Image-guided moderately hypofractionated proton beam therapy for localized prostate cancer: 5-year outcomes of a phase II trial.
Takashi Iizumi, Hitoshi Ishikawa, Yuta Sekino et al.
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In 30 seconds
This phase II clinical trial evaluated image-guided, moderately hypofractionated proton beam therapy (63 Gy RBE in 21 fractions) in 125 men with histologically confirmed localized prostate cancer (cT1c-3aN0M0). At a median follow-up of 71.0 months (IQR: 60-84), the 5-year cumulative incidence of late grade 2 or higher gastrointestinal adverse events was 3.3%, meeting the primary endpoint. The 5-year biochemical recurrence-free rate was 97.6% (95% CI: 94.9-100.0); no clinical recurrences were observed. The authors concluded that this schedule had low late toxicity and was feasible.
Key findings
- The 5-year cumulative incidence of late grade 2 or higher gastrointestinal adverse events was 3.3%; the primary endpoint was met.
- Late grade 2 or higher genitourinary adverse events had a 5-year cumulative incidence of 8.1%.
- The 5-year biochemical recurrence-free rate was 97.6% (95% CI: 94.9-100.0); three biochemical recurrences were observed.
- No clinical recurrences occurred; 5-year clinical recurrence-free and overall survival rates were 100% and 97.5% (95% CI: 94.8-100.0), respectively.
Why it matters
These results provide longer-term phase II evidence on both toxicity and disease control with a 21-fraction proton schedule in men with localized prostate cancer. The low reported incidence of late gastrointestinal events and absence of clinical recurrence are relevant when assessing the feasibility of this regimen, while the trial design and population define the scope of the evidence.
What to keep in mind
The evidence comes from a phase II trial in 125 men; the abstract does not report a comparator group.