Abstract
IntroductionThe application of deformable image registration (DIR) to megavoltage computed tomography (MVCT) images benefits adaptive radiotherapy. This study aims to quantify the accuracy of DIR for MVCT images when using different deformation methods assessed in a cubic phantom and nasopharyngeal carcinoma (NPC) patients.MethodsIn the control studies, the DIR accuracy in air‐tissue and tissue‐tissue interface areas was observed using twelve shapes of acrylic and tissue‐equivalent material inserted in the phantom. In the clinical studies, the 1st and 20th fraction MVCT images of seven NPC patients were used to evaluate application of DIR. The eight DIR methods used in the DIRART software varied in (i) transformation framework (asymmetric or symmetric), (ii) DIR registration algorithm (Demons or Optical Flow) and (iii) mapping direction (forward or backward). The accuracy of the methods was compared using an intensity‐based criterion (correlation coefficient, CC) and volume‐based criterion (Dice's similarity coefficient, DSC).ResultsThe asymmetric transformation with Optical Flow showed the best performance for air‐tissue interface areas, with a mean CC and DSC of 0.97 ± 0.03 and 0.79 ± 0.11 respectively. The symmetric transformation with Optical Flow showed good agreement for tissue‐tissue interface areas with a CC of (0.99 ± 0.01) and DSC of (0.89 ± 0.03). The sequences of target domains were significantly different in tissue‐tissue interface areas.ConclusionsThe deformation method and interface area affected the accuracy of DIR. The validation techniques showed satisfactory volume matching of greater than 0.7 with DSC analysis. The methods can yield acceptable results for clinical applications.
Highlights
The application of deformable image registration (DIR) to megavoltage computed tomography (MVCT) images benefits adaptive radiotherapy
Journal of Medical Radiation Sciences published by John Wiley & Sons Australia, Ltd on behalf of Australian Society of Medical Imaging and Radiation Therapy and New Zealand Institute of Medical Radiation Technology
We are interested in answering the question “How well do the different DIR methods perform in tomotherapy MVCT images for nasopharyngeal carcinoma (NPC) patients?” This study aims to evaluate the accuracy of DIR on MVCT images of phantom and NPC patients using Deformable Image Registration and Adaptive Radiotherapy (DIRART) software and various (i) transformation frameworks, (ii) DIR registration algorithms and (iii) mapping directions
Summary
The application of deformable image registration (DIR) to megavoltage computed tomography (MVCT) images benefits adaptive radiotherapy. This study aims to quantify the accuracy of DIR for MVCT images when using different deformation methods assessed in a cubic phantom and nasopharyngeal carcinoma (NPC) patients. The 1st and 20th fraction MVCT images of seven NPC patients were used to evaluate application of DIR. Results: The asymmetric transformation with Optical Flow showed the best performance for air-tissue interface areas, with a mean CC and DSC of 0.97 Æ 0.03 and 0.79 Æ 0.11 respectively. The symmetric transformation with Optical Flow showed good agreement for tissue-tissue interface areas with a CC of (0.99 Æ 0.01) and DSC of (0.89 Æ 0.03).
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