Modality-specific target definition for laryngeal and hypopharyngeal cancer on FDG-PET, CT and MRI.

BACKGROUND AND PURPOSE: The goal of this study was to improve target definition by deriving modality-specific margins for clinical target volumes (CTV) for laryngeal and hypopharyngeal cancer on CT, MRI and 18-FDG-PET. MATERIAL AND METHODS: Twenty-five patients with T3/T4 laryngeal/hypopharyngeal cancer underwent CT, MRI and 18-FDG-PET scans before laryngectomy. HE-sections were obtained from the surgical specimen and tumor was delineated (tumor(HE)). The GTVs on CT and MRI were delineated in consensus. PET-based GTVs were automatically segmented. The three-dimensionally reconstructed specimen was registered to the various images. Modality-specific CTV margins were derived and added to the GTVs to achieve adequate tumor coverage. The resulting CTVs were compared with each other, to tumor(HE), and to CTV(CT10) constructed on CT with the clinical margin of 10mm. RESULTS: CTV margins of 4.3mm (CT), 6.1mm (MRI) and 5.2mm (PET) were needed to achieve adequate tumor coverage. The median volumes of the resulting modality-specific CTVs were 44ml (CT), 48ml (MRI) and 39ml (PET), while the CTV(10mm) was 80ml. CONCLUSION: For laryngohypopharyngeal tumors, 45-52% target volume reduction compared with CTV(10mm) is achievable when modality-specific CTV margins are used. PET-based CTVs were significantly smaller compared to CT- and MRI-based CTVs.