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 performed to investigate the feasibility of delineating an AVM on MR images and to compare the AVM volume outlined on different images. Conventional stereotaxic angiograms, stereotaxic MR images and MR angiograms using several different pulse sequences were obtained prior to radiosurgery. Treatment plans were made from the conventional stereotaxic angiograms. These plans were then transferred to a separate dose planning computer which displayed the MR images with the superimposed isodose lines. The radiated volumes of AVM and brain tissue were measured from these MR images. Last, an assessment was made of the radiation volume needed for an appropriate treatment of the AVM if the treatment plan was made from the MR images rather than from the conventional stereotaxic 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 AVM nidi were found to be larger on the conventional stereotaxic angiograms than on the stereotaxic MR images. Consequently, a dose plan based on a conventional stereotaxic angiogram would result in a higher integral dose to the brain with the same target dose. By using reliable MR information it is expected that the volume of brain exposed to radiation could be decreased and the adverse effects of stereotactic radiosurgery for AVM thereby minimized.