Title: MR Based Tumor Delineation for Lung Cancer Radiation Therapy Planning
Abstract: Magnetic resonance imaging provides excellent soft tissue contrast and higher image resolution than PET, but has seen limited use in target definition for lung cancer radiation therapy. In this study, we test the feasibility of MR-based contouring by comparing interobserver contouring variability on MRI to the current standard of CT and PET-CT. Nine patients with locally advanced lung cancer underwent T1 weighted 1.5T MRI (Volumetric Interpolated Breath-hold Examination – VIBE), diffusion weighted MRI (DW-MRI), CT, and PET-CT scans prior to radiation therapy. Seven of 9 patients had findings of atelectasis or pneumonia associated with their tumors; MRIs were acquired using expiration breath-hold for VIBE and respiratory navigation for DW-MRs. Following detailed contouring instructions, 2 radiologists, and 5 radiation oncologists delineated the lung tumor on the following protocols: 1) CT images without PET (CT); 2) CT images rigidly registered to PET-CT (CT/PET); and 3) morphological VIBE images rigidly registered to functional DW-MRI (MRI). Overlap fractions (OFs) were calculated as the intersection over union of physician volumes for each scan and protocol. Additionally, the contour boundaries were measured in 6 cardinal directions and the local standard deviation (local SD) was computed as the SD across all observers for each boundary. Overall standard deviation was computed as the mean of all local SDs for each scenario and used as a spatial measure of interobserver variability. Mean of ± standard deviation of CT, CT/PET, and MRI were 0.38 ± 0.14, 0.36 ± 0.12, and 0.32 ± 0.14, respectively. Differences between the three contouring sessions were not significant. Union volumes on CT (262 ± 226 cm3) were larger than CT/PET (169 ± 125 cm3, P = .02), and larger than MRI (226 ± 169.6 cm3, P = .17). Differences between CT/PET and MRI were borderline significant (P = .05). Intersection volumes on CT were larger than CT/PET (105.29 ± 98.5 cm3 vs 65.3 ± 61 cm3, P = .03) and MRI (66.87 ± 57.74 cm3, P = .09). Intersection volumes on CT/PET and MRI were comparable (P = .43). In contour boundary analysis, paired t-test did not show significant difference in overall SD between CT/PET and MRI (P = .19), and between CT/PET and CT (P = .27). An MRI-based delineation protocol showed similar, although slightly higher, spatial, and volumetric interobserver variability as a standard CT/PET based protocol. Further training may be required to reduce the level of interobserver variability for the MR-based protocol to that of CT/PET.
Publication Year: 2015
Publication Date: 2015-10-17
Language: en
Type: article
Indexed In: ['crossref']
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