What are the post-operative radiation therapy (RT) contouring guidelines for carcinoma of the endometrium (Ca endometrium) after a bilateral salpingo-oophorectomy (BSO)?

Post-Operative Radiation Therapy Contouring Guidelines for Endometrial Carcinoma After BSO

For post-operative radiation therapy in endometrial carcinoma, target volume contouring should be risk-adapted: vaginal brachytherapy alone targets the vaginal cuff and upper vagina for intermediate-risk disease, while external beam pelvic radiation encompasses the entire pelvis including common iliac, external iliac, internal iliac, obturator, and presacral nodal regions for high-risk or stage II disease, with consideration for combined modality (EBRT + vaginal brachytherapy boost) in stage IIB or high-risk features. 1, 2

Risk Stratification Determines RT Approach and Volumes

The contouring strategy fundamentally depends on surgical-pathologic risk factors:

Low-Risk Disease (No RT Indicated)

• Stage IA, Grade 1-2 endometrioid histology with <50% myometrial invasion and no adverse features requires observation only 1, 2
• No radiation therapy contouring is needed for this group 1, 3

Intermediate-Risk Disease (Vaginal Brachytherapy)

• Stage IA-IB with Grade 2-3, or deep myometrial invasion warrants vaginal brachytherapy alone 1, 2
• Vaginal brachytherapy target volume includes the vaginal cuff plus 2-3 cm of proximal vagina 1, 2
• The PORTEC-2 trial demonstrated equivalent pelvic control with vaginal brachytherapy compared to external beam RT but with significantly less toxicity 1
• Typical prescription is 21 Gy in 3 fractions or 15 Gy in 2 fractions to 5mm depth 2

High-Risk/Stage II Disease (External Beam ± Brachytherapy)

For Stage IIB (cervical stromal invasion) or high-risk Stage I disease, external beam pelvic radiation is indicated 1, 3

External Beam RT Contouring Volumes:

Clinical Target Volume (CTV) should encompass:

• Entire pelvic nodal regions: common iliac, external iliac, internal iliac, obturator, and presacral nodes 1
• Vaginal cuff and upper 3-4 cm of vagina 4, 5
• Parametrial tissues 1
• Upper border typically at L4-L5 or L5-S1 interspace to cover common iliac nodes 1
• Inferior border extends 3-4 cm below vaginal cuff or to inferior aspect of obturator foramen 4

Planning Target Volume (PTV):

• Add 7-10 mm margin to CTV for setup uncertainty and organ motion 2

Typical dose prescription: 45-50.4 Gy in 1.8-2.0 Gy fractions 1, 6

Stage IIB or High-Risk Features (Combined Modality)

Combined external beam RT plus vaginal brachytherapy boost is recommended for:

• Stage IIB with cervical stromal invasion 1, 3, 4
• Positive or close surgical margins 7, 5
• Lymphovascular space invasion 1, 5
• Lower uterine segment involvement 1

Sequential approach:

• External beam RT to pelvis (45-50.4 Gy) followed by vaginal brachytherapy boost (10-15 Gy to vaginal surface) 3, 4
• Vaginal brachytherapy target includes vaginal cuff plus upper 2-3 cm 4

Stage III-IV Disease (Extended Field Considerations)

For Stage IIIC with para-aortic node involvement:

• Extended field RT may include para-aortic nodal region from renal vessels to common iliac bifurcation 1
• However, systemic chemotherapy is now preferred over extended field RT for Stage III-IV disease 1, 2
• Combined chemoradiotherapy (PORTEC-3 approach) is recommended for high-risk Stage III disease 2

Critical Contouring Considerations and Pitfalls

Organs at Risk (OARs) to Contour:

• Bladder, rectum, sigmoid colon, small bowel, femoral heads, and bone marrow 2
• Dose constraints: rectum V40Gy <60%, bladder V45Gy <50%, small bowel V45Gy <200cc 2

Common Pitfalls to Avoid:

Inadequate superior coverage: Failing to extend pelvic field to L4-L5 misses common iliac nodes in patients with cervical involvement 1, 5

Excessive vaginal length in brachytherapy: Treating entire vaginal length increases toxicity without improving outcomes; limit to upper 3-4 cm maximum 1, 2

Omitting vaginal boost in Stage IIB: External beam alone provides suboptimal vaginal cuff control; combined modality is standard 3, 4

Using whole abdominal RT: This approach is obsolete due to excessive toxicity and inferior outcomes compared to chemotherapy 2

Overtreatment of low-risk patients: Stage IA Grade 1-2 with <50% invasion does not benefit from any RT 1, 2

Evidence Quality and Nuances

The PORTEC-1 and PORTEC-2 trials established that vaginal brachytherapy alone provides equivalent pelvic control to external beam RT for intermediate-risk disease with significantly less toxicity 1, 8. However, these trials specifically excluded Stage IC Grade 3 disease, which remains controversial 1.

For Stage II disease, the evidence base is weaker, with most data from retrospective series showing excellent pelvic control (96% in one series) with surgery plus adjuvant RT 4, 5. Recent National Cancer Database analysis shows increasing use of combined EBRT + VBT for Stage II disease, particularly with high-risk features like positive margins or lymphovascular space invasion 5.

The PORTEC-3 trial demonstrated improved 5-year overall survival with chemoradiotherapy versus RT alone for high-risk endometrial cancer, fundamentally changing practice for Stage III disease 2.