KEY POINTS
- The report describes a 61-year-old man developing a solitary macroscopic prostate-bed recurrence nine years after radical prostatectomy. PSA had risen to 0.41 ng/mL, and PSMA PET/MRI identified a 2.1 × 1.5 × 1.4-cm lesion abutting and possibly infiltrating the rectal wall.
- Salvage VMAT was planned sequentially to 46 Gy/23 fractions to elective pelvic nodes, 66 Gy/33 fractions to the prostate bed and 78 Gy/39 fractions to the macroscopic recurrence, with 4–5-mm target margins.
- With an empty rectum, dose escalation to 78 Gy was not feasible under institutional constraints: rectal V70 was 27.2% and V75 24.6%, exceeding planned limits of <15% and <10%, respectively.
- A repeat simulation used an endorectal balloon inflated with 60 mL of water, physically displacing the lateral and posterior rectal wall away from the recurrent target.
- The balloon reduced rectal V70 from 27.2% to 13.4% and V75 from 24.6% to 8.6%, relative reductions of 51% and 65%, bringing both metrics within institutional constraints and permitting delivery of 78 Gy.
- Acute toxicity was limited to grade 1 urinary irritation/frequency and grade 1 diarrhea. At six months, PSMA PET showed complete resolution of the lesion with undetectable PSA; at 12 months, PSA remained undetectable without urinary or rectal complaints.
- This is a single-patient report with only 12 months of follow-up, which is insufficient to characterize late rectal toxicity after high-dose postoperative salvage RT. The authors also did not reduce the PTV margin despite the potential immobilization benefit of the balloon.
CLINICAL TAKEAWAY
An endorectal balloon may occasionally convert an otherwise impossible macroscopic prostate-bed boost into a dosimetrically feasible plan when recurrence directly abuts the rectum. The >50% reduction in high-dose rectal volume is striking, but one case cannot establish that this approach is reproducible or safe enough for routine dose escalation.