What is the contouring volume of brachytherapy (internal radiation therapy) volumes in endometrial cancer?

From the Guidelines

For contouring brachytherapy volumes in endometrial cancer, I recommend following the GEC-ESTRO guidelines which define three key target volumes: High-Risk Clinical Target Volume (HR-CTV), Intermediate-Risk Clinical Target Volume (IR-CTV), and Gross Tumor Volume (GTV) as supported by the most recent guidelines 1. The HR-CTV should include the entire cervix, the presumed extracervical tumor extension, and any residual disease in the uterus or parametria.

• The IR-CTV typically extends 5-15 mm beyond the HR-CTV, depending on tumor size and location.
• For imaging, MRI is preferred for volume delineation, ideally with T2-weighted sequences.
• When contouring, use both clinical examination findings and imaging to accurately define disease extent.
• The applicator should be properly positioned in the uterine cavity, with appropriate tandem length and ovoid/ring size selected based on patient anatomy.
• Organs at risk (OARs) to contour include the bladder, rectum, sigmoid, and small bowel, with dose constraints of D2cc <90 Gy EQD2 for bladder and <75 Gy EQD2 for rectum/sigmoid. This approach allows for precise dose delivery to tumor volumes while minimizing radiation to surrounding healthy tissues, improving local control rates while reducing toxicity, as seen in recent studies 1.

The use of vaginal brachytherapy alone is a reasonable choice for patients with uterine-confined endometrial cancer, as it is associated with significantly less toxicity than pelvic RT, and has shown excellent and equivalent vaginal and pelvic control rates with both adjuvant radiation approaches and no difference in OS 1.

• Patient age, tumor grade, and LVSI are highly predictive for locoregional relapse, distant relapse, OS, and DFS.
• Treatment given (EBRT vs vaginal brachytherapy) is predictive for locoregional relapse and DFS.
• The benefit of adjuvant EBRT in the highest risk spectrum of uterine-confined disease remains controversial, but most NCCN panel members feel that patients with deeply invasive grade 3 tumors should receive adjuvant treatment 1.

In terms of specific dosing regimens, high-dose–rate brachytherapy, when used as a boost after EBRT, 2 fractions of 5 to 6 Gy prescribed to the vaginal mucosa are commonly used, while for high-dose rate vaginal brachytherapy alone, commonly used regimens include 3 fractions of 7 Gy prescribed at a depth of 0.5 cm from the vaginal surface, or 5 fractions of 6 Gy fractions prescribed to the vaginal surface 1.

• Patients who undergo radiation are prone to vaginal stenosis, which can impair sexual function, and can use vaginal dilators to prevent or treat this condition.
• Dilator use can begin 2 to 4 weeks after RT is completed and can be performed indefinitely.

From the Research

Contouring Volumes for Brachytherapy in Endometrial Cancer

• The contouring volumes for brachytherapy in endometrial cancer are crucial for effective treatment 2.
• According to the NRG Oncology/RTOG Consensus Guidelines, accurate target definition is critical for the appropriate application of radiation therapy 2.
• The guidelines provide an updated consensus of clinical target volume (CTV) definitions, including the removal of all references to bony landmarks and the inclusion of the para-aortic and inferior obturator nodal regions 2.

Brachytherapy Techniques and Target Volumes

• Brachytherapy is a specific form of radiotherapy consisting of the precise placement of radioactive sources directly into or next to the tumor 3.
• The American Society for Radiation Oncology recommends RT (either vaginal brachytherapy or external beam RT) be given based on the patient's clinical-pathologic risk factors to reduce the risk of vaginal and/or pelvic recurrence 4.
• When external beam RT is delivered, intensity modulated RT with daily image-guided RT is recommended to reduce acute and late toxicity 4.

Evidence-Based Recommendations

• The task force recommends RT (either vaginal brachytherapy or external beam RT) be given based on the patient's clinical-pathologic risk factors to reduce the risk of vaginal and/or pelvic recurrence 4.
• Chemotherapy is recommended for patients with International Federation of Gynecology and Obstetrics (FIGO) stage I to II with high-risk histologies and those with FIGO stage III to IVA with any histology 4.
• Sentinel lymph node mapping is recommended over pelvic lymphadenectomy for surgical nodal staging 4.

Clinical Target Volume (CTV) Definitions

• The NRG Oncology/RTOG Consensus Guidelines provide an updated consensus of CTV definitions, including the removal of all references to bony landmarks and the inclusion of the para-aortic and inferior obturator nodal regions 2.
• The guidelines include separate contours of the following areas: vaginal cuff, obturator, internal iliac, external iliac, presacral, common iliac, and para-aortic regions 2.
• There was substantial agreement for the common iliac region, moderate agreement in the external iliac, para-aortic, internal iliac, and vaginal cuff regions, and fair agreement in the presacral and obturator regions 2.