Affiliation:
1. Animal Clinic Hofheim
2. Diagnostic Imaging Department for Companion Animals and Horses,
University of Veterinary Medicine Vienna (Vetmeduni Vienna)
3. Clinic of Small Animal Surgery and Reproduction, Ludwig-Maximilian
University
4. Freelance Radiologist
5. Anicura Animal Oncology and Imaging Center
Abstract
Abstract
Introduction Volume definition is a delicate step within the radiation
treatment planning process and the precision of defining the volumes to
irradiate is important for the success of the radiation treatment.
Traditionally, radiation plans are created using computed tomography (CT)
studies. Due to its different mechanism of action, magnetic resonance imaging
(MRI) is more sensitive for detection of brain lesions. Therefore, using fused
images of both imaging modalities should result in a more precise definition of
the volumes to irradiate. The feasibility to fuse CT and MRI studies performed
at different institutions was tested to subsequently analyse the influence of
the fused images on target volume definition.
Materials and methods Fourteen dogs and four cats with brain lesions
having MR- and CT-imaging were included. Contrast-enhanced radiotherapy planning
CT scans were fused to T1-weighted post-contrast and T2-weighted MRI scans. The
gross tumor volume (GTV), the clinical tumor volume (CTV) and the planning
target volume (PTV) were delineated on CT- and MRI studies. CT and MRI volumes
were compared with regard to volumetric and spatial differences.
Results The mean GTV was larger on MRI than on CT (2.15 vs.1.54
cm3). Also the mean CTV was larger on MRI than on CT (5.34 vs.
4.38 cm3). Consequently, the mean PTV was larger on MRI than on CT
(14.20 vs. 10.82 cm3) as well. None of the differences in defined
volumes were significant. Fusion images were accepted showing mean errors of
1.32 mm (mean error) and 1.73 mm (maximal error).
Conclusion CT-MRI fusion was feasible especially when defined, reliable,
and consistent anatomic landmarks were used as registration points. Volumetric
differences between CT and MRI were insignificant. In general, GTV and CTV were
easier identified on MRI.
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