A comparison of Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) for breast target volume delineation in prone and supine positions

Publication date: Available online 11 August 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Elise M. Pogson, Geoff P. Delaney, Verity Ahern, Miriam Boxer, Christine Chan, Steven David, Marion Dimigen, Jennifer A. Harvey, Eng-Siew Koh, Karen Lim, George Papadatos, Mei L. Yap, Vikneswary Batumalai, Elizabeth Lazarus, Kylie Dundas, Jesmin Shafiq, Gary Liney, Catherine Moran, Peter Metcalfe, Lois Holloway
Purpose/Objective(s)MRI provides no ionizing radiation dose (allowing inter and intra fraction imaging), improved soft tissue contrast and potentially improved conformity in delineation than CT. This study aimed to determine if T2 weighted magnetic resonance imaging improves seroma cavity (SC) and Whole Breast (WB) inter-observer conformity for radiotherapy purposes compared with the gold standard of CT, both in the prone and supine positions.Methods and MaterialsEleven observers (two Radiologists and nine Radiation Oncologists) delineated SC and WB Clinical Target Volumes (CTVs) on T2-weighted MRI and CT supine and prone scans (4 scans per patient) for 33 patient datasets. Individual observer's volumes were compared using the Dice Similarity Coefficient (DSC), Volume overlap Index (VOI), Centre of Mass (COM) shift and Hausdorff Distances (HD). An average Cavity Visualization Score (CVS) was also determined.ResultsImaging modality did not affect inter-observer variation for WB CTVs. Prone WB CTVs were larger in volume and more conformal than Supine CTVs (on both MRI and CT). SC volumes were larger on CT than MRI. SC volumes proved to be comparable in inter-observer conformity in both modalities (VOI of 0.57±0.03 for CT supine, 0.52±0.04 for MR supine, 0.56±0.03 for CT prone and 0.55±0.04 for MR prone) however after registering modalities together the inter-modality variation (DSC of 0.41±0.05 for supine and 0.38±0.04 for prone) was larger than the inter-observer variability for SC despite the location typically remaining constant.ConclusionsMRI inter-observer variation was comparable to CT for the WB CTV and SC delineation, in both prone and supine positions. Whilst the CVS and inter-observer concordance was not significantly higher for MRI than CT, the SCs were smaller on MRI, potentially due to clearer SC definition, especially on T2-weighted MR images.

Teaser

Inter-observer variation and volume differences in seroma cavity (SC) and Whole Breast (WB) Clinical Target Volumes (CTVs) from MRI and CT images, in prone and supine positions, were compared. Prone WB CTVs were larger and exhibited less inter-observer variation than supine in both imaging modalities. CT SC volumes were significantly larger than MRI in both positions. No clinically significant differences in inter-observer variation were demonstrated between MRI and CT for WB or SC volumes.


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