The associated targets methodology and the multi-isocenters radiosurgery treatment planning system Artemis-3D.

A new radiosurgical methodology, the "associated targets methodology" has been developed and tested by our group for the irradiation of complex cerebral arteriovenous malformations using our treatment planning system Artemis-3D. For the treatment of the arteriovenous malformations we used 15 MV photons generated by a Saturne 43 Linac, eight additional collimators (6-20 mm in diameter), the Betti fixation seat and the Talairach stereotactic frame. The successive steps of the associated targets' methodology are: -the prescription of a peripheral minimal therapeutic effective dose corresponding to the 60-70% cumulated isodose range; -the compartmentalization of the target volume into several sub-volumes, each of them having its own isocenter, collimator, irradiation space and isocenter dose weight; -the 3-dimensional computation and graphics requirements, and dose volume analysis; -the optimization evaluation criteria taking into account the dose inside and outside of the lesion. Two treatment planning software versions of Artemis-3D exist; the first one was developed for the sitting position and later for the supine treatment position, the second version is a multi-modalities imagery radiosurgical treatment planning system based on more powerful computers. Different types of stereotactic frames have been integrated. Three-dimensional visualization, stereotactic CT imaging, and angiography can be used for the sitting or supine position. We started using this methodology in 1990, and treated 44 patients during that year. For 26 single isocenter arteriovenous malformations, the obliteration rate was 22/26 (85%). In the 18 multi-isocenters irradiation cases, the overall obliteration rate was 11/18 = 61%. An example of successfully irradiated complex arteriovenous malformation is discussed to illustrate the methodology. With this three-dimensional methodology we have improved the results obtained during the first period (1986 to 1989) of our radiosurgical practice in which we used a two dimensional planification approach.