Prostate Brachytherapy Boost Versus EBRT in a Patient With Prior TURP
A 70-year-old man with Gleason 4+4=8, PSA 12.4 ng/mL, cT2c prostate cancer, prostate volume 78 cc, IPSS 18, on warfarin for atrial fibrillation, and prior transurethral resection of the prostate 6 years ago. He is offered either external beam radiotherapy 78 Gy in 39 fractions with 6 months of androgen deprivation, or external beam 45 Gy in 25 fractions plus low-dose-rate brachytherapy boost. Planning MRI shows a large median lobe and a urethra within 4 mm of the prostate apex. The brachytherapy plan would deliver urethra D0.1cc 130 Gy and rectal V100 1.2 cc; the EBRT plan has rectal V70 12% and bladder V65 18%. He is active but has nocturia three times per night and wants to avoid a urinary catheter.
1. Is this patient a suitable candidate for a low-dose-rate brachytherapy boost? Justify your answer using the clinical and dosimetric details.
Read the worked answer
He is a poor candidate for LDR brachytherapy boost. Relative contraindications include prior TURP, large prostate volume (78 cc), high IPSS (18), and anticoagulation. Prior TURP increases the risk of urinary incontinence and urethral necrosis; a large gland makes seed placement and dose homogeneity harder; high IPSS predicts acute urinary retention; warfarin increases bleeding and seed migration risk. The proposed urethra D0.1cc of 130 Gy is high and would raise urethral stricture and necrosis risk, especially with a median lobe and apex proximity. Rectal V100 of 1.2 cc is not necessarily prohibitive, but the combination is unfavorable. EBRT 78 Gy in 39 fractions with androgen deprivation is safer, although rectal V70 12% and bladder V65 18% need review. If brachytherapy is still considered, it should be after urology review, withholding anticoagulation per protocol, and with a preplan that keeps urethra D0.1cc below institutional tolerance and rectal V100 <1 cc; but the overall risk-benefit favors EBRT.
2. If EBRT alone is chosen, what dose constraints and planning priorities would you use for the rectum, bladder, and urethra?
Read the worked answer
For EBRT, prioritize target coverage while respecting typical constraints: rectal V70 <15–20%, rectal Dmax <75 Gy, bladder V65 <20–25%, bladder Dmax <80 Gy, femoral heads Dmax <50 Gy, and urethra Dmax <80 Gy if tracked. Use a rectal spacer if available, daily image guidance with fiducials or cone-beam CT, and intensity-modulated radiotherapy. Because of prior TURP, avoid hot spots at the urethra and bladder neck; because of anticoagulation, monitor hematuria. Do not sacrifice PTV coverage to meet a marginal rectal constraint without discussing the risk of biochemical failure. If the rectal V70 remains 12% and bladder V65 18%, the plan is likely acceptable; check the dose to the membranous urethra and penile bulb if potency matters.