COMPARISON OF TWO COARSE FRACTIONATED RADIATION PROTOCOLS FOR THE MANAGEMENT OF CANINE PITUITARY MACROTUMOR: AN OBSERVATIONAL STUDY OF 24 DOGS.

Radiotherapy is a commonly used treatment for pituitary macrotumors in dogs, but the optimum protocol has not been established. Twenty four dogs with MRI confirmed pituitary macrotumors were treated with one of two radiotherapy protocols. Twelve dogs were treated with 10 fractions of 3.8 Gy/fraction on a "Monday-Wednesday-Friday" schedule, the remaining 12 with five "once-a-week" protocols (1 × 5 Gy, followed by 4 × 8.25 Gy) to a total dose of 38 Gy. The overall median survival time for all dogs was 235 days (range 28-1,328), dogs treated with 10 fractions had a median survival time of 961 days (range 28-1,328) compared to 182 days (range 42-507) in the five-fraction group (P = 0.006). Clinical improvement was found in both groups, and no significant side effects were noted in either group. These results suggest that a "Monday-Wednesday-Friday" schedule may improve survival times, as compared to a "once-a-week" protocol. As this study was of an observational nonrandomized nature, future work is necessary to establish whether more highly fractionated protocols or different total doses will further improve outcome.