Patterns of local residual disease and local failure after intensity modulated/image guided radiation therapy for sinonasal tumors in dogs.

Background: Most dogs with sinonasal tumors (SNT) treated with radiation therapy (RT) died because of local disease progression.

Hypothesis/objectives: Our hypothesis is that the majority of local failure and residual disease would occur within the radiation field.

Animals: Twenty-two dogs with SNT treated with RT.

Methods: Retrospective cohort study.

Inclusion Criteria: dogs with SNT receiving 10 daily fractions of 4.2 Gy with intensity modulated radiation therapy (IMRT)/image guided radiation therapy (IGRT) and follow-up cone beam computed tomography (CBCT). Each CBCT was registered with the original radiation planning CT and the gross tumor volume (GTV) contoured. The GTV was classified as residual (GTVr) or a failure (GTVf). The dose statistic for each GTV was calculated with the original IMRT plan. For GTVf, failures were classified as "in-field," "marginal," or "out-field" if at least 95, 20-95, or less than 20% of the volume of failure was within 95% (D95) of the total prescription dose, respectively.

Results: There were 52 follow-up CBCT/CTs. Overall there was a GTVr for 20 dogs and GTVf for 16 dogs. The majority of GTVr volume was within the original GTV. GTVf analysis showed that 75% (12/16) were "in-field," 19% (3/16) were "marginal" and 6% (1/16) were "out-field."

Conclusion And Clinical Importance: In-field failures are the main pattern for local recurrence, and there is evidence of radioresistant subvolumes within the GTV.