Exclusive MRI-based tandem and colpostats reconstruction in gynaecological brachytherapy treatment planning

According to the GYN GEC-ESTRO Recommendations, MRI is needed with the modality of T2 weighted. CT-MR compatible tandem plus colpostats (T/C) (Nucletron) is widely used in cervical brachytherapy. The major challenge of MRI is the lack of dummy catheters. Therefore, an additional imaging modality is usually required. One disadvantage of sliced-based reconstruction is that resolution in longitudinal directions can be affected by the slice thickness. The aim of this study is to present a modified T/C applicator in which the catheter visibility is significantly improved.

A modification to the existing T/C applicator has been made available, increasing the catheter entrance diameter. It allows a greater dummy catheter diameter, and consequently it can be filled with more material per unit length. Visibility was studied with different materials.

The catheter filled with saline water plus iodine compound was clearly seen in both axial and longitudinal acquisitions. To avoid uncertainties introduced by the slice thickness, a simple procedure is presented using longitudinal acquisitions.

The modified applicator plus catheter allows a powerful signal in T2 weighted MRI, using a very simple and accessible material. Also, a method is proposed to solve the problem of the uncertainty derived from slice thickness using few longitudinal acquisitions.