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

Abstract

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 D_{2cc (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 D_2cc 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.

Keywords: endometrial cancer; schedules; vaginal-cuff brachytherapy.

Fig. 1

Dose distribution using 3.5 cm applicator diameter for 2.5 cm and 4 cm active source length and dose prescription. A) Dose distribution with 2.5 cm active length and prescription at 5 mm from applicator surface in axial, coronal, and sagittal planes. B) Dose distribution with 4 cm active length and prescription at 5 mm from applicator surface in axial, coronal, and sagittal planes. C) Dose distribution with 2.5 cm active length and prescription at applicator surface in axial, coronal, and sagittal planes. D) Dose distribution with 4 cm active length and prescription at applicator surface in axial, coronal, and sagittal planes

Fig. 2

Dose distribution using 3 cm applicator diameter for 2.5 cm and 4 cm active source length and dose prescription. A) 2.5 cm active length with prescription at 5 mm from applicator surface in axial, coronal, and sagittal planes. B) 4 cm active length with prescription at 5 mm from applicator surface in axial, coronal, and sagittal planes. C) 2.5 cm active length with prescription at applicator surface in axial, coronal, and sagittal planes D) 4 cm active length with prescription at applicator surface in axial, coronal, and sagittal planes

Fig. 3

Dose distribution using 2.5 cm applicator diameter for 2.5 cm and 4 cm active source length and dose prescription. A) Dose distribution with 2.5 cm active length and prescription at 5 mm from applicator surface in axial, coronal, and sagittal planes B) Dose distribution with 4 cm active length and prescription at 5 mm from applicator surface in axial, coronal, and sagittal planes. C) Dose distribution with 2.5 cm active length and prescription at applicator surface in axial, coronal, and sagittal planes. D) Dose distribution with 4 cm active length and prescription at applicator surface in axial, coronal, and sagittal planes