Aatman Chand, Ashis K Chand and Arun Angelo Patil
CT guided biopsy of extracranial lesion is a common procedure. Free hand technique is usually used for this procedure. Other methods include ultrasound guidance and the use of navigation system. In this paper the authors describe the use of stereotactic frame to perform these procedures. The system has a base plate which attaches the system to the CT table. It has side plates and pneumatic bags to secure the patient in place. The frame is L shaped; and is fitted to the base plate. It can be adjusted in the Y axis (dorsalventral height). The horizontal arm has a cylindrical clamp that can slide along the X-axis (side to side). The clamp holds a cylindrical probe carrier which can slide along the Z-axis (cranial caudal) and can rotate in the coronal plane. One end of the probe carrier has a probe holder attached to it which be adjusted in the sagittal plane to any required angle. CT scans are obtained, and the target is identified. The table is moved to bring the target plane of the scan in the plane of the vertical laser positioning light on the CT gantry. The cylindrical probe carrier is the moved along the Z axis to bring the middle of the probe holder in the plane of the laser positioning light. Another set of scans are obtained. The probe holder is identified in the plane of the target. Measurements and calculations are then done to give the length of the probe needed and the angle of the trajectory in both coronal and sagittal planes. The target is then probed; and the accuracy is checked by intraoperative scans. Thirty procedures were performed using this system. Accuracy of probe placement was within ~2.95 mm along X and Y axis and ~1.5 mm along the Z axis, though the probe was always in the lesion. This accuracy can be further improved using mathematical calculation described in the paper. This is a simple device which can set optimal trajectory of the probe holder to reach the target with good accuracy using intraoperative CT images. The system also provides stability to the probe during biopsy procedures.