The Accuracy of registration of 18FDG PET-CT to radiotherapy planning CT for Non Small Cell Lung Cancer

  • Dr Mei Ling Yap, Radiation Oncology Department, Liverpool Hospital, Australia
  • Dr Shalini Vinod, Radiation Oncology Department, Liverpool Hospital, Australia
  • Dr Ivan Ho Shon, Department of Nuclear Medicine, Liverpool Hospital, Australia
  • Dr Allan Fowler, Radiation Oncology Department, Liverpool Hospital, Australia
  • Dr Michael Lin, Department of Nuclear Medicine and PET, Liverpool Hospital, Australia
  • Mr Gabriel Gabriel, Collaboration of Cancer Outcomes, Research and Evaluation (CCORE), Liverpool Hospital, Australia

    • Objective: Both locally and worldwide, the use of 18 Fluoro-de-oxy-2-glucose Positron Emission Tomography-Computed Tomography (18 FDG PET-CT) fusion in the radiotherapy planning process for non-small cell lung cancer (NSCLC) is becoming more prevalent. This study aims to compare the accuracy of registration of the CT component of the planning FDG PET-CT (pCT) and CT component of the diagnostic FDG PET-CT (dCT) to the radiotherapy planning CT (rCT) in patients with NSCLC.

    Methods: This prospective study included patients with stage I to III NSCLC. All underwent a radiotherapy planning CT scan, immediately followed by a FDG PET-CT scan in the radiotherapy treatment position. All patients had previously undergone a diagnostic FDG PET-CT at their original time of presentation. The dCT and pCT were registered to the rCT using a rigid body mutual information algorithm and minor manual adjustment performed. Four observers (2 radiation oncologists and 2 nuclear medicine physicians) identified a series of anatomical points on each scan and the differences in location were compared.

    Results: Preliminary analysis shows a smaller mean absolute error (MAE) at the carina point for pCT-rCT compared to dCT-rCT, 4.37 vs 5.73mm respectively (p=0.028). Comparison of other anatomical points reveal similar small differences. The MAE for all points is 4.11 vs 4.15 and root mean square error 4.40 vs 4.48 mm for pCt-rCT compared to dCT-rCT. Further results pending.

    Conclusions: From preliminary analysis, the registration of pCT to rCT appears to be more accurate than the registration of dCT to rCT, though the differences are small.