• "Quiz me on radiobiology"
• "Summarize the 4 Rs of radiobiology"
• "Give me high-yield points on breast cancer radiation"
• "MCQs on head and neck dosing"
• "Explain normal tissue dose constraints"

Elective Nodal Irradiation (ENI) in Carcinoma Prostate

1. Rationale

2. Patient Selection - The Roach Formula

LNI (%) = (2/3 × PSA) + (Gleason score - 6) × 10

• If LNI >15% → candidate for ENI (this has been the traditional threshold used in trials)
• Some nomograms (Partin tables, MSKCC) are also used

• High-risk disease: T3-T4, Gleason 8-10, PSA >20
• Unfavorable intermediate-risk (UIR) with adverse features
• Clinical T2c or N0 with estimated LNI >15%

3. Key Randomized Trials (EXAM CRITICAL)

RTOG 94-13 (Roach et al., 2003 / Lawton et al., 2007)

• Design: 4-arm trial - Whole pelvis vs. prostate-only RT × neoadjuvant vs. adjuvant total androgen suppression (TAS)
• Eligibility: LNI >15% by Roach formula
• Initial result (4 yr): WPRT + neoadjuvant TAS showed improved PFS (54% vs. 47%, P=0.022)
• Long-term update: Benefit in biochemical control was lost - no difference in overall survival
• Key teaching point: Interaction between ADT timing and radiation field - WPRT benefits patients who receive neoadjuvant (not adjuvant) ADT. Adjuvant ADT benefits prostate-only RT patients.

GETUG-01 (Pommier et al., 2007)

• Design: WPRT + prostate RT vs. prostate-only RT in T1b-T3 N0 non-metastatic patients
• 6 months neoadjuvant ADT allowed in high-risk group
• Result: No difference in 5-year PFS or OS; no significant difference in GI/GU toxicity or QoL
• Key teaching point: Negative trial for ENI

NRG/RTOG 0924 (Roach et al., ASTRO 2025 - most recent data)

• Design: Phase III RCT, 2473 patients with UIR or favorable high-risk (FHR) prostate cancer, LNI ≥15%
• All patients received ADT + dose-escalated RT (79.2 Gy)
• WPRT vs. prostate-only RT
• Median follow-up: 7.3 years
• Result: No improvement in overall survival with WPRT; biochemical failure rates were modestly lower in the WPRT arm (trend only)
• Conclusion: "Whether the modest trends in biochemical failure will translate into prostate cancer-specific or overall survival differences remains to be seen" (Roach, ASTRO 2025)
• Future direction: Biomarker/genomic classifier-based patient selection being explored

4. Why Past Trials May Have Been Negative - Field Design Issue

• Prior pelvic fields ended at S1/S2 or L5/S1
• Studies show the common iliac nodal station is involved in 55% of first pelvic recurrences (Spratt et al., 2017)
• A conventional field at L5/S1 would only cover 42% of first pelvic recurrences
• Extending to cover the common iliac region increases coverage to 93%
• RTOG 09-24 recommends the superior border at L4/L5 disk level

5. Target Volumes for ENI (CTV)

6. Ultra-Hypofractionation for Pelvic Nodes

• Ultrahypofractionated pelvic nodal irradiation is safe with acceptable acute toxicity
• Data is still maturing for long-term outcomes

7. RTOG 9413 - Critical ADT Interaction (High-Yield!)

"There is an interaction between timing of ADT and elective pelvic nodal radiation - patients receiving prostate-only RT benefit more from adjuvant ADT, but WPRT should not be used when ADT is given prior to RT (neoadjuvant)" - Roach et al., 2018

8. Key Summary Table

9. Current Consensus

• Prophylactic pelvic nodal RT has NOT been shown to improve disease recurrence rates or OS in randomized trials (Campbell-Walsh Wein Urology, p. 4707)
• ENI remains controversial and is offered selectively at many centers for high-risk patients with LNI >15-20%
• NCCN lists pelvic nodal RT as an option for high-risk/very high-risk disease with concurrent long-term ADT
• Ongoing trials are exploring biomarker/genomic selection (e.g., genomic classifier scores) to identify who truly benefits

Practice MCQ