For laryngohypopharyngeal tumors, 45-52% target volume reduction compared with CTV is achievable when modality-specific CTV margins are used. PET-based CTVs were significantly smaller compared to CT- and MRI-based CTVs.

Background: Validation of magnetic resonance imaging (MRI) and development of guidelines for the delineation of the gross tumor volume (GTV) is of utmost importance to benefit from the visibility of anatomical details on MR images and to achieve an accurate GTV delineation. In the ideal situation, the GTV delineation corresponds to the histopathologically determined 'true tumor volume'. Consequently, we developed guidelines for GTV delineation of laryngeal and hypopharyngeal tumors on MRI and determined the accuracy of the resulting delineation of the tumor outline on histopathology as gold standard. Material and methods: Twenty-seven patients with T3 or T4 laryngeal/hypopharyngeal cancer underwent a MRI scan before laryngectomy. Hematoxylin and eosin sections were obtained from surgical specimens and tumor was delineated by one pathologist. GTV was delineated on MR images by three independent observers in two sessions. The first session (del1) was performed according to clinical practice. In the second session (del2) guidelines were used. The reconstructed specimen was registered to the MR images for comparison of the delineated GTVs to the tumor on histopathology. Volumes and overlap parameters were analyzed. A target margin needed to assure tumor coverage was determined. Results: The median GTVs (del1: 19.4 cm 3 , del2: 15.8 cm 3 ) were larger than the tumor volume on pathology (10.5 cm 3 ). Comparable target margins were needed for both delineation sessions to assure tumor coverage. By adding these margins to the GTVs, the target volumes for del1 (median: 81.3 cm 3 ) were significantly larger than for del2 (median: 64.2 cm 3 ) (p 0.0001) with similar tumor coverage. Conclusions: In clinical radiotherapy practice, the delineated GTV on MRI is twice as large as the tumor volume. Validated delineation guidelines lead to a significant decrease in the overestimation of the tumor volume.

background and purpose. To determine the spatial correspondence between the gross tumor volume (GTV) delineated on computer tomography (CT) and the actual tumor on histopathology. Material and methods. Sixteen patients with T3 or T4 laryngeal or hypopharyngeal cancer underwent a CT scan before total laryngectomy. The GTV was delineated on CT by three independent observers and by consensus between the three observers. After surgery, whole-mount hematoxylin-eosin stained (H&E) sections were obtained. One pathologist delineated the tumor in the H&E sections (tumor H&E ). The reconstructed specimen was registered to the CT scan in order to compare the GTV to the tumor H&E in three dimensions. The overlap between the GTV and the tumor H&E was calculated and the distance between the volumes was determined. results. Tumor tissue was delineated in 203 of 516 H&E sections. For 14 patients a detailed analysis could be performed. The GTV volume was on average 1.7 times larger than the volume of the tumor H&E . The mean coverage of the tumor H&E by the consensus GTV was 88%. Tumor H&E tissue was found at 1.6 mm to 12.9 mm distance outside the GTV depending on observer and patient. conclusions. GTVs delineated on CT for laryngeal and hypopharyngeal cancer were 1.7 times larger than the tumor. Complete coverage of the tumor by the GTV was, however, not obtained.

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In radiotherapy treatment planning, tumor delineation based on diffusion-weighted imaging (DWI) by magnetic resonance imaging (MRI) is a promising technique. MR-only-based target definition becomes important with the recent development of MRI integrated radiotherapy treatment modalities. In this case series, DWI-based gross tumor volume (GTV) was validated using pathology and compared with a clinical GTV based on computed tomography (CT) imaging and MRI.This case series includes three patients with a laryngeal tumor. Prior to total laryngectomy (TLE), imaging was performed on CT and MRI, including a DWI scan. After TLE, the surgical specimen was processed and cut into 3-mm thick slices. The tumor was delineated on hematoxylin-eosin (HE) stained sections by a pathologist (tumorHE). This pathological imaging, including the tumorHE delineation, was three-dimensionally reconstructed and registered to the imaging. The GTV was delineated by a radiation oncologist based on CT and MR imaging (GTVclinical) and semi-automatically delineated based on DWI (GTVDWI).The microscopic tumor extent outside the GTVDWI contour was 3.0 mm, 2.7 mm, and 11.3 mm for cases I, II, and III, respectively. The microscopic tumor extent outside the GTVclinical was 7.5 mm, 2.1 mm, and 1.5 mm for cases I, II, and III, respectively. The tumor, on histology, was covered by the GTVs for 80%, 74%, and 31% (GTVDWI) and 73%, 72%, and 89% (GTVclinical) for the three subsequent cases, respectively. The GTVDWI resembled the tumorHE more than the GTVclinical in case I and case II. In case III, GTVDWI missed the caudal part of the tumor that was included in the clinical delineation due to a lack of contrast and the heterogeneous signal intensity of the tumor in DWI.In this case series, we showed the potential of DWI for MR-guided radiotherapy treatment if a clear contrast is visible. DWI-based GTV delineation might be a fast alternative to manual delineation, which could speed up the on-table target definition using an MRI-linac system. A larger case series is needed to verify these results.