Incorporating Hypofractionated Radiotherapy Improves Management of Canine Urothelial Carcinoma: A Retrospective Study.

This retrospective study evaluated a novel hypofractionated radiation therapy (RT) protocol for canine urothelial carcinoma (UC). Medical records of dogs diagnosed with UC and treated were retrospectively reviewed. Inclusion criteria included diagnosis of UC, treatment with hypofractionated RT, absence of prostatic involvement or metastatic disease, and adequate follow-up. The RT protocol consisted of 25 Gy delivered to the planning target volume (PTV) in five fractions on an every-other-day schedule. Dynamic adaptive radiation therapy (DART) was used in select bladder tumors to minimize geographic miss. Data on adverse events, clinical response, adjuvant therapies, and prognostic factors were evaluated in relation to progression-free survival (PFS) and overall survival (OS). Eighteen dogs met the inclusion criteria. All received nonsteroidal anti-inflammatory drugs (NSAIDs), and 67% also received chemotherapy after RT. Tumor location included bladder only (55%), urethra only (28%), or both (17%). RT was well tolerated, with only low-grade gastrointestinal (17%) or urinary (6%) adverse events observed. Measurable tumor response was observed in 82% (14/17) with follow-up imaging. Median PFS was 394 days (95% CI: 169-619), and median OS was 565 days (95% CI: 497-632). Dogs with urethral involvement demonstrated a shorter PFS compared to those without (median = 182 vs. 457 days, respectively [p = 0.02]). Chemotherapy did not impact PFS or OS. The novel hypofractionated RT protocol was well tolerated alone and in combination with other treatments. Tumor responses and survival times were improved compared to historical data on dogs receiving NSAIDs and/or chemotherapy alone.