A verification study of proposed pelvic lymph node localisation guidelines using nanoparticle-enhanced magnetic resonance imaging

Background and purpose: Normal sized pelvic lymph nodes are not easily identifiable on conventional imaging, but can be visualised with contrast-enhanced magnetic resonance imaging (MRI) using intravenous ultra-small particles of iron-oxide (USPIO). We have previously reported pelvic node clinical target volume (CTV) delineation guidelines for use with conventional imaging, derived from nodal mapping studies using USPIO. This study aims to verify these guidelines using an independent observer in a further patient cohort. Materials and methods: Ten patients with gynaecological cancer underwent MRI with and without intravenous USPIO. The guidelines were used to outline a pelvic node CTV on pre-contrast T2-weighted images. On post-contrast T2*-weighted images the pelvic nodes were identified and outlined. The pre- and post-contrast images were co-registered and CTV examined for node coverage. Results: By applying the guidelines, full coverage of 737 of 741 node outlines was achieved (> 99%). Four nodes were not completely encompassed, two anterior external iliac nodes and two lateral external iliac nodes. Conclusions: MRI with USPIO contrast enabled the production of guidelines for localising a pelvic node CTV with conventional imaging. Application of these guidelines to a further patient cohort resulted in coverage of 99.5% node outlines demonstrating the reliability of this technique. (c) 2008 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and OncoLogy 89 (2008) 192-196.