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M. De Ruiter



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    MINI 37 - SCLC Therapy (ID 165)

    • Event: WCLC 2015
    • Type: Mini Oral
    • Track: Small Cell Lung Cancer
    • Presentations: 1
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      MINI37.11 - Inter-Observer Variability in Hippocampus Delineation on MRI Scans for Hippocampal Avoidance Prophylactic Cranial Irradiation Trial (ID 2620)

      19:30 - 19:35  |  Author(s): M. De Ruiter

      • Abstract
      • Presentation
      • Slides

      Background:
      Prophylactic cranial irradiation (PCI) is the standard treatment in patients with small-cell lung cancer (SCLC) without progression after chemo-radiotherapy in stage I-III disease and after having a remission after chemotherapy in stage IV. In an international phase III trial (NCT01780675), patients with SCLC are randomised to receive PCI with or without Hippocampal Avoidance (HA). Accurate delineation of the hippocampus is crucial for this trial. In this study we evaluate the hippocampus delineation variability among radiation oncologists in multi-institutions for SCLC patients.

      Methods:
      The left and right hippocampus from 5 randomly selected patients (10 structures) were delineated by 5 radiation oncologists and 2 neuroradiologist in 7 institutions according to the RTOG atlas (http://www.rtog.org/CoreLab/ContouringAtlases/HippocampalSparing.aspx), together with a questionnaire. For each patient, a high resolution 3D inversion recovery T1 weighted MRI-scan was first registered to the planning CT-scan (1mm slicing). The observer then delineated the hippocampus according to the atlas on axial slices of the MRI. The mapped delineations on the CT were then used in dose planning with a 5mm margin. The mean and standard deviation (SD) of 1) volume and 2) range in medio-lateral, superior-inferior and anterior-posterior directions were computed for each structure. The corresponding inter-observer reliability was estimated by the intra-class correlation coefficient (ICC absolute agreement) using a linear mixed model. A median surface was computed and the overall delineation variability per structure was calculated by the root-mean-square (rms) of the local SD per sampled points on the median surface, while the local SD corresponds to the perpendicular distance between each observer and a sampled point.

      Results:
      The standard deviation of the delineated volume per structure varied from 0.14 to 0.48cm3. The corresponding inter-observer reliability (ICC) was 0.19, implying a high variability among the observers. The overall delineation variability per structure varied from 0.6 to 1.0mm. Areas with good agreements were the superior and inferior part of the hippocampus. The difficult area (Fig.1) was in the anterior medial area, close to the amygdala and uncus. The ICC in medio-lateral, superior-inferior and anterior-posterior directions were 0.55, 0.64 and 0.80, respectively. A large spread of the SD of range in medio-lateral direction and the relative low ICC imply that a better instruction, or training is desirable to improve the delineations. Figure 1



      Conclusion:
      There was a substantial variability in hippocampus delineation among the observers. Stricter adherence to the RTOG guidelines and (web-based) training are needed. The implication of the variations on the dose distribution is currently verified.

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