Vaginal Brachytherapy Boost Following EBRT in Endometrial Cancer
Adding a vaginal brachytherapy boost to external beam radiation therapy (EBRT) in endometrial cancer is generally not recommended and provides no clear benefit for vaginal control, while increasing toxicity and side effects. 1
Evidence Against Routine VBT Boost After EBRT
Stage I-II Intermediate and High-Intermediate Risk Disease
The PORTEC-2 trial definitively showed that vaginal brachytherapy alone provides equivalent vaginal control compared to EBRT, with vaginal recurrence rates of approximately 2% at 5 years after either modality alone. 1 This finding was confirmed by a Swedish trial comparing EBRT alone versus combined EBRT with vaginal brachytherapy boost, which showed no additional benefit from the boost. 1
Multiple retrospective studies examining Stage I-II endometrial cancer found no difference in local recurrence or overall survival rates among patients treated with or without vaginal brachytherapy in addition to EBRT. 1 A large retrospective analysis of 270 patients receiving adjuvant pelvic radiation (173 with EBRT alone versus 97 with EBRT plus vaginal brachytherapy) found no difference in 5-year pelvic control or disease-free survival rates between groups. 2
Stage II Disease with Cervical Stromal Invasion
For Stage II disease, controversy exists regarding the role of vaginal brachytherapy boost, but evidence does not support routine use. 1 The indication for brachytherapy boost is clear only in the rare situation of positive vaginal margins. 1 In the adjuvant setting without positive margins, studies have found no difference in local recurrence or overall survival with the addition of vaginal brachytherapy to EBRT, but it was associated with increased risk of side effects. 1
When VBT Boost May Be Considered
Positive Vaginal Margins
The only clear indication for vaginal brachytherapy boost after EBRT is when there are positive vaginal surgical margins. 1
Isolated Vaginal Recurrence After Surgery
For isolated vaginal relapse in patients who did not receive primary adjuvant radiation, combined EBRT and brachytherapy is highly effective. 1 In the PORTEC-1 trial, 35 of 39 patients with vaginal recurrence after surgery alone were treated with radical intent using combinations of EBRT and brachytherapy, achieving an 89% complete remission rate with 77% remaining disease-free at median follow-up of 44 months. 1
Toxicity Considerations
The addition of vaginal brachytherapy boost to EBRT increases side effects without improving outcomes. 1 The PORTEC-2 trial demonstrated that vaginal brachytherapy alone had significantly lower rates of acute grade 1-2 gastrointestinal toxicity compared to EBRT (12.6% versus 53.8% at completion of radiotherapy). 3
Combined EBRT and brachytherapy for recurrent disease is associated with higher rates of side effects compared with adjuvant vaginal brachytherapy alone. 1
Risk-Stratified Approach Without VBT Boost
Intermediate-Risk (Stage I, Grade 1-2, ≥50% MI, LVSI Negative)
- Adjuvant vaginal brachytherapy alone is recommended to decrease vaginal recurrence (Level of Evidence I, Strength B). 1
- No adjuvant treatment is an option, especially for patients aged <60 years (Level of Evidence II, Strength C). 1
High-Intermediate Risk (Stage I, Grade 3 with <50% MI; or Grade 1-2 with LVSI Positive)
- If surgical nodal staging performed and node negative: Adjuvant brachytherapy alone is recommended (Level of Evidence III, Strength B). 1
- If no surgical nodal staging and LVSI unequivocally positive: Adjuvant EBRT alone is recommended (Level of Evidence III, Strength B). 1
- If no surgical nodal staging, grade 3 and LVSI negative: Adjuvant brachytherapy alone is recommended (Level of Evidence III, Strength B). 1
High-Risk (Stage I, Grade 3 with ≥50% MI)
- If surgical nodal staging performed and node negative: Adjuvant EBRT with limited fields should be considered, OR adjuvant brachytherapy alone may be considered as an alternative (Level of Evidence I and III, Strength B). 1
- If no surgical nodal staging: Adjuvant EBRT alone is generally recommended (Level of Evidence III, Strength B). 1
Common Pitfalls to Avoid
Do not routinely add vaginal brachytherapy boost to EBRT based on historical practice patterns. 1, 2 The evidence shows no benefit in vaginal control rates, which remain approximately 2% at 5 years with either EBRT alone or vaginal brachytherapy alone. 1
Do not confuse the role of vaginal brachytherapy as primary adjuvant therapy (where it is highly effective) with its role as a boost after EBRT (where it provides no additional benefit). 1, 3
Recognize that LVSI status and grade 3 histology are critical risk factors for regional nodal and distant recurrence. 1 EBRT decreases regional nodal recurrence risk in this subgroup, while vaginal brachytherapy does not. 1 Therefore, treatment selection should be based on these pathologic features rather than reflexively adding both modalities.