AbstractID: 8550 Title: Early Experiences with Fiducial Tracking for Spinal Treatments with the
CyberKnife
The CyberKnife is a robot-mounted 6MV linear accelerator approved for radiation therapy anywhere in the body. For spinal
treatments, fiducials are placed near the lesion during surgery or percutaneously. Treatment set-up requires only a standard vacuum
bag or other simple immobilization devices. CT treatment planning locates the contoured tumor volume(s) and critical structures with
reference to fiducials and dose distributions. During treatment, two orthogonal radiograph devices image the anatomy and Dynamic
Tracking Software compares these views with DRRs from the CT images. This allows 6-D fiducial tracking for lesion targeting
during treatment. Initial positioning is being done interactively until the translational and rotational differences between real-time and
DRR images of the fiducial array are less than 1 mm and 1 degree, respectively. This is visually verified using anatomical landmarks.
Migration of some fiducials has been observed. These have generally been in soft tissues but occasionally have occurred in
deteriorated bone as well. These have been identified with respect to the fiducial constellation and turned off for localization. Our
goal is • ILGXFLDOV ZLWK ! FP VHSDUDWLRQ EHWZHHQ HDFK SDLU DOORZLQJ -D tracking. This requires initial placement of 5 or 6 fiducials
in the bony regions near the lesion with attention given to adequate separation. One to five fractions have been used with delivered
doses of 12 to 24 Gy. To date, clinical response has been favorable with pain relief occurring surprisingly soon, often after the first or
second fraction. Accumulated data, fiducial array radiographs and discovered concerns are presented.