What are the target volume delineations, doses, and critical Organ At Risk (OAR) constraints for External Beam Radiation Therapy (EBRT) and Vaginal Brachytherapy (VBT) in post-operative endometrial carcinoma?

Target Volume Delineations, Doses, and OAR Constraints for Post-Op Endometrial Carcinoma Radiotherapy

For post-operative endometrial carcinoma patients, pelvic EBRT should target the pelvis with doses of 45-50 Gy in standard fractionation, while vaginal brachytherapy should be delivered to the upper vagina with doses of 7 Gy × 3 fractions at 0.5 cm depth or 6 Gy × 5 fractions to the vaginal surface when used alone. 1, 2

Target Volume Delineations

External Beam Radiation Therapy (EBRT)

• Pelvic EBRT targets:

  • Gross disease (if present)
  • Lower common iliac lymph nodes
  • External iliac lymph nodes
  • Internal iliac lymph nodes
  • Parametrium
  • Upper vagina/para-vaginal tissue
  • Presacral lymph nodes (especially in patients with cervical involvement) 1, 2

• Extended-field EBRT (when indicated):

  • Includes all pelvic targets above
  • Entire common iliac chain
  • Para-aortic lymph node region
  • Upper border should extend at least to the level of renal vessels 1, 2

Vaginal Brachytherapy (VBT)

• Target volume: Limited to the upper vagina after hysterectomy 1, 2
• Prescription point:
  • Either to vaginal surface or at a depth of 0.5 cm from vaginal surface 1, 2

Radiation Doses

EBRT Doses

• Microscopic disease: 45-50 Gy delivered with multiple conformal fields based on CT-treatment planning 1, 2

VBT Doses

• When used as boost after EBRT:

  • High-dose rate (HDR): 4-6 Gy × 2-3 fractions prescribed to vaginal mucosa 2
  • Alternatively: 5-6 Gy × 2 fractions to vaginal mucosa 1

• When used alone (without EBRT):

  • HDR: 7 Gy × 3 fractions prescribed at 0.5 cm depth from vaginal surface 1, 2
  • Alternative regimen: 6 Gy × 5 fractions prescribed to vaginal surface 1, 2

• For preoperative therapy in stage IIB disease:

  • Total dose of 75-80 Gy low-dose rate equivalent to the tumor volume 1, 2

Critical Organ At Risk (OAR) Constraints

While specific OAR constraints aren't explicitly detailed in the guidelines, clinical practice indicates the following constraints should be observed:

• Rectosigmoid: Cumulative D2cc (EQD2) should be limited to <75 Gy 3
• Bladder: Cumulative D2cc (EQD2) should be limited to <90 Gy 3

Treatment Selection Algorithm

1. Stage IA, Grade 1-2:

   • Preferred: Observation
   • For patients ≥60 years and/or with LVSI: VBT strongly recommended 4

2. Stage IA, Grade 3:

   • Preferred: VBT (especially if surgically staged)
   • If no myometrial invasion: Observation may be considered
   • If age ≥70 years or LVSI present: Consider EBRT (category 2B) 4

3. Stage IB, Grade 1-2:

   • Preferred: VBT
   • If no adverse risk factors: Observation may be considered
   • For grade 2 tumors with age ≥60 years and/or LVSI: Consider EBRT 4

4. Stage IB, Grade 3 with adverse risk factors:

   • EBRT and/or VBT
   • Consider adding systemic therapy (category 2B) 4

5. Stage II:

   • After radical hysterectomy with negative margins: EBRT (preferred) and/or VBT 4

Clinical Considerations and Caveats

• Timing of adjuvant RT: Should be initiated after vaginal cuff healing but no later than 12 weeks post-surgery 4

• VBT vs. EBRT selection: The PORTEC-2 trial demonstrated that VBT is as effective as EBRT in preventing vaginal recurrence in intermediate-risk patients, with significantly fewer gastrointestinal toxicities 5

• Combined modality considerations: Adding VBT to EBRT has not shown significant clinical benefit over EBRT alone in most cases, as vaginal control rates with EBRT alone are excellent 6

• Special case - Stage II disease: For patients with cervical stromal involvement, a brachytherapy boost after EBRT may be appropriate, though high-quality evidence specifically supporting this practice is lacking 6

• Vaginal stenosis prevention: Patients receiving radiation should be counseled about using vaginal dilators beginning 2-4 weeks after RT completion to prevent or treat vaginal stenosis 1

• Re-irradiation considerations: For vaginal recurrence in previously irradiated patients, salvage re-irradiation with 3D conformal brachytherapy is feasible when cumulative doses to surrounding organs are limited 3