Author of

• 11645

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  P2.08 - Poster Session 2 - Radiotherapy (ID 198)

  • Event: WCLC 2013
  • Type: Poster Session
  • Track: Radiation Oncology + Radiotherapy
  • Presentations: 1
  • Moderators:
  • Coordinates: 10/29/2013, 09:30 - 16:30, Exhibit Hall, Ground Level

  • 11653

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    P2.08-008 - A prospective study to determine inter-observer variability of Gross Tumor Volume with FDG-PET/CT compared to CT alone in Stage III Non-Small Cell Lung Cancer using Three-dimensional Analysis. (ID 1086)

    09:30 - 09:30  |  Author(s): R. Rivest
    • Abstract

    Background
    There are no randomized trials comparing CT versus FDG-PET/CT based radiotherapy planning for lung cancer or any other disease site.Based on phase II studies, a convincing body of data has emerged within the last 10 years incorporating the use of FDG-PET scans for radiotherapy planning in lung cancer.Published data comparing changes in volume measured with FDG-PET/CT to CT alone indicates that the magnitude of treatment volume changes with incorporation of PET in radiotherapy planning for lung cancer varies from 27% - 100%. However, volumetric data only provides information on changes in size and does not account for potential changes in position and shape of the target, thereby affecting variability of the GTV in NSCLC. In this study we describe influence of FDG-PET/CT or CT alone for the primary and mediastinal nodal disease in radiation planning for stage III NSCLC in relation to changes in volume, position and overlap of the GTV. We also report the interobserver variability between radiation oncologists for FDG-PET/CT and CT alone-derived GTV. In addition to volumetric measurements, we have used a vector displacement method for three-dimensional (3D) positional analysis. We have further evaluated the overlap of the primary and nodal GTV with Dice Similarity Coefficient (DSC) method

    Methods
    Patients (n=29) underwent Three Dimensional Conformal Radiotherapy (3DCRT) planning by three different radiation oncologists. Simultaneous co-registered CT and FDG-PET/CT were obtained in the same treatment planning position. Gross Tumor Volume (GTV) for lung tumor and mediastinal lymphadenopathy was contoured and compared for changes in volume and position. Interobserver variability was determined using three-dimensional analysis with vector displacement and the Dice Similarity Coefficient (DSC). Concordance for the number of lymph nodes contoured was performed.

    Results
    Mean GTV for lung tumor with FDG-PET/CT and CT alone was 62.0 cm[3] and 74.64 cm[3], respectively (p=0.0005), resulting in a 17% reduction by FDG-PET/CT. Mean GTV for mediastinal lymphadenopathy was 15.72 cm[3] and 19.02 cm[3] (p=0.084), equalling a 17% reduction GTV for FDG-PET/CT. Mean vector displacement of lung tumor was 2.0 mm with FDG-PET/CT versus 7.1 mm with CT alone (p = 0.0016), equating to a 3.6 fold reduction in interobserver variability of position. Mean vector displacement of the mediastinal lymphadenopathy was 1.53 mm with FDG-PET versus 10.2 mm for CT alone (p= 0.0005), resulting in a 6.7 fold reduction in interobserver variability. Median Dice Similarity Coefficient (DSC) for the primary GTV contours was 0.87 for FDG-PET/CT and 0.74 for CT alone. For the nodal GTV DSC were 0.79 and 0.59, respectively. Physician agreement on the number of lymph nodes contoured was 15/29 on CT and 27/29 patients for FDG-PET/CT. Only two of the three physicians agreed on the number of lymph nodes contoured for CT alone in 12/29 versus only 2/29 patients for FDG-PET/CT (p=0.0018).

    Conclusion
    FDG-PET/CT significantly reduces mean lung tumor and mediastinal nodal GTV, is more precise for size and position in defining target volumes, and reduces interobserver variability. There was greater agreement for the number of lymph nodes contoured on FDG-PET/CT compared to CT alone.