Improved delineation with diffusion weighted imaging for laryngeal and hypopharyngeal tumors validated with pathology

This study aims to determine the added value of a geometrically accurate diffusion-weighted (DW-) MRI sequence on the accuracy of gross tumor volume (GTV) delineations, using pathological tumor delineations as a ground truth.

Sixteen patients with laryngeal or hypopharyngeal carcinoma were included. After total laryngectomy, the specimen was cut into slices. Photographs of these slices were stacked to create a 3D digital specimen reconstruction, which was registered to the in vivo imaging. The pathological tumor (tumor_HE) was delineated on the specimen reconstruction. Six observers delineated all tumors twice: once with only anatomical MR imaging, and once (a few weeks later) when DW sequences were also provided. The majority voting delineation of session one (GTV_MRI) and session two (GTV_DW-MRI), as well as the clinical target volumes (CTVs), were compared to the tumor_HE.

The mean tumor_HE volume was 11.1 cm³, compared to a mean GTV_MRI volume of 18.5 cm³ and a mean GTV_DW-MRI volume of 15.7 cm³. The median sensitivity (tumor coverage) was comparable between sessions: 0.93 (range: 0.61-0.99) for the GTV_MRI and 0.91 (range: 0.53-1.00) for the GTV_DW-MRI. The CTV volume also decreased when DWI was available, with a mean CTV_MR of 47.1 cm³ and a mean CTV_DW-MRI of 41.4 cm³. Complete tumor coverage was achieved in 15 and 14 tumors, respectively.

GTV delineations based on anatomical MR imaging tend to overestimate the tumor volume. The availability of the geometrically accurate DW sequence reduces the GTV overestimation and thereby CTV volumes, while maintaining acceptable tumor coverage.