A retrospective analysis of stereotactic body radiation therapy for canine heart base tumors: 26 cases

This study retrospectively evaluated outcomes and adverse radiation effects (AREs) associated with stereotactic body radiation therapy (SBRT) for canine heart base tumors (HBTs). A secondary aim was to identify any demographic or echocardiographic factors that might determine which dogs would most benefit from SBRT. Twenty-six dogs that received SBRT for an imaging-based diagnosis of a HBT were evaluated. Twenty-three dogs were treated with three fractions of 10 Gy delivered daily or every other day. The remaining 3 dogs received variable protocols of one to five fractions. Demographic, echocardiographic, and radiographic information, AREs, and treatment responses were collected. Correlations of these data with survival time were evaluated. The median overall survival time was 404 days (95% confidence interval: 239–554 days). The majority of dogs experienced a partial response (25%) or stable disease (60%) for a median duration of 333 days (95% confidence interval: 94–526 days). Three dogs had progressive disease within six months of SBRT. Radiographic pneumonitis was identified in 7 of 23 dogs, and clinical pneumonitis was identified in 4 dogs. No other AREs were noted. The rate of distant metastasis was 13%. On multivariate analysis, it was found that vena caval obstruction, supraventricular and ventricular arrhythmias, clinical signs, and enlarged locoregional lymph nodes at presentation were negatively associated with survival time. Stereotactic body radiation therapy was delivered with a low rate and degree of normal tissue complications. Asymptomatic dogs with confirmed, progressive growth of a HBT may most likely benefit from SBRT.