The role of CT myelography in sparing the spinal cord during definitive radiotherapy in vertebral hemangioma.

INTRODUCTION

The spinal cord is poorly visualized on CT images but is well visualized in MRI images. However, implants used for spinal stabilization can produce artifacts on the MRI images which can interfere with identification of the cord. CT myelography in conjunction with CT simulation helps to clearly delineate the cord.

MATERIALS AND METHODS

CT simulation was done in a patient with vertebral hemangioma. Pre- and post myelography images were obtained. Two plans were generated on pre and post myelography CT images using Eclipse™ treatment planning system (TPS) version 10.0, Varian Medical Systems, USA. The prescribed total dose to PTV was 40 Gy in 20 fractions.

RESULTS

The cord was poorly visualized in the premyelogram CT images. The titanium implants used for spinal cord stabilization produced artifacts in the MRI images. Figure  Post myelogram, the contrast lit up the spinal cord. There was an overlap of 0.75 cc volume of the spinal cord with the PTV in the premyelogram images. This volume was reduced to 0 cc in the post myelogram images. There was an overlap of 5.4 cc volume of the PRV of spinal cord with the PTV in the premyelogram images which was reduced to 1 cc in the post myelogram images. The overlap region between the PTV and spinal cord received around 71% of the prescribed dose in premyelogram CT could be reduced to 0% in the post myelogram CT. The mean dose received by the overlap PRV spinal cord and PTV could be increased from 70% in the premyelogram to 92% in the post myelogram plans.

CONCLUSION

CT myelogram in conjunction with CT simulation is particularly useful in cases where the tumor margin is very close to the cord and spinal implants are causing distortion of magnetic resonance images.