Postoperative Pelvic Radiotherapy in Endometrial Carcinoma: Contouring Atlas & Target Volume Guidelines

1. Rationale and Foundational Atlases

• Original atlas (2008): Small W Jr, Mell LK, Anderson P, et al. Int J Radiat Oncol Biol Phys 2008;71:428–34. [PMID: 18037584] — established CTV definitions using bony landmark references for IMRT in postoperative endometrial and cervical cancer.
• Updated atlas (2021): Small W Jr, Bosch WR, Harkenrider MM, et al. NRG Oncology/RTOG Consensus Guidelines for Delineation of CTV for Intensity Modulated Pelvic Radiation Therapy in Postoperative Treatment of Endometrial and Cervical Cancer: An Update. Int J Radiat Oncol Biol Phys 2021;109:413–24. [PMID: 32905846] — removed all bony landmark references, added para-aortic and inferior obturator nodal regions, and produced a 95% agreement smoothed final contour atlas from 16 international experts.

2. Risk Stratification Driving RT Decisions

3. Treatment Volume Definitions (GTV / CTV / PTV)

GTV (Gross Tumor Volume)

• Post-hysterectomy (standard postoperative setting): no GTV unless gross residual disease is present on imaging.
• If residual disease exists: GTV = known extent of disease on CT/MRI/PET.

CTV (Clinical Target Volume)

a. Vaginal Cuff CTV

• The vaginal cuff and adjacent paravaginal soft tissue (3–5 mm lateral margin).
• Upper 3 cm of vagina is the minimum treated length; in high-risk cases, the upper two-thirds of vagina.
• Kappa agreement in 2021 atlas: moderate (κ = 0.47).

b. Obturator Nodal CTV

• Nodes along the obturator vessels, medial to the external iliac vein and lateral to the bladder.
• Most variable region in contouring — fair agreement only (κ = 0.21).
• The updated 2021 atlas incorporated the inferior obturator nodal region (previously absent).

c. Internal Iliac Nodal CTV

• Vessels and surrounding tissue from the internal iliac bifurcation to the level of the posterior superior iliac spine.
• Includes presacral nodal chains anterolateral to S1–S2.
• Kappa: moderate (κ = 0.52).

d. External Iliac Nodal CTV

• Along the external iliac vessels, from the bifurcation of common iliac to the femoral ring.
• Extends 7 mm around the vessels.
• Kappa: moderate (κ = 0.60).

e. Presacral Nodal CTV

• Region anterior to S1–S2, encompassing the median sacral vessels and presacral fat.
• Only included when cervical involvement is present (stage II) or positive pelvic nodes.
• Least agreement in 2021 atlas (κ = 0.36).

f. Common Iliac Nodal CTV

• Vessels from aortic bifurcation (L4–L5) to common iliac bifurcation; 7 mm surrounding vessels.
• Best agreement among all regions (κ = 0.64).
• Included for: stage IIIC disease, cervical involvement, or high-risk features; often omitted for low-risk early-stage.

g. Para-Aortic Nodal CTV (new in 2021 atlas)

• When extended-field RT is indicated (positive para-aortic nodes or very high-risk IIIC2).
• Upper border: 1–2 cm above the level of the renal vessels (based on clinical situation).

PTV (Planning Target Volume)

• PTV = CTV + setup margin, typically 7–10 mm (may reduce to 5 mm posteriorly near rectum with daily IGRT).
• Organ motion is particularly relevant post-hysterectomy (bladder and bowel fill variability). The ITV (internal target volume) strategy incorporating bladder-filling states should be considered — some protocols treat the ITV as the CTV.

4. Standard Pelvic Field Boundaries

5. Dose Prescriptions

External Beam Radiotherapy (EBRT)

Vaginal Brachytherapy (HDR) — Postoperative Alone

6. Indications by Stage/Risk Group

7. Technical Delivery and IMRT Considerations

• Simulation: Supine with immobilization device, full bladder protocol (reduces small bowel dose), empty rectum.
• Imaging: CT simulation with IV contrast; MRI fusion recommended for nodal delineation.
• Technique: IMRT/VMAT is preferred over 3D-CRT for reduction of bowel, bladder, and bone marrow dose. RTOG 0418 validated IMRT technique for postoperative gynecological cancers.
• IGRT: Daily cone-beam CT is recommended to account for interfractional organ motion (bladder, sigmoid, small bowel), especially in post-hysterectomy patients.
• Bone marrow sparing: Use of whole-pelvic IMRT with bone marrow avoidance reduces hematologic toxicity (relevant with concurrent chemotherapy).

8. Organs at Risk (OARs) Constraints

Key References

1. Small W Jr et al. Consensus guidelines for delineation of CTV for IMRT in postoperative treatment of endometrial and cervical cancer. Int J Radiat Oncol Biol Phys 2008;71:428–34. [PMID: 18037584] — Original RTOG atlas.
2. Small W Jr et al. NRG Oncology/RTOG Consensus Guidelines — an update. Int J Radiat Oncol Biol Phys 2021;109:413–24. [PMID: 32905846] — Current standard atlas, removes bony landmarks, adds para-aortic and inferior obturator regions.
3. Nout RA et al. (PORTEC-2). Vaginal brachytherapy vs. pelvic ERT — establishes brachytherapy equivalence for vaginal control in high-intermediate risk. Lancet 2010.
4. de Boer SM et al. (PORTEC-3). Chemoradiotherapy for high-risk endometrial cancer. Lancet Oncol 2018;19:295–309.
5. China Anti-Cancer Association Brachytherapy Committee. Guidelines for radiation therapy for endometrial cancer (V 2025.1). Holistic Integrative Oncology 2025.
6. ESGO/ESTRO/ESP 2025 guidelines — incorporate molecular subtyping (MMRd, POLE, p53abn, NSMP) into RT decision-making.

— Berek & Novak's Gynecology (10th ed.), Chapter 37