Preferably a preplanning MRI is to be done prior to brachytherapy to help plan applicator selection and to identify ideal interstitial (IS) catheter positions and depth to optimise tumour coverage. However, due to resource limitations, this is not achievable. Therefore, initially the first fraction is performed with no IS.
Utilizing the post insertion MRI from fraction 1, brachytherapists simulate the position and depth of potential catheter insertions for the subsequent fractions in respect to clinical need and proximity of simulated needles to organs at risk
The aim of this retrospective study was to assess the dosimetric benefit of using catheter insertions from fraction one as the standard protocol for all patients.
Between 2018 and 2020, 20 patients treated with brachytherapy for cervical cancer using the Venezia applicator were retrospectively planned using simulated interstitial catheters for fraction one with a length of 2cm where they were clinically needed based on the tumour. Channels were chosen in relation to the target volume and the proximity of the catheter insertion from organs at risk (OARs).
The use of interstitial catheters for all fractions using the insertion of 2cm of different channels for first fraction increased the total HR-CTV coverage for all patients whilst ensuring the OARs remained within departmental tolerance. Catheter placement and depth were then assessed prior to subsequent fractions to assess the need for additional catheters and increased insertion depth.
The introduction of interstitial catheters with the Venezia applicator for all fractions improves HR-CTV coverage whilst the addition of interstitial catheters allows increased opportunity to reduce organs at risk dose, keeping doses within departmental tolerances. This procedure has now become the standard departmental practice.