Background
RTOG Gastrointestinal Committee consensus contouring atlas. Nine expert radiation oncologists defined elective CTVs (CTVA internal iliac/presacral/perirectal; CTVB external iliac; CTVC inguinal) for IMRT planning in anal and rectal cancer; consensus by binomial maximum-likelihood estimation at 95% threshold.
Interventions and follow up
Treatment: RTOG consensus atlas standardizing CTV/elective nodal contouring for anal and rectal cancer radiotherapy
Primary endpoint: Consensus contour definitions for IMRT planning
mFollow up: Not applicable
Primary endpoint: Consensus contour definitions for IMRT planning
mFollow up: Not applicable
Results
CTVA (all cases): Internal iliac, presacral, perirectal nodes
CTVB (anal T3–T4 or N+): External iliac nodes
CTVC (anal, below dentate line, T2–T4): Bilateral inguinal nodes
Key feature vs GYN/GU atlases: Mesorectal coverage included in CTVA for both anal and rectal cases
Recommended PTV expansion: 0.5–1.0 cm uniform margin
CTVB (anal T3–T4 or N+): External iliac nodes
CTVC (anal, below dentate line, T2–T4): Bilateral inguinal nodes
Key feature vs GYN/GU atlases: Mesorectal coverage included in CTVA for both anal and rectal cases
Recommended PTV expansion: 0.5–1.0 cm uniform margin
Adverse events
Toxicity: Not applicable
Type: Consensus guideline / contouring atlas, not a treatment study
Type: Consensus guideline / contouring atlas, not a treatment study
Conclusions
The RTOG consensus atlas provides standardized CTV definitions for IMRT planning of anal and rectal cancer, enabling consistent target delineation across institutions and prospective trials (e.g., RTOG 0529).
Key Limitations
Expert-opinion consensus, not validated against clinical outcomes; based on CT (not MRI) delineation; predates routine functional imaging; nodal coverage recommendations may evolve with newer evidence.
Clinical Context
Reference standard for elective nodal CTV delineation in anal/rectal IMRT; underpinned RTOG 0529 and remains widely used for quality assurance and trial contouring.