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April 1, 2026

Impact of Intraprostatic Simultaneous Integrated Boost on Long‐Term Outcomes in Unfavorable Intermediate‐Risk Prostate Cancer Treated With Dose‐Escalated Radiotherapy and Short‐Term Androgen Deprivation Therapy

Key Points

To determine the impact of simultaneous integrated boost on outcomes in patients with unfavorable intermediate-risk prostate cancer treated with dose-escalated radiotherapy and short-term androgen deprivation therapy.
Retrospective analysis of 194 patients treated from 2010 to 2023.
All received image-guided radiotherapy to 78 Gy with short-term androgen deprivation therapy.
A subgroup received an MRI-guided intraprostatic boost up to 86 Gy at clinician discretion.
Biochemical recurrence-free survival, distant metastasis-free survival, and prostate cancer-specific mortality were the primary endpoints.
Statistical analyses included multivariable Cox and competing-risk regression models.
After 105 months of follow-up, 8-year biochemical recurrence-free survival was 93.7% and distant metastasis-free survival was 95.7%.
No significant difference in biochemical recurrence-free survival (93.5% vs 93.6%) or distant metastasis-free survival (94.6% vs 96.7%) with intraprostatic boost.
Positive biopsy cores ≥ 50% was the only independent predictor of lower biochemical recurrence-free survival on multivariable analysis.
Low treatment-related toxicity was observed without significant differences in late gastrointestinal or genitourinary toxicity between groups.

Abstract

ABSTRACT Background Unfavorable intermediate‐risk prostate cancer (UIR‐PCa) represents a biologically heterogeneous subgroup with a higher risk of recurrence compared with favorable intermediate‐risk disease. Contemporary management frequently includes dose‐escalated radiotherapy (RT) combined with short‐term androgen deprivation therapy (ADT). Whether additional intraprostatic dose escalation using a simultaneous integrated boost (SIB) provides incremental oncologic benefit in this setting remains uncertain. Methods We retrospectively analyzed 194 patients with UIR‐PCa treated at three institutions between 2010 and 2023. All patients received image‐guided intensity‐modulated or volumetric modulated arc RT to 78 Gy with short‐term ADT. An MRI‐guided intraprostatic SIB (up to 86 Gy) was delivered in 77 patients (39.7%) at clinician discretion. Primary endpoints were biochemical recurrence‐free survival (bRFS), distant metastasis‐free survival (DMFS), and prostate cancer–specific mortality (PCSM). Multivariable Cox and competing‐risk regression models were used to assess predictors of outcome. Results After a median follow‐up of 105 months, 8‐year bRFS and DMFS rates for the entire cohort were 93.7% and 95.7%, respectively. Addition of SIB was not associated with improved bRFS (93.5% vs 93.6%, p = 0.36), DMFS (94.6% vs 96.7%, p = 0.15), or PCSM. Percent positive biopsy cores ≥ 50% was the only independent predictor of inferior bRFS on multivariable analysis. Treatment‐related toxicity was low in both groups, with no significant differences in late grade ≥ 2 gastrointestinal or genitourinary toxicity. Conclusions In patients with UIR‐PCa uniformly treated with dose‐escalated, image‐guided RT and short‐term ADT, long‐term oncologic outcomes were excellent. The addition of an intraprostatic SIB was safe but did not confer measurable improvement in biochemical or distant disease control. These findings support a selective rather than routine use of focal intraprostatic dose escalation in contemporary UIR‐PCa management.

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