Where are we with fractionation schedules and prescriptions in high-dose-rate 3D planning vaginal cuff brachytherapy?

PURPOSE: Currently, there are many schedules for exclusive vaginal cuff brachytherapy (VCB). In 3D treatment planning for VCB dosimetry, parameters have not been analyzed. The aim of this study was to compare the most common schedules using dose-volume histogram metrics.

MATERIAL AND

METHODS

Three different computed tomography (CT) studies for vaginal cylinders of 3.5 cm, 3 cm, and 2.5 cm were performed. Clinical target volume (CTV) was delineated for 3 cm and 4 cm of vaginal length. Twelve schedules were analyzed obtaining overall vaginal surface dose (Gy) (EQD2 α/β = 10 and α/β = 3), overall D90 CTV (α/β = 10) (Gy), and overall D2cc (α/β = 3) for organs at risk (OARs), such as vagina, rectum, sigmoid, rectum, and bladder. Prescription at 5 mm from the applicator surface and at the surface were analyzed for each case.

RESULTS

The overall vaginal surface dose and dose to CTV varied widely among the different schedules, and CTV delineation was necessary in case of surface prescription. The applicator diameter of 3.5 cm showed the best dosimetry results for vaginal surface dose. The overall D2cc OARs' doses changed in the different CT studies.

CONCLUSIONS

This dosimetry study allows for better selection of fractionation schedules, and helps to unify treatments among centers. Prospective studies are needed to establish the best schedule and CTV length in each patient using clinical data, such as late toxicity and relapses.