A Multi-Center Contouring Study of Spinal Cord Comparing MRI and Myelo-CT Fusion

Abstract

Spine stereotactic body radiotherapy (SBRT) is an emerging treatment for patients with spinal metastases and is rapidly being adopted in the clinic. Spinal cord is the most important organs at risk in Spine SBRT. To contour spinal cord, MRI or Myelo-CT fusion are used. To date, the effects of the difference of the modality on contouring spinal cord have not been evaluated. A multi-center contouring study was performed to evaluate inter modality variations between 2 modalities. Nine radiation oncologists from 3 centers joined this study. A normal vertebra (case 1), a vertebra with Bilsky grade 1b-bone metastases (case 2) and a vertebra with Bilsky grade 3-bone metastases (case 3) were chosen. Plain CT, MRI and myelo-CT scans were performed on the vertebras. The images of MRI and myelo-CT were registered to plain CT by a radiation oncologist. Nine radiation oncologists contoured spinal cords on registered images independently. All registration and contouring were performed on a treatment planning system. To assess the difference of 2 modalities, inter observer variations between contours were evaluated with Dice similarity coefficient. Inter observer Dice similarity coefficients of case 1 on MRI and myelo CT, case 2 on MRI and myelo CT and case 3 on MRI and myelo CT were 0.820 ± 0.051 (Average ± SD), 0.869 ± 0.041, 0.830 ± 0.039, 0.883 ± 0.014, 0.858 ± 0.091 and 0.748 ± 0.066, respectively. (table) Inter observer variations on 2 modalities were evaluated. Variation was largest in contours with myelo CT on vertebra with Bilsky grade 3 metastases.