Introduction

Canine nasal tumors are locally invasive, with stage IV disease including cribriform plate lysis and potentially intracalvarial involvement. Computed tomography (CT) is used to help create conformal plans, as electron density allows for dosimetric prediction in radiation planning. CT alone may not provide the soft tissue contrast needed to discern normal brain from tumor tissue in stage IV patients. Magnetic resonance imaging (MRI) can provide additional soft tissue contrast to aid in contouring for radiation planning. The objective of this study was to assess the use of either CT or CT and MRI for guiding tumor delineation in canine stage IV nasal tumor patients.

Methods

For each patient, gross tumor volume (GTV) was contoured with CT and again with CT-MRI co-registered images at least one week later to decrease bias between the two data sets. GTV differences were assessed for normality and a non-parametric Wilcoxon matched pairs test was used to assess for statistical significance.

Results

Forty-three patients with 44 image sets were included. Forty-one image sets included stage IVb disease. The median size of the GTV contoured from the CT was 47.55 cc. The median size of GTV contoured with the CT co-registered to the MRI was 50.65 cc. Median tumor volumes were significantly larger for MRI co-registered image sets (p=0.0047, 95% CI 0.2–1.6). The median percent difference between the two groups was 1.86%.

Conclusion

MRI may provide more accurate clinical delineation of tumor volumes in stage IV canine nasal tumors, with larger GTV volumes obtained with MRI co-registration.

Funding Information

Not applicable.