Background and purpose: To assess the accuracy of gross tumour volume (GTV) delineation for head and neck squamous cell carcinoma (HNSCC) using a diagnostic position MRI (MRI-D) deformably registered to the planning CT (pCT), by comparison with a dedicated planning position MRI (MRI-RT).
Material and methods: Fourteen patients with HNSCC underwent a T1-weighted MRI-D and MRI-RT. A reference GTV was defined as that delineated on MRI-RT rigidly registered to pCT. GTVs were delineated on: MRI-D and then registered to pCT by deformable image registration over the whole image (DIR-whole); MRI-D and then registered to pCT with rigid registration over a region of interest defined as GTV+3cm (Rigid-ROI); and on the pCT alone. These were compared using positional metrics to the reference.
Results: GTVs delineated on MRI-D followed by DIR-whole were significantly more accurate than those delineated on CT alone. The mean Dice Similarity Coefficient was 0.6 and 0.72 for pCT and DIR-whole respectively. Use of MRI-D with Rigid-ROI provided no advantage over CT-only delineation.
Conclusions: Contouring on MRI-RT rigidly registered to pCT should be considered as the gold standard for HNSCC. In radiotherapy centres lacking a dedicated MRI-RT, the use of an MRI-D with DIR-whole offers a significant advantage for the accuracy of GTV delineation over contouring on pCT alone.
Keywords: Diagnostic MRI; Head and neck; Image registration.
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