A two- year-old neutered Labrador dog was evaluated for acute onset hindlimb paresis and proprioceptive deficits. Spinal MRI revealed a lesion at the level of T9–T10, from which a presumptive diagnosis of spinal nephroblastoma was made. The dog showed clinical improvement after receiving neoadjuvant stereotactic radiotherapy but re-presented six  weeks later with neurological deterioration. In addition to the primary lesion, a repeat MRI study revealed lesions at T6–T7 and T12. The dog was euthanased and multiple intradural, extramedullary spinal cord lesions were found at postmortem examination. Histopathological analysis of the lesions confirmed spinal nephroblastoma. This report substantiates the likelihood of intraspinal metastases of nephroblastoma occurring in the dog.

In this prospective, exploratory study, we evaluated the positioning accuracy in a group of 15 dogs undergoing fractionated stereotactic radiotherapy for tumors affecting the head, using a modified human maxillary fixation device (Elekta Fraxion TM system). Positioning was assessed using on-board volumetric imaging, with a six-degrees-of-freedom image registration technique. Prior to treatment delivery, CBCT images were obtained and patient alignment was corrected, in both translational and rotational planes, using a six-degrees-of-freedom robotic patient positioning system (HexaPOD Evo RT System). The maximum angular inter-fraction motions observed were 6.1 • (yaw), 10.9 • (pitch), and 4.5 • (roll). The mean systematic translational errors were 4.7, 2.6, and 2.3 mm, mean random translational errors were 3.0, 2.2, and 2.5 mm, and mean overall translational errors were 2.4, 0.7, and 2.3 mm in the cranial-caudal, lateral, and dorsal-ventral directions, respectively. The mean systematic rotational errors were 1.17 • , 0.77 • , and 1.43 • , the mean rotational random errors were 1.65 • , 1.46 • , and 1.34 • and the mean overall rotational errors were 0.56 • , 0.22 • , and 0.29 • in the yaw, pitch, and roll directions, respectively. The mean error of the three-dimensional vector was 6.9 mm with a standard deviation of 3.8 mm. Ninety-five percent of the three-dimensional vectors were <14.8 mm. This study demonstrates that this maxillary fixation device relies on six-degrees-of-freedom registration and an ability to apply corrections using a six-degrees-of-freedom couch for accurate patient positioning and tumor targeting. Its use in conformal radiation therapy in dogs is not recommended. K E Y W O R D Sbrain tumor, nasal tumor, oncology, oral tumor, radiation therapy