Is adaptive treatment planning for single-channel vaginal brachytherapy necessary?

Introduction
In vaginal cuff brachytherapy, only limited information is available about the need for individualized treatment planning or imaging. Treatment planning is still performed mostly with no contouring target volume or organs at risk and with standard plan approach. Dose prescription, fractionation, and treatment planning practices vary from site to site. Without imaging, dose must be prescribed in terms of fixed distances from a known reference, such as the applicator surface. Because of different anatomies of patients, this might lead to under-dosing of target and unnecessarily high-doses delivered to adjacent organs. Also, reliable recording of dose delivered is difficult. These various uncertainties related to standard planning and lack of imaging indicate a clear need for finding an optimal method of dose planning for vaginal cuff brachytherapy.

Material and methods
A study was conducted, in which 100 vaginal cuff brachytherapy patients’ computed tomography (CT) images with applicator in situ were retrospectively analyzed to investigate target-area coverage and critical-organ doses. In addition, 28 patients’ plans were re-planned with different planning approaches, to evaluate an optimal dose-planning strategy. From treatment plans, target coverage and organs-at-risk doses were assessed.

Results and conclusions
The analysis showed that, in order to cover distal part of the vaginal cuff, dose prescription should be a 10 mm from the tip of the applicator. Individualized image-based planning is recommended at least for first fraction. This would yield lower doses to the bladder. Rectum and sigmoid doses are not significantly affected by planning approach.