The impact of brachytherapy boost and radiotherapy treatment duration on survival in patients with vaginal cancer treated with definitive chemoradiation.

PURPOSE: Vaginal cancer is a rare tumor that is optimally treated with a combination of chemotherapy (CHT) and radiation therapy. Because of the rarity of this cancer, the benefit of a brachytherapy boost (BT) and the relevance of radiotherapy time to treatment completion (TTC) are unclear.

METHODS

Patients diagnosed between 2004 and 2015 with non-metastatic vaginal cancer treated with definitive CHT and external beam radiotherapy with or without BT but with no surgery were identified in the National Cancer Database. Overall survival (OS) was assessed with Kaplan-Meier curves, and differences between groups were compared with the log-rank test. A Cox model was constructed to evaluate survival after controlling for confounders. A Cox model using a penalized spline function was constructed to evaluate how the length of radiation therapy correlated with OS among patients receiving BT.

RESULTS

A total of 1094 patients who met the inclusion criteria were identified. The utilization of BT was associated with improved 5-year OS (62.9% vs. 49.3%, p = 0.0126) on propensity score-weighted analyses. TTC of 63 days or less was associated with improved 5-year OS (67.8% vs. 54.5%, p = 0.0031) in patients who underwent BT. Other factors associated with improved OS in patients who received CHT, external beam radiotherapy, and BT were younger age, absent comorbidity score, and negative lymph nodes.

CONCLUSIONS

A brachytherapy boost and shorter TTC were associated with a survival benefit in a cohort of patients with non-metastatic vaginal cancer treated with definitive chemoradiotherapy.