KEY POINTS
- This single-institution retrospective cohort included 872 of 940 consecutive patients treated with five-fraction prostate SBRT from 2016–2024 who completed at least one urinary or bowel EPIC assessment within 36 months. Median age was 72 years, 40% had high-risk disease, 32% received long-term androgen deprivation, and 61% received a rectal spacer.
- Prescribed doses ranged from 36.25 to 47.5 Gy in five nonconsecutive fractions. The lower-dose group included 672 patients receiving ≤40 Gy, while 200 received >40 Gy: 67 received 42.5 Gy, 127 received 45 Gy, and six received 47.5 Gy.
- Urinary irritative/obstructive symptoms worsened acutely in both groups. Adjusted EPIC urinary scores fell at one month from 88.7 to 70.7 with ≤40 Gy and from 90.1 to 68.5 with >40 Gy, followed by recovery; however, the higher-dose group showed a more pronounced secondary decline during 18–24 months, with a significant time-by-dose interaction (P<.001).
- Clinically meaningful late urinary deterioration occurred in 68% with ≤40 Gy versus 80% with >40 Gy (P=.007). Using the stricter threshold of twice the minimal clinically important difference, late worsening remained more frequent after dose escalation at 48% versus 71% (P<.001).
- After adjustment for age, long-term androgen deprivation, rectal spacer use, treatment era and baseline urinary score, doses >40 Gy remained associated with greater odds of late urinary deterioration: OR 1.83 (95% CI 1.12–3.00; P=.016). Secondary measures including IPSS and urinary-incontinence EPIC scores showed similar less favorable late trajectories with higher dose.
- Bowel outcomes did not show the same dose relationship. Late clinically meaningful bowel worsening occurred in 54% versus 61% (P=.188), and higher dose was not independently associated with late bowel deterioration (OR 1.34, 95% CI 0.87–2.07; P=.184). Rectal spacer use was independently associated with lower odds of late bowel worsening (OR 0.57; P=.036).
- Interpretation is complicated by major treatment-era differences: 93% of the >40-Gy group versus 39% of the ≤40-Gy group were treated from 2021 onward, and rectal spacers were used in 85% versus 54%, respectively. The study did not evaluate whether dose escalation improved tumor control, clinician-reported toxicity was incomplete, and follow-up beyond 36 months was insufficient for comparative analysis.
CLINICAL TAKEAWAY
Escalating five-fraction prostate SBRT beyond 40 Gy may come at a meaningful cost in late urinary quality of life, even when contemporary rectal protection keeps bowel outcomes relatively stable. Because this was a retrospective, era-confounded comparison without oncologic efficacy data, it supports caution and patient counseling rather than defining an optimal SBRT dose.