title: Radiosurgical treatment planning of AVM following embolization with Onyx: possible dosage error in treatment planning can be averted.
abstract: Treatment of arteriovenous malformations (AVM) of the brain is challenging due to the size and location of the nidus-proper and its proximity to the cerebrovascular circulation. Recent advances in catheter techniques and new embolization materials such as Onyx (a liquid agent that is less adhesive and slowly polymerizing) have increased the probability of achieving obliteration. When planning radiosurgical cases following such embolization, however, one must be cognizant of the distortions introduced by this novel substance on imaging studies. A sample of Onyx was irradiated to define the attenuation per mm thickness. The difference in attenuation compared to water was determined. Dose calculations were performed using 3 methods of inhomogeneity corrections. Homogeneous calculations were compared to "standard" heterogeneity corrections and to "modified" heterogeneity corrections by assigning individual electron densities to the normal brain and the Onyx. The difference between the attenuation of water in comparison to the Onyx was approximately 3% for beam energy of 6 MV. Best calculation results were achieved when using the modified inhomogeneity corrections which were based on the actual attenuation of the Onyx. The use of Onyx caused significant image artifact on MR and especially CT. As such, a correction must be manually introduced into the planning system to account for this potential error. Otherwise, dose calculation may be unreliable and could have dire consequences for patients receiving high doses of radiotherapy.
authors.affiliation: TASMC Stereotactic Radiosurgery Unit and the Institute of Radiotherapy, Tel Aviv Sourasky Medical Center University of Tel Aviv, 6 Weizman Street, 64239, Tel Aviv, Israel. natans@tasmc.health.gov.il
authors.forename: Natan
authors.initials: N
authors.lastname: Shtraus
authors.forename: Dan
authors.initials: D
authors.lastname: Schifter
authors.forename: Benjamin W
authors.initials: BW
authors.lastname: Corn
authors.forename: Shimon
authors.initials: S
authors.lastname: Maimon
authors.forename: Shlomi
authors.initials: S
authors.lastname: Alani
authors.forename: Vladimir
authors.initials: V
authors.lastname: Frolov
authors.forename: Diana
authors.initials: D
authors.lastname: Matceyevsky
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Kanner
mesh_terms: D001165:Arteriovenous Malformations / Q000628:therapy*; D003952:Diagnostic Imaging; D004121:Dimethyl Sulfoxide; D004621:Embolization, Therapeutic / Q000379:methods*; D005500:Follow-Up Studies; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D011145:Polyvinyls; D011300:Preoperative Care; D016634:Radiosurgery / Q000379:methods*; D011878:Radiotherapy; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome
chemical_list: C450660:Onyx copolymer; D011145:Polyvinyls; D004121:Dimethyl Sulfoxide
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