Post-Operative Radiation Therapy Contouring Guidelines for Endometrial Carcinoma After TAH-BSO
For post-operative radiation therapy contouring in endometrial carcinoma after TAH-BSO, the target volumes must be risk-stratified: intermediate-risk disease requires vaginal cuff plus 2-3 cm of proximal vagina for brachytherapy alone, while high-risk or stage II disease mandates a clinical target volume (CTV) encompassing the entire pelvic nodal regions (common iliac, external iliac, internal iliac, obturator, presacral nodes), vaginal cuff, upper 3-4 cm of vagina, and parametrial tissues, with an upper border at L4-L5 or L5-S1 interspace. 1
Risk Stratification Framework
The contouring approach is fundamentally determined by pathologic risk factors identified at surgery:
Low-Risk Disease (No RT Needed)
- Stage IA, Grade 1-2 endometrioid histology with <50% myometrial invasion and no lymphovascular space invasion (LVSI): Observation only is recommended with no radiation therapy required 2, 1
- Follow-up alone is standard for these patients 2, 3
Intermediate-Risk Disease (Vaginal Brachytherapy)
- Stage IA-IB with Grade 2-3, or ≥50% myometrial invasion, LVSI negative: Vaginal brachytherapy alone is warranted 2, 1
- Target volume for brachytherapy: Vaginal cuff plus 2-3 cm of proximal vagina 1
- Dose prescription: 21 Gy in 3 fractions or 15 Gy in 2 fractions to 5mm depth, based on PORTEC-2 trial demonstrating equivalent pelvic control to external beam RT with significantly less toxicity 1
- For patients <60 years old, no adjuvant treatment is an option 2
High-Risk Disease (External Beam RT ± Brachytherapy)
Stage I high-risk features (Grade 3 with ≥50% myometrial invasion, regardless of LVSI status):
When Surgical Nodal Staging Performed and Node-Negative:
- Grade 1-2, LVSI negative: Vaginal brachytherapy 2
- Grade 3 or LVSI unequivocally positive: Limited field external beam RT (EBRT) 2
- Adjuvant brachytherapy is an alternative option 2
When No Surgical Nodal Staging Performed:
- Adjuvant EBRT is required 2
- Adjuvant chemotherapy (combined and/or sequential) can be considered, with greater evidence supporting combined chemotherapy plus EBRT than either modality alone 2
External Beam RT Contouring Specifications
Clinical Target Volume (CTV) Definition
For Stage IIB (cervical stromal invasion) or high-risk Stage I disease:
- Nodal regions to include: Common iliac, external iliac, internal iliac, obturator, and presacral lymph nodes 1
- Vaginal coverage: Vaginal cuff and upper 3-4 cm of vagina 1
- Parametrial tissues: Must be included in CTV 1
- Superior border: L4-L5 or L5-S1 interspace to adequately cover common iliac nodes 1
Planning Target Volume (PTV)
- Margin: Add 7-10 mm to CTV for setup uncertainty and organ motion 1
- Dose prescription: 45-50.4 Gy in 1.8-2.0 Gy fractions 1
Stage-Specific Contouring Considerations
Stage II Disease:
- Stage IIA (endocervical glandular involvement only): Postoperative vaginal brachytherapy if myometrial invasion <50% 3
- Stage IIB (cervical stromal invasion): Postoperative external pelvic radiotherapy with brachytherapy boost is standard 2, 3
Stage III Disease:
- Stage IIIA (serosa/adnexal invasion or positive peritoneal cytology): Options include postoperative pelvic radiotherapy or abdomino-pelvic radiotherapy 2, 3
- Stage IIIB (vaginal involvement): Pelvic external beam irradiation with brachytherapy 2, 3
- Stage IIIC1 (positive pelvic lymph nodes): Postoperative pelvic radiotherapy with brachytherapy boost 2, 3
- Stage IIIC2 (positive para-aortic lymph nodes): Chemotherapy plus extended field EBRT to be considered, with CTV extending to para-aortic region 2
Organs at Risk (OARs) Contouring and Dose Constraints
Mandatory OARs to contour: 1
- Bladder
- Rectum
- Sigmoid colon
- Small bowel
- Femoral heads
- Bone marrow
Dose constraints: 1
- Rectum: V40Gy <60%
- Bladder: V45Gy <50%
- Small bowel: V45Gy <200cc
Critical Pitfalls to Avoid
Common contouring errors that compromise outcomes: 1
- Inadequate superior coverage: Failing to extend CTV to L4-L5 or L5-S1 interspace results in under-coverage of common iliac nodes
- Excessive vaginal length in brachytherapy: Treating more than vaginal cuff plus 2-3 cm increases toxicity without benefit
- Omitting vaginal boost in Stage IIB: Cervical stromal invasion requires combined external beam plus brachytherapy boost
- Using whole abdominal RT: This approach showed over half of treatment failures within the radiation field with significant toxicity (grade 3/4 gastrointestinal, hematologic complications) and is not recommended 4
- Overtreatment of low-risk patients: Stage IA, Grade 1-2 with <50% invasion requires no RT
Special Histologic Considerations
Non-endometrioid histologies (serous, clear cell, undifferentiated, carcinosarcoma):
- These are considered high-risk regardless of stage 2
- Carcinosarcoma and undifferentiated tumors require aggressive combined modality therapy 2
- Systemic chemotherapy, radiosensitizing chemotherapy, or sequential radiation and chemotherapy should be considered given high rates of distant failure 4
Technical Considerations
Radiation technique impacts complication rates:
- Use of multiple fields per day (rather than single anteroposterior/posteroanterior field) significantly reduces severe complications (3% vs 40%) 5
- Proper RT technique with multiple fields can be delivered with acceptable risks even in patients who underwent lymph node sampling 5
- Age >65 years and lymph node sampling are independent risk factors for complications, requiring careful attention to dose constraints 5
Evidence Quality Notes
The PORTEC-1 and PORTEC-2 trials provide high-quality evidence that vaginal brachytherapy alone provides equivalent pelvic control to external beam RT for intermediate-risk disease with significantly less toxicity 1. The PORTEC-3 trial demonstrated improved 5-year overall survival with chemoradiotherapy versus RT alone for high-risk endometrial cancer 1. These landmark trials form the foundation for current risk-adapted contouring strategies.