A combined protocol with piroxicam, chemotherapy and whole pelvic irradiation with simultaneous boost volumetric modulated arc radiotherapy for muscle-invasive canine urinary transitional cell carcinoma: first clinical experiences

The aims of this pilot study were to evaluate the feasibility and efficacy of high-dose hypo-fractionated volumetric modulated arc radiotherapy (VMAT) applied to the whole pelvic region radiotherapy (WPRT) with multilevel simultaneous integrated boost (MLSIB) combined with piroxicam and chemotherapy in canine transitional cell carcinoma (TCC) of the lower urinary tract with muscle invasion transitional cell carcinoma (TCC). Twelve dogs were enrolled, according to stage, in two groups: group 1, TCC confined to the urinary tract; group 2, TCC with metastasis. The planning target volume (PTV-tumor) dose was tailored from 36 to 42 Gy in 6 fractions. All dogs were prescribed piroxicam and radiosensitizing carboplatin and six received chemotherapy after radiotherapy. Serial follow-up with computed tomography (CT) and magnetic resonance imaging (MRI) examinations was performed. Disease control and toxicity effects were evaluated according to the Response Evaluation Criteria in Solid Tumor (RECIST) and Veterinary Radiation Therapy Oncology Group (VRTOG) criteria. The treatment was well tolerated, and no high-grade side effects were reported. The median overall survival times for group 1 and group 2 were 1,230 days and 150 days, respectively. A considerable percentage of patients in group 1 (50%) was still alive at the time of writing, and a longer follow-up could enable a more accurate survival analysis. This preliminary analysis showed that VMAT applied to the WPRT with MLSIB is an effective and safe option for dogs suffering from lower urinary TCC although the presence of metastases worsens the prognosis.