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Abstract: Introduction: The aim of this study is to assess the geometric accuracy of diffusion weighted (DW)-MRI by quantification of geometric distortions in the gross tumor volume (GTV) in head and neck (HN) cancer. Materials & Methods: A retrospective analysis was performed on the data of 23 patients (with 24 lesions). For these patients, magnetic field maps and DW-MRI were acquired. The magnetic field maps were converted to voxel displacement maps. GTV delineations were transferred onto these voxel displacement maps and the voxel shifts in the GTV were analyzed. Results: The median shift was 3.2mm and the maximal posterior and anterior shifts were up to 15.0 and 26.0mm respectively. The range of shifts varied from 11.8 to 25.6mm. The percentage of GTV voxels that showed a shift of at least 6mm was found to be 23.2%. Conclusions: Current DW-MRI images of HN tumors show severe distortions up to centimeters, which restrict the use of DW-MRI scans for GTV definition in RT treatment planning. [Copyright &y& Elsevier]

Abstract: Purpose: We investigated radiation-induced changes in the salivary glands, 6weeks after RT, using MRI. Materials and methods: Eighteen oropharyngeal cancer patients were treated with salivary gland sparing IMRT. All patients received a 3T MRI exam before and 6weeks after the end of RT, including a T1-weighted (T1w), a T2-weighted (T2w), and a dynamic contrast-enhanced (DCE) MRI. For both time points separately, the parotid and submandibular glands were delineated on the MR images. Differences in median signal intensity and signal variation within the glands were tested for significance. Correlations were studied between the MR changes and the planned RT dose. Results: The volume of the glands reduced significantly by 25%. The T1w signal decreased by 10% and the T2w signal increased by 23%. The k ep value decreased, while the v e increased. A correlation of the changes in T2w signal with the mean dose was found in both glands. Conclusions: Overall radiation-induced changes and volume loss were observed in the parotid and submandibular gland using MR. The observed differences indicated an increased water content such as found in oedema. The overall changes could be related to the mean dose, with a slightly greater impact in the high dose area. [Copyright &y& Elsevier]

• GTV delineations based on anatomical MRI overestimated the tumor volume by 95% • Geometrically accurate DW-MRI increases tumor delineation accuracy. • DW-MRI reduces the CTV volumes, while maintaining high tumor coverage. 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. [ABSTRACT FROM AUTHOR]

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 10 mm. Results CTV margins of 4.3 mm (CT), 6.1 mm (MRI) and 5.2 mm (PET) were needed to achieve adequate tumor coverage. The median volumes of the resulting modality-specific CTVs were 44 ml (CT), 48 ml (MRI) and 39 ml (PET), while the CTV 10mm was 80 ml. 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. [ABSTRACT FROM AUTHOR]

Background While surgery remains the cornerstone of rectal cancer treatment, organ-preservation is upcoming. Therefore, neo-adjuvant treatment should be optimized. By escalating doses, response can be increased. To limit toxicity of boost, accurate gross tumor volume (GTV) definition is required. MRI, especially undeformed fast spin echo diffusion-weighted MRI (DWI), looks promising for delineation. However, inconsistencies between observers should be quantified before clinical implementation. We aim to find which MRI sequence (T2w, DWI or combination) is optimal and clinically useful for GTV definition by evaluating inter-observer agreement. Methods Locally advanced rectal cancer patients (tumors <10 cm from anal verge) were scanned on 3T MRI transverse T2w and DWI ( b = 800 s/mm 2 ). Three independent observers delineated T2w, DWI and combination (Combi) after training-set. Volumes, conformity index (CI), and maximum Hausdorff distance (HD) were calculated between any observer-pair per patient per modality. Results Twenty-four consecutive patients were included. One patient had cT2 (4.2%), 19 cT3 (79.1%) and 4 cT4 (16.7%), with 2 clinical node negative (8.3%), 4 cN1 (16.7%), and 18 cN2 (75.0%) on MRI. From 24 patients, 70 sequences were available (24x T2, 23x DWI, and 23x Combi). Between observers, no significant volume differences were observed per modality. T2 showed significantly largest volumes compared to DWI (mean difference 19.85 ml, SD 17.42, p < 0.0001) and Combi (mean difference 7.16 ml, SD 11.58, p < 0.0001). Mean CI was 0.70, 0.71 and 0.69 for T2, DWI and Combi respectively ( p > 0.61). Average HD was largest on T2 (18.60 mm, max 31.40 mm, min 9.20 mm). Discussion Delineation on DWI resulted in delineation of the smallest volumes with similar consistency and mean distances, but with slightly lower Hausdorff distances compared to T2 and Combi. However, with lack of a gold standard it remains difficult to establish if delineations also represent true tumor. Study strengths were DWI adaptation to exclude geometrical distortions and training-set. DWI shows great potential for delineation purposes as long as sufficient experience exists and geometrical distortions are eliminated. [ABSTRACT FROM AUTHOR]