Impact of air cavity formation on dosimetry in vaginal cuff brachytherapy: a phantom study

A single-channel vaginal cylinder is the most commonly used technique for postoperative vaginal cuff brachytherapy. However, air pockets can form during cylinder insertion, displacing the vaginal wall from the applicator and potentially causing inadequate dose distribution around the vaginal cuff. It compromises the treatment outcomes and could result the treatment failure. This study investigates the impact of air cavity formation on dosimetry using a PMMA phantom simulating vaginal cuff brachytherapy. Air cavities of different sizes were introduced around the applicator and at the apex of the central catheter to assess dosimetric variations. CT-based treatment planning was done for both air cavity and non-air cavity setups, using the same parameters as for clinical cases. The dose distribution was measured using radiochromic films placed between the phantom slabs. The presence of air pockets reduces the dose coverage around the vagina and particularly at the apex of the vaginal cuff. The detailed description of the methodology and results obtained from phantom dosimetry is given in the paper. (author)