SU‐E‐T‐577: Stereotactic Radiosurgery for AVMs: Impact of Embolization Media on Radiation Dose

• Published in: Medical Physics Vol. 38; no. 6; p. 3622
• Main Authors: Beachey, D, Da Costa, L, ter Brugge, K, Andrade‐Souza, Y, Howard, P, Tsao, M, Schwartz, M, Sahgal, A
• Format: Conference Proceeding Journal Article
• Language: English
• Published: American Association of Physicists in Medicine 01-06-2011
• Subjects: Onyx; Radiosurgery; Tissue engineering
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3612539

Purpose: We investigate the dosimetric impact of surgical embolization of Arteriovascular‐malformations (AVM's) on further follow‐up Stereotactic Radiosurgery. Two embolization media are studied. By introducing a tissue inhomogeneity, the breakdown in electron equilibrium at the interface impacts actual tissue dose within a few mm. As this is the precise location of the target tissue the dose departure from standard prescription is to be quantified. Methods: Inhomogeneity phantoms were constructed to model regions of various thickness 2mm – 16mm. Each phantom was constructed of a tissue equivalent material while drilled embolization cavities were filled with 4 different admixtures of embolizing media: Onyx (TM) with contrast‐ to‐polymer ratio 18% and 34%; and Embucrilate (TM) (33% and 50%). Near tissue‐equivalent radiochromic film was placed in planes 0, 1, and 2mm up‐beam and down‐beam from the inhomogeneity. The simulated embolizations and films were then irradiated in a 6MV radiosurgery beam at tissue depth of 7cm. Results: In a narrow beam geometry, we observe an immediate depletion of dose at the interface downstream of the Onyx medium of up to 20% compared to 18% for the Embucrilate. The dose enhancement immediately upstream of the embolization medium interface is typically 25% for the Onxy and 15% for Embucrilate. Conclusions: While radiosurgery beams are typically directed from a large range of angles, the two connected dose interface effects tend to cancel only laterally. Typical beam arrangements have a superior‐to‐inferior directional bias and the inhomogeneity interface effects on dose will have an effect on the target tissue at those aspects of the embolized portions of the AVM lesion.