Nodal Volumes for Postoperative Endometrial Cancer Radiation Contouring
For postoperative radiation therapy in endometrial cancer, the nodal clinical target volume (CTV) should include the external iliac, internal iliac, obturator, and presacral lymph node regions for pelvic radiation, with extension to include the common iliac and para-aortic nodes up to the level of the renal vessels when extended-field radiation is indicated. 1, 2
Standard Pelvic Nodal Coverage
The baseline pelvic radiation target should encompass the following nodal regions 1, 2, 3:
- Lower common iliac nodes - the distal portion of the common iliac chain 1, 2
- External iliac nodes - the entire external iliac nodal basin 1, 2, 4
- Internal iliac nodes - the complete internal iliac nodal region 1, 2, 4
- Obturator nodes - the obturator nodal basin 4, 3
- Parametrial tissue - soft tissue adjacent to the uterine bed 1, 2
- Upper vagina and paravaginal tissue - the upper 3 cm of vagina with surrounding soft tissue 1, 2, 3
- Presacral nodes - particularly important in patients with cervical stromal involvement 1, 2, 3
Extended-Field Coverage Indications
Extended-field radiation therapy should include the entire common iliac chain and para-aortic lymph node region up to at least the level of the renal vessels in the following clinical scenarios 1, 2, 5:
- Documented common iliac lymph node involvement 1, 4
- Para-aortic lymph node metastases 1, 4
- High-risk tumor features including 1:
- Deeply invasive lesions (>50% myometrial invasion)
- High-grade histology (Grade 3)
- Serous adenocarcinoma
- Clear cell adenocarcinoma
- Carcinosarcoma
The upper border of extended-field radiation depends on the clinical situation but must extend at minimum to the renal vessels, and potentially higher if directed by the distribution of involved nodes 1, 2, 4.
Modern Contouring Technique
CT-based treatment planning with vessel-based contouring is the contemporary standard approach 6, 3. The 2021 NRG Oncology/RTOG consensus guidelines provide the most current specifications 6:
- Contour the iliac vessels (common, external, and internal) and apply appropriate margins to define nodal CTVs 6, 7
- A 7-10 mm expansion around the iliac vessels (excluding bone and muscle) provides optimal nodal coverage while minimizing normal tissue inclusion 6, 7
- The obturator region requires special attention as it shows the least inter-observer agreement and may need manual adjustment beyond simple vessel expansion 6
- All bony landmark references have been removed from modern guidelines in favor of vessel-based and anatomic soft tissue definitions 6
Critical Technical Considerations
Avoid using symmetrical geometric expansions alone for inguinofemoral nodes - these require specific anatomic boundaries based on muscle groups 8. For endometrial cancer, inguinal nodes are not routinely included unless there is involvement at or below the dentate line 9.
The presacral nodal region shows fair inter-observer agreement (kappa 0.36) and requires careful attention to ensure adequate coverage, particularly in patients with cervical involvement 6.
Planning target volume (PTV) expansion of 0.5-1.0 cm from the CTV is standard to account for setup uncertainty and organ motion 6, 10.
Dose Specifications
External beam doses for microscopic nodal disease should be 45-50 Gy in conventional fractionation (1.8-2.0 Gy per fraction) 1, 2. Multiple conformal fields based on CT treatment planning must be used 1, 2.
For gross unresected adenopathy, highly conformal boosts of an additional 10-15 Gy may be considered to limited volumes 4.