A Comparative Evaluation of 3 Different Free-Form Deformable Image Registration and Contour Propagation Methods for Head and Neck MRI: The Case of Parotid Changes During Radiotherapy.
To validate and compare the deformable image registration and parotid contour propagation process for head and neck magnetic resonance imaging in patients treated with radiotherapy using 3 different approaches-the commercial MIM, the open-source Elastix software, and an optimized version of it.



Twelve patients with head and neck cancer previously treated with radiotherapy were considered. Deformable image registration and parotid contour propagation were evaluated by considering the magnetic resonance images acquired before and after the end of the treatment. Deformable image registration, based on free-form deformation method, and contour propagation available on MIM were compared to Elastix. Two different contour propagation approaches were implemented for Elastix software, a conventional one (DIR_Trx) and an optimized homemade version, based on mesh deformation (DIR_Mesh). The accuracy of these 3 approaches was estimated by comparing propagated to manual contours in terms of average symmetric distance, maximum symmetric distance, Dice similarity coefficient, sensitivity, and inclusiveness.



A good agreement was generally found between the manual contours and the propagated ones, without differences among the 3 methods; in few critical cases with complex deformations, DIR_Mesh proved to be more accurate, having the lowest values of average symmetric distance and maximum symmetric distance and the highest value of Dice similarity coefficient, although nonsignificant. The average propagation errors with respect to the reference contours are lower than the voxel diagonal (2 mm), and Dice similarity coefficient is around 0.8 for all 3 methods.



The 3 free-form deformation approaches were not significantly different in terms of deformable image registration accuracy and can be safely adopted for the registration and parotid contour propagation during radiotherapy on magnetic resonance imaging. More optimized approaches (as DIR_Mesh) could be preferable for critical deformations.
1 Medical Physics Department, San Raffaele Scientific Institute, Milan, Italy.
Sara
S
Broggi
2 Institute of Molecular Bioimaging and Physiology (IBFM), CNR, Segrate, Milan, Italy.
Elisa
E
Scalco
1 Medical Physics Department, San Raffaele Scientific Institute, Milan, Italy.
Maria Luisa
ML
Belli
3 IBiTech-bioMMeda, University of Ghent, Ghent, Belgium.
Gerlinde
G
Logghe
4 Vrije Universiteit Brussel, Brussels, Belgium.|5 GZA Sint Augustinus - Iridium Kankernetwerk Antwerpen, Antwerp, Belgium.
Dirk
D
Verellen
2 Institute of Molecular Bioimaging and Physiology (IBFM), CNR, Segrate, Milan, Italy.
Stefano
S
Moriconi
6 Radiotherapy Department, San Raffaele Scientific Institute, Milan, Italy.
Anna
A
Chiara
7 Clinical and Experimental Radiology, Experimental Imaging Center, San Raffaele Scientific Institute, Milan, Italy.
Anna
A
Palmisano
7 Clinical and Experimental Radiology, Experimental Imaging Center, San Raffaele Scientific Institute, Milan, Italy.
Renata
R
Mellone
1 Medical Physics Department, San Raffaele Scientific Institute, Milan, Italy.
Claudio
C
Fiorino
2 Institute of Molecular Bioimaging and Physiology (IBFM), CNR, Segrate, Milan, Italy.
Giovanna
G
Rizzo
D000465:Algorithms; D054893:Cone-Beam Computed Tomography; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D010306:Parotid Gland / Q000000981:diagnostic imaging / Q000473:pathology; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012984:Software
Elastix; MIM; accuracy evaluation; contour propagation; head and neck MRI; image registration