confirmed PSA rise after treatment. Preventing a PSA recurrence can reduce future scans, biopsies, hormone treatment, and anxiety, but it is not the same endpoint as living longer.

What changed at 15 years?

The 2026 analysis reported 213 deaths after a median follow-up of about 15 years. Overall survival was approximately:

• 60.9% with the brachytherapy boost; and
• 55.0% with the external-beam boost.

After adjustment, there was no statistically significant overall-survival difference.

The reported cumulative incidence of prostate cancer death was lower with brachytherapy—8.6% versus 16.4%—in the primary cause-of-death analysis. However, that comparison became nonsignificant when deaths with an unknown cause were counted as prostate cancer deaths. Cause-of-death uncertainty and the lack of active study follow-up after 10 years make this a signal, not definitive proof of a prostate cancer survival benefit.

What were the urinary tradeoffs?

The brachytherapy boost caused more urinary morbidity. At five years, the cumulative incidence of grade 3 urinary events was:

• 18.4% after brachytherapy boost; and
• 5.2% after external-beam boost.

Events included urinary obstruction, catheter use, incontinence, and procedures for strictures. Some resolved: the proportion of participants still experiencing grade 3 urinary morbidity at five years was lower than the cumulative event rate.

The original technique and treatment era also matter. Contemporary imaging, seed placement, dosimetry, and patient selection may reduce some risks, but the randomized toxicity result should not be dismissed.

Who might discuss a brachytherapy boost?

The option is most often considered for selected people with unfavorable intermediate-risk or high-risk localized disease who:

• have acceptable baseline urinary function;
• can undergo anesthesia and an implant procedure;
• have anatomy suitable for seed placement; and
• value maximum local and biochemical control despite greater procedural and urinary burden.

Significant urinary obstruction, a very large prostate, prior transurethral surgery, bleeding risk, or limited access to experienced brachytherapy teams can affect suitability.

How should the result be interpreted today?

ASCENDE-RT remains important because it is randomized and has unusually long follow-up. Yet it began before several current approaches—including MRI-guided focal boost, modern moderate hypofractionation, five-treatment SBRT, and newer systemic intensification—became common.

The best conclusion is specific: an LDR brachytherapy boost improved biochemical control compared with the external-beam boost used in this trial, at the cost of more urinary toxicity. It did not establish a statistically significant overall-survival advantage at 15 years.

Ask a radiation oncologist how brachytherapy boost compares with modern external-beam options for your risk group, urinary function, anatomy, and treatment priorities.

Questions patients often ask

What is a prostate brachytherapy boost?

It is an additional high dose delivered from radioactive sources placed inside the prostate after external-beam radiation. ASCENDE-RT used permanent low-dose-rate iodine-125 seeds.

Did a brachytherapy boost improve overall survival?

No significant overall-survival difference was found at 15 years, although the brachytherapy group had substantially better long-term biochemical control.

Is brachytherapy boost appropriate for everyone with high-risk prostate cancer?

No. Baseline urinary function, prostate size, anatomy, anesthesia fitness, prior procedures, cancer risk, and access to an experienced brachytherapy team all matter.

Sources and further reading

1. Fifteen-Year Survival Analysis From the ASCENDE-RT Randomized Trial. Journal of Clinical Oncology (2026).
2. ASCENDE-RT: An Analysis of Survival Endpoints. International Journal of Radiation Oncology, Biology, Physics (2017).
3. ASCENDE-RT: An Analysis of Treatment-Related Morbidity. International Journal of Radiation Oncology, Biology, Physics (2017).