Extracranial radiosurgery: Immobilizing liver motion in dogs using high-frequency jet ventilation and total intravenous anesthesia

Purpose: Extracranial radiosurgery requires control of organ motion. The pu rpose of this study is to quantitatively determine the extent of liver moti on in anesthetized dogs with continuous i.v. propofol infusion with or with out muscle relaxants and high frequency jet ventilation. Methods and Materials: Five dogs were used in the experiment. Each dog was restrained while anesthetized in the supine position using an alpha cradle. Surgical metal clips were implanted around the liver periphery so that its motion could be visualized using a fluoroscopic imaging device in a conven tional simulator. Initially, two orthogonal simulation films were taken to correlate locations of implanted clips. Two orthogonal views of fluoroscopi c images for each anesthetized dog were recorded on a magnetic tape and ana lyzed from the post-imaging data. Liver motion was documented under the fol lowing three conditions: 1) ventilated with a conventional mechanical venti lator, 2) ventilated with a high-frequency jet ventilator, and 3) ventilate d with a high-frequency jet ventilator and total muscle paralysis (with vec uronium injection). The maximum liver motion for each dog was analyzed in t hree orthogonal directions: the inferior-to-superior direction, the anterio r-to-posterior direction, and the right-to-left direction. Results: When the anesthetized dogs were ventilated with a conventional mec hanical ventilator, the average liver motions were 1.2 cm in the inferior-t o-superior direction, 0.4 cm in the anterior-to-posterior direction, and 0. 2 cm in the right-to-left direction, respectively. After the introduction o f high-frequency jet ventilation, the average liver motions were reduced to 0.2 cm in the inferior-to-superior direction, 0.2 cm in the anterior-to-po sterior direction, and 0.1 cm in the right-to-left direction. The maximum l iver motion was dependent on ventilator settings. There was no additional m easurable motion reduction with the addition of the muscle relaxant. Conclusion: The liver motion in each anesthetized dog was controlled under 3.0 mm in all directions with the use of high-frequency jet ventilation. No detectable advantage was identified by the injection of muscle relaxant in terms of further reducing the liver motion. The preclinical animal study i ndicated that the use of high-frequency jet ventilation (HFJV) would be abl e to limit the liver motion to an extent acceptable for the application of extracranial radiosurgery in humans. Radiosurgery for localized liver tumor s warrants further investigation. (C) 2001 Elsevier Science Inc.