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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]

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]