What are the contouring guidelines for endometrial cancer?

Contouring Guidelines for Endometrial Cancer

For endometrial cancer radiotherapy treatment planning, target volume definitions should include the Gross Tumor Volume (GTV), High-Risk Clinical Target Volume (CTV-THR), and Intermediate-Risk Clinical Target Volume (CTV-TIR), with MRI-based planning being the preferred imaging modality for accurate delineation. 1, 2

Imaging Modalities for Target Definition

• MRI is the preferred imaging modality for target delineation in endometrial cancer, particularly T2-weighted sequences which provide superior soft tissue contrast for defining tumor extent 2
• CT imaging can be used when MRI is unavailable, though with less accurate soft tissue definition 3
• For patients with suspected cervical involvement, contrast-enhanced dynamic MRI is the best tool to assess cervical invasion 4

Target Volume Definitions

Primary Disease (Definitive Treatment)

• Gross Tumor Volume (GTV): Includes all visible tumor on imaging, particularly within the uterine cavity 3, 2
• Clinical Target Volume (CTV): Should encompass the entire uterus as the primary target 2
• High-Risk CTV: Should include the GTV plus a margin to account for microscopic disease spread 1
• Intermediate-Risk CTV: Includes areas at risk for subclinical disease spread beyond the high-risk CTV 1

For Brachytherapy Planning

• Modified Heyman packing technique with multiple Norman-Simon applicators (typically 3-18) can be used for optimal dose distribution 3
• Three-dimensional treatment planning should be performed with contouring of CTV, GTV, and organs at risk 3
• Dose-volume adaptation should be achieved through dwell location and time variation (intensity modulation) 3

Radiation Techniques and Dose Recommendations

• For medically inoperable endometrial cancer with clinical Stage I disease:

  • Brachytherapy alone can be used if there is no evidence of deep myometrial invasion on MRI and no lymph node involvement 2
  • In the absence of MRI, a combined approach using external beam radiotherapy and brachytherapy should be considered 2

• For adjuvant treatment:

  • Intensity-modulated radiotherapy (IMRT) with daily image-guided radiotherapy (IGRT) is recommended to reduce acute and late toxicity 5
  • Vaginal brachytherapy or external beam radiotherapy should be given based on clinical-pathologic risk factors 5

Recurrent Disease Contouring Guidelines

For vaginal recurrences of endometrial cancer, the following target volumes should be defined 1:

• Residual Gross Primary Tumor Volume (GTV-Tres): Visible tumor on imaging
• High-Risk Clinical Target Volume (CTV-THR): GTV plus margin for microscopic spread
• Intermediate-Risk Clinical Target Volume (CTV-TIR): Areas at risk for subclinical disease

Risk Stratification for Treatment Planning

Treatment planning should consider the following risk categories 4:

• Low risk: Stage Ia/Ib, grade 1 or 2, endometrioid histology
• Intermediate risk: Stage Ic, grade 1 or 2, endometrioid histology; Stage Ia/Ib, grade 3, endometrioid histology
• High risk: Stage Ic, grade 3, endometrioid histology; Stage Ia/Ib/Ic with serous, clear cell, small cell or undifferentiated histology 4

Special Considerations

• For patients with Lynch syndrome (hereditary non-polyposis colorectal cancer), who have a 30-60% lifetime risk of endometrial cancer, special attention should be paid to surveillance and treatment planning 6
• Molecular tumor profiling should be increasingly considered when making recommendations for adjuvant therapy 5
• Sentinel lymph node mapping results should inform treatment planning - patients with isolated tumor cells should be treated as node negative, while those with micrometastases should be treated as node positive 5

Common Pitfalls to Avoid

• Inadequate imaging for accurate target delineation - always use MRI when available 2
• Failing to account for the entire uterus in the CTV for primary disease 3
• Not considering molecular characterization of the tumor when available 5
• Underestimating the extent of disease in cases with cervical involvement 4