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preliminary prostate online-adaptive salvage

Daily adaptation improved target coverage and rectal sparing in postoperative prostate radiotherapy

Daily adaptation increased prostate-bed coverage from 92.1% to 98.5% and reduced high-dose rectal exposure during hypofractionated salvage radiotherapy.

RadOncToday · ·1 min read

KEY POINTS

  • DART-PHASER is a prospective observational study of cone-beam computed tomography-guided daily adaptive salvage radiotherapy after prostatectomy. This interim analysis included 42 patients and 840 fractions; 38% had biochemical relapse only, 62% had macroscopic recurrence and 40.5% received pelvic nodal treatment.
  • Patients received 55 Gy in 20 fractions for biochemical-only relapse or 59 Gy in 20 fractions for macroscopic recurrence. When indicated, pelvic lymphatics received 45 Gy.
  • For each fraction, Ethos generated a scheduled plan recalculated on the daily anatomy and an adapted plan reoptimized after physician-reviewed contouring. The adapted plan was selected in 837 of 840 fractions.
  • Median prostate-bed planning target volume V95% improved from 92.1% with scheduled planning to 98.5% with adaptation (p < 0.0001). Pelvic nodal V95% improved from 96.55% to 98.8%, while nodal V107% decreased from 1.2% to 0.6%.
  • Median rectum V52.8 Gy decreased from 16.9% to 12.8%, a reduction of 4.1 percentage points (p < 0.0001). Rectal mean dose per fraction decreased from 1.54 to 1.42 Gy, moving below the prespecified 1.5 Gy threshold.
  • Bladder mean dose did not differ significantly, and the 0.4-percentage-point increase in bladder V40.8 Gy with adaptation was statistically significant only in the fraction-level analysis and not clinically meaningful. Bowel maximum-dose differences were also negligible.
  • End-of-treatment grade 2 gastrointestinal toxicity was 4.8%, while grade 2 cystitis occurred in 2.4% at treatment completion and 9.5% at three months. No grade 3 or higher toxicity occurred; pelvic irradiation was associated with diarrhoea (p = 0.002).

CLINICAL TAKEAWAY

Daily online adaptation substantially restored intended prostate-bed coverage and reduced rectal dose during moderately hypofractionated postoperative salvage radiotherapy. The workflow appears feasible with limited early toxicity, but it remains unknown whether these dosimetric gains reduce late toxicity or improve biochemical control; the planned study requires 184 patients.

SOURCE

Clinical and Translational Radiation Oncology