What are the indications for Radiation Therapy (RT) after Robotic-Assisted Radical Prostatectomy (RARP)?

Indications for Radiation Therapy After Robotic-Assisted Radical Prostatectomy

Radiation therapy after RARP is indicated for patients with adverse pathologic findings including seminal vesicle invasion, positive surgical margins, and extraprostatic extension due to demonstrated reductions in biochemical recurrence, local recurrence, and clinical progression. 1

Adjuvant Radiation Therapy Indications

Adjuvant radiotherapy refers to treatment delivered after surgery when PSA is undetectable but adverse pathologic features are present:

• Seminal vesicle invasion 1
• Positive surgical margins, especially if diffuse (>10 mm margin involvement or ≥3 sites of positivity) 1
• Extraprostatic extension 1
• Pathologic T3 disease 1
• Gleason score 8-10 1
• Short PSA doubling time (<9 months) 1

Adjuvant RT is typically administered within 1 year after RARP, once surgical side effects have improved or stabilized 1.

Salvage Radiation Therapy Indications

Salvage radiotherapy is indicated when there is evidence of disease recurrence after surgery:

• Biochemical recurrence (PSA ≥0.2 ng/mL with a second confirmatory level ≥0.2 ng/mL) 1
• Detectable PSA that increases on two subsequent measurements 1
• Local recurrence with no evidence of distant metastatic disease 1

Salvage RT is most effective when:

• Pretreatment PSA is <1 ng/mL 1
• PSA doubling time is slow 1

Evidence Supporting Post-RARP Radiation Therapy

Three major randomized controlled trials provide high-level evidence for adjuvant RT:

• SWOG 8794 trial (425 men with extraprostatic cancer): Adjuvant RT reduced PSA relapse and disease recurrence with improved 10-year biochemical failure-free survival for high-risk patients (36% vs 12% for observation; p=.001) 1

• EORTC trial (1005 patients with extraprostatic extension or positive margins): 5-year biochemical progression-free survival significantly improved with RT compared to observation for patients with positive surgical margins (78% vs 49%) 1

• German study by Wiegel et al. (268 patients with pT3 disease): Postoperative radiation improved 5-year biochemical progression-free survival compared to observation alone (72% vs 54%; HR, 0.53) 1

Technical Aspects of Radiation Therapy

• Recommended prescribed doses: 64-70 Gy in standard fractionation 1
• Minimum dose should be 64-65 Gy 1
• Target volumes include the prostate bed 1
• Pelvic lymph nodes may be irradiated, but pelvic radiation is not necessary in most cases 1

Special Considerations

Positive Lymph Nodes

When positive lymph nodes are found during or after RARP, management options include:

• ADT (category 1 option) 1
• Observation (category 2A for very low-risk or low-risk patients; category 2B for intermediate, high, or very high-risk patients) 1
• Addition of pelvic RT to ADT (category 2B) 1

Potential Pitfalls and Caveats

• Not all patients with adverse pathology will experience recurrence, so the risk of unnecessary radiation exposure must be weighed against potential benefits 1
• Patients with certain comorbidities or prior pelvic surgeries may have increased risk of radiation-related complications 1, 2
• Radiation therapy may impact urinary continence and erectile function recovery after RARP 1, 3
• Delaying radiation therapy until biochemical recurrence (salvage approach) may miss the window of opportunity for cure in high-risk patients 1, 4

Decision Algorithm

1. Assess pathology report after RARP for adverse features (positive margins, seminal vesicle invasion, extraprostatic extension, Gleason 8-10) 1
2. If adverse features present, consider adjuvant RT within 1 year of surgery 1
3. If no adverse features or if observation chosen initially, monitor PSA every 3-6 months 1
4. If PSA becomes detectable (≥0.2 ng/mL) and confirmed, consider salvage RT, especially if PSA <1 ng/mL 1
5. Consider addition of ADT to RT for high-risk features, though optimal protocols remain under investigation 1, 5