Stereotactic body radiation therapy for heart-base tumors in six dogs

Heart-base tumors are increasingly treated with radiotherapy, yet safety and efficacy are incompletely understood. This case series describes outcomes after stereotactic body radiation therapy (SBRT) for presumed chemodectoma. Six pet dogs. A retrospective study was performed, including dogs with a clinical diagnosis of chemodectoma and treatment with three-fraction SBRT (30 Gy total). Heart-base tumors, presumed or confirmed to be chemodectomas, were diagnosed via histopathology or imaging. Treatment was delivered with intensity modulation and cone-beam computed tomography–based image guidance, using a linear accelerator and robotic couchtop. Intrafraction respiratory motion was managed with either neuromuscular blockade and breath-holding (n = 3) or high-frequency jet ventilation (n = 3); mean total anesthesia times for each technique were 165 and 91 min per fraction, respectively. Four tumors were assessed after SBRT; tumor volume decreased by 30–76%. Possible treatment-related complications included cough, tachyarrhythmias, and congestive heart failure. Two dogs experienced sudden death 150 and 294 days after SBRT. Three dogs are alive 408–751 days after SBRT, and one dog died of unrelated disease 1,228 days after SBRT. This SBRT protocol resulted in rapid tumor volume reduction, and jet ventilation effectively reduced treatment delivery times. However, cardiac arrhythmias (presumably tumor or treatment associated) and sudden death were common after SBRT. Therefore, SBRT is a potentially useful treatment but may not be appropriate for dogs with incidentally diagnosed, slowly growing tumors, which are not causing cardiovascular disturbances. Longer follow-up and larger case numbers are needed to more completely define safety and impact of treatment on long-term survivability.