Abstract
PurposeTo assess how gross tumour volume (GTV) delineation in anal cancer is affected by interobserver variations between radiologists and radiation oncologists, expertise level, and use of T2-weighted MRI (T2W-MRI) vs. diffusion-weighted imaging (DWI), and to explore effects of DWI quality. Methods and materialsWe retrospectively analyzed the MRIs (T2W-MRI and b800-DWI) of 25 anal cancer patients. Four readers (Senior and Junior Radiologist; Senior and Junior Radiation Oncologist) independently delineated GTVs, first on T2W-MRI only and then on DWI (with reference to T2W-MRI). Maximum Tumour Diameter (MTD) was calculated from each GTV. Mean GTVs/MTDs were compared between readers and between T2W-MRI vs. DWI. Interobserver agreement was calculated as Intraclass Correlation Coefficient (ICC), Dice Similarity Coefficient (DSC) and Hausdorff Distance (HD). DWI image quality was assessed using a 5-point artefact scale. ResultsInterobserver agreement between radiologists vs. radiation oncologists and between junior vs. senior readers was good–excellent, with similar agreement for T2W-MRI and DWI (e.g. ICCs 0.72–0.94 for T2W-MRI and 0.68–0.89 for DWI). There was a trend towards smaller GTVs on DWI, but only for the radiologists (P = 0.03–0.07). Moderate-severe DWI-artefacts were observed in 11/25 (44%) cases. Agreement tended to be lower in these cases. ConclusionOverall interobserver agreement for anal cancer GTV delineation on MRI is good for both radiologists and radiation oncologists, regardless of experience level. Use of DWI did not improve agreement. DWI artefacts affecting GTV delineation occurred in almost half of the patients, which may severely limit the use of DWI for radiotherapy planning if no steps are undertaken to avoid them.
Highlights
To assess how gross tumour volume (GTV) delineation in anal cancer is affected by interobserver variations between radiologists and radiation oncologists, expertise level, and use of T2weighted Magnetic Resonance Imaging (MRI) (T2W-MRI) vs. diffusion-weighted imaging (DWI), and to explore effects of DWI quality
The mean GTVs and Maximum Tumour Diameter (MTD) measured on T2weighted MRI (T2W-MRI) by the Senior Radiologist and Senior Radiation Oncologist were smaller than those measured by the two junior readers on T2W-MRI (P < 0.01–0.02)
The results of this study show an overall good interobserver agreement for GTV delineation on MRI between radiologists and radiation oncologists, as well as between readers of different experience levels
Summary
To assess how gross tumour volume (GTV) delineation in anal cancer is affected by interobserver variations between radiologists and radiation oncologists, expertise level, and use of T2weighted MRI (T2W-MRI) vs. diffusion-weighted imaging (DWI), and to explore effects of DWI quality. Conclusion: Overall interobserver agreement for anal cancer GTV delineation on MRI is good for both radiologists and radiation oncologists, regardless of experience level. Introduced hybrid MR-linear accelerator (MRL) systems allow visualization of tumour changes during the course of treatment that can be used as input to adapt and optimize the treatment plan This offers new possibilities for boosting strategies targeting specific areas of residual tumour, provided that these areas can accurately be defined on MRI [6,7]. Tumour delineation on anatomical MRI requires detailed knowledge of cross-sectional image anatomy and morphology This can be challenging, in particular for less experienced readers. As anal squamous cell carcinomas are usually hypercellular, these tumours will typically show restricted diffusion and appear bright on DWI [10]
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