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Radiation treatment planning is performed on images that do not take variation in patient position into account. To compensate for expected variations in position of the patient, a three-dimensional expansion of the clinical target volume, or set-up margin, is added. Variations in patient position can be decreased through use of an immobilization device, allowing selection of a smaller set-up margin. The objective of this prospective study was comparison of interfractional variation in patient position between set-ups of the canine head region using palpation of bony landmarks and set-ups using a head-repositioning device. Fiducial markers were attached to the skull bones of three research dogs, and the dogs were positioned as for a typical radiation treatment of the head region using both set-up methods. A kilovoltage on-board imager was used to acquire orthogonal images and the difference between the x-, y-, and z-axis coordinates of each fiducial marker relative to the initial reference isocenter was measured. The difference in patient position for each axis coordinate was significantly lower for set-ups using the head-repositioning device than for set-ups using bony landmarks (P < 0.05). Ninety-five percent of the absolute values of the displacement vector differences were < 4.62 mm for set-up using bony landmarks, and < 1.93 mm for set-up using the head-repositioning device. A minimum set-up margin of 5-6 mm is recommended when patient set-up is based on bony landmarks and of 2-3 mm when the head-repositioning device is used.

The purpose of this pilot study was to evaluate lymph node enhancement with an indirect magnetic resonance (MR) lymphography technique using 2 different contrast agents in the head and neck region of healthy dogs. Five dogs were imaged at various times after intradermal injection of gadoversetamide and Gadofluorine M (minimum of 1 week apart) in the right and left mandibular, temporal, and lateral neck regions. We observed consistent progressive enhancement with time in the mandibular, retropharyngeal, and superficial cervical lymph nodes. The node enhancement was comparable for both contrast agents. Contrast enhancement of the parotid lymph nodes was not seen. We conclude that this technique of indirect MR lymphography using either agent could be used to identify those lymph nodes at highest risk of metastatic disease in dogs with cancer, and to guide staging and treatment.

Radiation treatment planning is performed on images that do not take variation in patient position into account. To compensate for expected variations in position of the patient, a three-dimensional expansion of the clinical target volume, or set-up margin, is added. Variations in patient position can be decreased through use of an immobilization device, allowing selection of a smaller set-up margin. The objective of this prospective study was comparison of interfractional variation in patient position between set-ups of the canine head region using palpation of bony landmarks and set-ups using a head-repositioning device. Fiducial markers were attached to the skull bones of three research dogs, and the dogs were positioned as for a typical radiation treatment of the head region using both set-up methods. A kilovoltage on-board imager was used to acquire orthogonal images and the difference between the x-, y-, and z-axis coordinates of each fiducial marker relative to the initial reference isocenter was measured. The difference in patient position for each axis coordinate was significantly lower for set-ups using the head-repositioning device than for set-ups using bony landmarks (P0.05). Ninety-five percent of the absolute values of the displacement vector differences were4.62 mm for set-up using bony landmarks, and1.93 mm for set-up using the head-repositioning device. A minimum set-up margin of 5-6 mm is recommended when patient set-up is based on bony landmarks and of 2-3 mm when the head-repositioning device is used.