Treatment for gynaecological cancers often includes brachytherapy; in particular, in high-dose-rate (HDR) interstitial
brachytherapy, hollow needles are inserted into the tumour and surrounding area through a template in order to deliver the
radiation dose. Currently, there is no standard modality for visualizing needles intra-operatively, despite the need for
precise needle placement in order to deliver the optimal dose and avoid nearby organs, including the bladder and rectum.
While three-dimensional (3D) transrectal ultrasound (TRUS) imaging has been proposed for 3D intra-operative needle
guidance, anterior needles tend to be obscured by shadowing created by the template’s vaginal cylinder. We have
developed a 360-degree 3D transvaginal ultrasound (TVUS) system that uses a conventional two-dimensional side-fire
TRUS probe rotated inside a hollow vaginal cylinder made from a sonolucent plastic (TPX). The system was validated
using grid and sphere phantoms in order to test the geometric accuracy of the distance and volumetric measurements in
the reconstructed image. To test the potential for visualizing needles, an agar phantom mimicking the geometry of the
female pelvis was used. Needles were inserted into the phantom and then imaged using the 3D TVUS system. The needle
trajectories and tip positions in the 3D TVUS scan were compared to their expected values and the needle tracks visualized
in magnetic resonance images. Based on this initial study, 360-degree 3D TVUS imaging through a sonolucent vaginal
cylinder is a feasible technique for intra-operatively visualizing needles during HDR interstitial gynaecological
brachytherapy.
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