Long-term outcomes with conventional fractionated and stereotactic radiotherapy for suspected heart-base tumours in dogs.

Published radiotherapy results for suspected heart-based tumours in dogs are limited. In this retrospective longitudinal study (3/2014-2019), eight dogs with either clinical signs attributable to a heart-base mass (6), or asymptomatic with a progressively larger mass on echocardiogram (2), received conventional fractionated radiotherapy (CFRT) or stereotactic body radiotherapy (SBRT). Clinical findings in symptomatic cases included one or more of the following: retching/coughing (4), exercise intolerance (2), collapse (1), pericardial effusion (2), rare ventricular premature contractions (2), abdominal effusion (1), or respiratory distress due to chylothorax (1). CFRT cases received 50 Gray (Gy) in 20 fractions and SBRT cases received 30 Gy in 5 or 24 Gy in three fractions. Two dogs received chemotherapy post-radiation. At analysis, 7/8 dogs were deceased and one was alive 684 days post-treatment. The estimated median overall survival (MOS) from first treatment was 785 days (95% CI 114-868 days, [range 114-1492 days]). Five dogs received CFRT (MOS 817 days; (95% CI 155 days-not reached [range 155-1492 days])). Three dogs received SBRT with one alive at analysis (MOS 414 days, (95% CI, 114 days-not reached [range 114-414 days])). No statistically significant difference was found between survival for CFRT and SBRT. Of the symptomatic patients, 5/6 showed improvement. Mass size reduced in 4/5 cases receiving follow-up ultrasounds. Possible complications included asymptomatic radiation pneumonitis (4), atrial tachycardia/premature beats (4) and pericardial effusion with heart failure coincident with tumour progression (1). This study provides preliminary evidence that radiotherapy may impact clinically relevant or progressively enlarging heart-base masses.