Institutional Review of Ovoid Surface Dose and Physician Variability In HDR Brachytherapy: A Step Toward Vaginal Dose De-Escalation
Abstract
Purpose
The 2018 EMBRACE II study emphasizes minimizing vaginal mucosal dose during locally advanced cervical cancer brachytherapy. While traditional organs at risk include bladder, rectum, and sigmoid, vaginal mucosa dose has gained attention due to late toxicities such as vaginal stenosis. Studying vaginal dose de-escalation pathways aims to preserve sexual function and quality of life for patients post-treatment. This study investigates the relationship between vaginal dose, HR-CTV coverage, and inter-fraction variability regarding physician contouring.
Methods
We retrospectively evaluated 44 patients treated with EBRT followed by HDR brachytherapy using tandem and ovoid applicators. Vaginal dose was measured at the surface of the left and right ovoids as a percentage of prescription dose. Metrics assessed included vaginal dose relative to HR-CTV D90% to evaluate dose de-escalation affects on target coverage, as well as ovoid size correlations with vaginal dose. To assess inter-fraction variability, patients were grouped by contouring consistency: multiple physicians across fractions (34/44) versus a single physician (7/44), and differences in vaginal dose and HR-CTV volumes were analyzed.
Results
Higher vaginal doses (>150% Rx) occurred in some fractions despite lower HR-CTV D90%, suggesting increased ovoid loading did not improve target coverage. Vaginal dose generally decreased with larger ovoids. Inter-fraction variability was higher in patients contoured by multiple physicians, with 1.9-fold greater HR-CTV volume variation, 10.7% higher vaginal dose, and 35.0% higher dose standard deviation. These findings indicate contouring variability drives unnecessary vaginal dose exposure.
Conclusion
The EMBRACE II recommendations suggest vaginal dose de-escalation is feasible and can improve quality of life and preserve sexual function for women post-treatment. Vaginal dose can be safely reduced without compromising HR-CTV coverage. Inter-fraction variability, particularly from multiple physicians, contributes to excess vaginal dose, emphasizing the need for standardized contouring and physician scheduling. Implementing these findings clinically can minimize unnecessary vaginal dose and improve clinical outcomes.