Prostate Brachytherapy: Comprehensive Overview
Overview of Techniques
Prostate brachytherapy delivers highly conformal radiation directly to the prostate using two distinct approaches: low-dose-rate (LDR) permanent seed implantation and high-dose-rate (HDR) temporary catheter-based treatment. 1, 2
Low-Dose-Rate (LDR) Brachytherapy
LDR brachytherapy involves permanent radioactive seed implantation into the prostate under image guidance (ultrasound or MRI). The seeds gradually lose radioactivity over time, delivering radiation at a slow rate that spares surrounding bladder and rectal tissues due to the short range of low-energy emissions 3.
Isotope options and dosing:
- Iodine-125: 145 Gy for monotherapy, 110 Gy when combined with EBRT
- Palladium-103: 125 Gy for monotherapy, 100 Gy when combined with EBRT 3
- Both isotopes are reasonable options with comparable outcomes 4
The procedure is completed in a single day under general anesthesia, with seeds implanted based on pretreatment and intraoperative computer planning 1.
High-Dose-Rate (HDR) Brachytherapy
HDR brachytherapy uses temporary catheters implanted in the prostate to deliver a high-activity radiation source (typically Iridium-192). This allows precise dose escalation, particularly when combined with EBRT 1, 5.
Common HDR dosing regimens:
- Boost with EBRT (40-50 Gy): 9.5-11.5 Gy × 2 fractions, 5.5-7.5 Gy × 3 fractions, or 4.0-6.0 Gy × 4 fractions
- Monotherapy: 13.5 Gy × 2 fractions 5
Indications by Risk Group
Low-Risk Disease (cT1c-T2a, Gleason ≤6, PSA <10 ng/mL)
LDR brachytherapy monotherapy is the primary indication, achieving >90% cancer control rates at 10 years, comparable to radical prostatectomy 3, 5. EBRT alone or radical prostatectomy are equivalent alternatives 4.
Favorable Intermediate-Risk Disease
LDR monotherapy may be offered for low-volume Gleason 3+4 disease with good urinary function (International Prostate Symptom Score <12, maximum flow rate >15 mL/min), achieving up to 85% relapse-free survival at 10 years 2.
For patients choosing EBRT, brachytherapy boost (LDR or HDR) should be offered, with or without androgen deprivation therapy (ADT) 4. Combination therapy increases complication rates but improves coverage of periprostatic space 1.
Unfavorable Intermediate-Risk and High-Risk Disease
Brachytherapy boost (LDR or HDR) combined with EBRT and ADT should be offered 4, 2. For high-risk patients receiving EBRT and ADT, adding brachytherapy boost reduced disease-specific mortality (HR 0.77,95% CI 0.66-0.90) compared to EBRT alone 5.
Trimodality treatment (EBRT + brachytherapy + ADT) for very high-risk disease (PSA >20, T3/T4, or Gleason 8-10) reduced prostate cancer-specific mortality (adjusted HR 0.32,95% CI 0.14-0.73) compared to brachytherapy alone 3.
Patient Selection Criteria
Ideal Candidates for LDR Brachytherapy
- Prostate volume appropriate for implantation (not very large or very small)
- Good baseline urinary function (IPSS <12, Qmax >15 mL/min)
- No previous TURP (or minimal channel TURP with ≥1 cm rim of tissue and ≥3 months healing time) 2
- No active inflammatory bowel disease or prior pelvic radiation 3
Poor Candidates
Patients with the following should NOT receive brachytherapy:
- High International Prostate Symptom Score or bladder outlet obstruction
- Previous extensive TURP (increased incontinence risk)
- Very large or very small prostates (though neoadjuvant ADT may shrink large prostates to acceptable size)
- Prior pelvic irradiation
- Active inflammatory disease of rectum
- Permanent indwelling Foley catheter 3, 5
Procedural Details
LDR Implantation Process
- Pretreatment imaging with ultrasound or MRI for treatment planning
- General anesthesia required
- Transrectal ultrasound guidance for seed placement
- Seeds implanted according to computer-generated plan
- Postimplant dosimetry mandatory within 30 days to document implant quality 3, 5
HDR Implantation Process
- Temporary catheter placement in prostate under image guidance
- High-activity source temporarily inserted through catheters
- Multiple fractions typically delivered
- Catheters removed after treatment completion
Side Effects and Toxicity
Acute Effects (Within 1 Year)
Genitourinary toxicity:
- Acute urinary retention risk (1.5-22%)
- Irritative voiding symptoms persisting up to 1 year post-implantation 3, 5
- Minimal incontinence risk in patients without prior TURP 3
Gastrointestinal toxicity:
- Minimal rectal toxicity due to dose sparing
Late Effects (>1 Year)
Genitourinary complications:
- Post-implantation TURP required in 8.7% of cases
- Incontinence: 0-19% (higher after prior TURP due to bladder neck contractures)
- Urethral strictures (particularly with LDR boost + EBRT)
- Progressive erectile dysfunction develops in ~40% at 3-5 years (short-term preservation better than surgery) 3, 2
Grade 3+ toxicity rates:
- LDR monotherapy: <1% late GU/GI toxicity 2
- LDR boost + EBRT: 18% late GU toxicity (vs 8% EBRT alone), including two treatment-related deaths 2
- HDR boost + EBRT: <4% grade 3-4 toxicity in most series 6
Critical caveat: Patients with prior TURP have substantially higher incontinence risk from acute retention and bladder neck contractures 3.
Follow-Up and Outcomes
PSA Monitoring
- PSA nadir value is crucial for predicting biochemical relapse-free outcome 7
- Biochemical recurrence defined by Phoenix criteria (nadir + 2 ng/mL)
- PSA may initially rise ("PSA bounce") before declining
Long-Term Outcomes
Biochemical relapse-free survival at 5 years:
- Low-risk: >85-95%
- Intermediate-risk: 69-97%
- High-risk: 63-80% 6
10-year outcomes:
- Overall survival: >85%
- Distant metastasis: <10%
- Cancer-specific mortality: <5% 6
Recent data (2026) confirms durable control: 95.3% bRFS in low-risk, 96.0% in intermediate-risk, and 94.3% in high-risk patients with permanent seed brachytherapy 8.
Key Advantages
- Single-day treatment completion with minimal time away from activities 3
- Highly conformal dose distribution sparing rectum and bladder
- Cancer control rates comparable to surgery (>90% for low-risk disease)
- Minimal incontinence risk without prior TURP
- Better short-term erectile function preservation than surgery 3
- Lower operator dependence with HDR vs LDR 6
Critical Pitfalls to Avoid
- Do not offer LDR monotherapy to high-risk patients without EBRT and ADT
- Screen carefully for prior TURP history - these patients have significantly higher complication rates
- Assess baseline urinary function - poor function predicts worse outcomes
- Ensure postimplant dosimetry is performed to verify adequate coverage
- Counsel patients that erectile dysfunction is progressive over several years, not immediate
- Do not use neoadjuvant ADT before radical prostatectomy (outside clinical trials), but it may be used to shrink prostate before brachytherapy 1