Background
Long-term update of RTOG 9413 (Roach et al, Lancet Oncology 2018). Extended ~20-year follow-up of the 4-arm factorial trial (whole pelvis RT vs prostate-only RT × neoadjuvant/concurrent ADT vs adjuvant ADT) in high-risk locally advanced prostate cancer (PSA ≤100 ng/mL, estimated pelvic LN risk ≥15% by Roach formula).
Interventions and follow up
Arm A: WPRT + neoadjuvant/concurrent ADT
Arm B: WPRT + adjuvant ADT
Arm C: PORT + neoadjuvant/concurrent ADT
Arm D: PORT + adjuvant ADT
Primary endpoint: Long-term PFS and OS
mFollow up: ~20 year
Arm B: WPRT + adjuvant ADT
Arm C: PORT + neoadjuvant/concurrent ADT
Arm D: PORT + adjuvant ADT
Primary endpoint: Long-term PFS and OS
mFollow up: ~20 year
Results
Long-term PFS: WPRT + N/C ADT numerically superior but no significant differences at 20 year (primary comparison)
Long-term OS: No significant differences between arms
Late toxicity: WPRT slightly higher late bowel toxicity vs PORT (predominantly grade 1–2)
Long-term OS: No significant differences between arms
Late toxicity: WPRT slightly higher late bowel toxicity vs PORT (predominantly grade 1–2)
Adverse events
Late bowel grade ≥3: WPRT ~5% vs PORT ~3% (long-term)
Late GU: Similar between arms
Death: No significant increase in treatment-related deaths
Late GU: Similar between arms
Death: No significant increase in treatment-related deaths
Conclusions
At 20 years, no arm showed a significant PFS or OS advantage, consistent with the 7-year Horwitz update. The early 4-year WPRT + N/C ADT benefit did not translate into a sustained survival advantage; WPRT carried a small persistent increase in late bowel toxicity. Results do not strongly support routine elective pelvic nodal irradiation in unselected high-risk patients by clinical risk stratification alone.
Key Limitations
Long-term attrition; many died of competing causes over 20 years, potentially obscuring prostate-specific differences. Pre-PSMA-PET staging — enrolled patients may have had undetected node-positive disease. Modern IMRT delivers lower bowel dose than the 4-field/conformal technique used. PSMA-PET-guided pelvic RT may recapture nodal benefit with better selection.
Clinical Context
Confirms absence of long-term advantage for elective whole pelvic RT by clinical risk estimation alone. PSMA-PET nodal staging now identifies true node-positive patients likely to benefit. SPPORT (RTOG 0534; Pollack 2022 NEJM) showed pelvic RT + ADT + salvage prostatectomy RT improved metastasis-free survival in biochemically recurrent post-prostatectomy patients, supporting targeted pelvic nodal coverage in selected patients.