The Elekta Fraxion™ system is not suitable for maxillary fixation in canine conformal radiation therapy techniques.

Abstract

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&#x2122; 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&#xb0; (yaw), 10.9&#xb0; (pitch), and 4.5&#xb0; (roll). The mean systematic translational errors were 4.7, 2.6, and 2.3&#xa0;mm, mean random translational errors were 3.0, 2.2, and 2.5&#xa0;mm, and mean overall translational errors were 2.4, 0.7, and 2.3&#xa0;mm in the cranial-caudal, lateral, and dorsal-ventral directions, respectively. The mean systematic rotational errors were 1.17&#xb0;, 0.77&#xb0;, and 1.43&#xb0;, the mean rotational random errors were 1.65&#xb0;, 1.46&#xb0;, and 1.34&#xb0; and the mean overall rotational errors were 0.56&#xb0;, 0.22&#xb0;, and 0.29&#xb0; in the yaw, pitch, and roll directions, respectively. The mean error of the three-dimensional vector was 6.9&#xa0;mm with a standard deviation of 3.8&#xa0;mm. Ninety-five percent of the three-dimensional vectors were&#xa0;<14.8&#xa0;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.