Author of

• 12544

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  P3.08 - Poster Session 3 - Radiotherapy (ID 199)

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

  • 12552

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    P3.08-008 - Comparison of auto- segmented PET volumes in discrete Lung tumors with CT based manual contours: Implications in radiotherapy planning. (ID 1075)

    09:30 - 09:30  |  Author(s): S.P. Giri
    • Abstract

    Background
    The aim of this study was to compare the GTV volumes drawn manually on CT scans with GTV delineation on FDG PET scans utilizing automatic threshold (SUV 3) and gradient-based (PET Edge) auto-segmentation methods in lung tumors and discuss implications in radiation planning.

    Methods
    Twenty two patients with lung carcinoma treated with radiation therapy having discrete lesions with no adjacent consolidation or atelectasis and having PET scan done within 30 days of simulation CT were enrolled in this study. FDG-PET/CT and planning CT were transferred to the MIM software and fused using the deformable registration algorithm. For each patient three GTV’s were defined. GTV CT manually contoured on CT scan using lung window in lesions adjacent to lung parenchyma and mediastinal window when adjacent to mediastinum or chest wall. For GTV SUV3, circle of interest was created with a margin around the lesion, excluding blood pool (heart) and auto segmented with SUV value of 3. GTV-PET Edge was auto segmented using PET Edge tool centered on the hyper metabolic area. Statistical Methods: Spearman correlation coefficients were constructed to view relationships between variables, and sign tests were used for inference.

    Results
    Among 22 patients, only one was small cell and 21 were with non-small cell carcinomas (8 squamous cell, 11 adenocarcinoma and 2 poorly differentiated). As per the AJCC 7[th] Ed, 16-stage I, 3 stage II and 3 belong to IIIA. Median CT volume for all lesions was 4.385, (range 0.68-173.74), PET Edge median 4.235 (range 0.474-113.00), SUVs 3 median 4.845 (0.659-109.1). Correlation between CT and SUV 3, SUV 3 and PET edge, CT and PET Edge were 0.8690, 0.9105 and 0.8585 respectively. No significant differences between CT and SUV 3 volumes (p=0.5235) as well as CT and PET Edge volumes (p=0.3833). But PET edge volumes were significantly less compared to SUV 3 volumes (p=0.0525).

    Conclusion
    Lobectomy is the treatment of choice for early stage non-small cell lung cancers. In medically inoperable patients stereotactic body radiation therapy has become the new standard of care with 3 year overall survival of 60%, similar to lobectomy. For conventional Radiation therapy GTV’s are expanded to generate CTV for presumed microscopic disease (CTV). In SBRT GTV and CTV are identical. In phantom studies auto segmentation using PET edge tool shown to be superior to other methods and better correlated with pathology. In our study the median volume by PET edge is smaller compared to other two modalities. The difference is statistically significant between PET edge and SUV 3 but not between CT and PET edge. Hence, adaptation of PET edge tool may decrease the GTV and PTV volumes that will enable to spare the normal structures better in SBRT. Surgical pathologic studies determined CTV margins of 6mm for squamous and 8mm for adeno, beyond gross pathological tumor (Giraud et al). CT overestimates GTV volume in lung tumors with no additional or negative margins required to create CTV (Chan et al). We allude that adaptation of SUV 3 may be enough to generate CTV volumes for conventional radiation therapy.