TARGET DELINEATION IN RADIOSURGERY FOR CEREBRAL ARTERIOVENOUS-MALFORMATIONS - ASSESSMENT OF THE VALUE OF STEREOTAXIC MR-IMAGING AND MR-ANGIOGRAPHY

A study of 6 selected arteriovenous malformation (AVM) patients was pe rformed to investigate the feasibility of delineating an AVM on MR ima ges and to compare the AVM volume outlined on different images. Conven tional stereotaxic angiograms, stereotaxic MR images and MR angiograms using several different pulse sequences were obtained prior to radios urgery. Treatment plans were made from the conventional stereotaxic an giograms. These plans were then transferred to a separate dose plannin g computer which displayed the MR images with the superimposed isodose lines. The radiated volumes of AVM and brain tissue were measured fro m these MR images. Last, an assessment was made of the radiation volum e needed for an appropriate treatment of the AVM if the treatment plan was made from the MR images rather than from the conventional stereot axic angiogram. It was possible to delineate medium and large size AVM nidi on stereotaxic MR images based on an integration of information obtained from various pulse sequences. The estimated volumes of the AV M nidi were found to be larger on the conventional stereotaxic angiogr ams than on the stereotaxic MR images. Consequently, a dose plan based on a conventional stereotaxic angiogram would result in a higher inte gral dose to the brain with the same target dose. By using reliable MR information it is expected that the volume of brain exposed to radiat ion could be decreased and the adverse effects of stereotactic radiosu rgery for AVM thereby minimized.