C Mendez*, E Gete, BC Cancer-Vancouver, Vancouver, BCCA, CA

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  C Mendez

PO-GePV-T-429 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To investigate the feasibility of Volume Staged SRS (VS-SRS) for AVMs on a linear accelerator using Volumetric Modulated Arc Therapy (VMAT) and a frameless patient positioning system.

Methods: Ten patients previously treated with fractionated SRS were selected for this study. The AVM sizes ranged from 1.6 to 4.4 cm in diameter. For each patient, two sets of VS-SRS plans were created on the Varian Eclipse TPS using the TrueBeam STx linac. One set, called PTV-VMAT used the (PTV=AVM+1mm) as a target. The second set, called AVM-VMAT was planned with the AVM as the target. The treatment planning technique was developed based on sample VS Gamma Knife (GK) plans. The effect of a 1-mm PTV margin on normal brain dose was investigated. GaFchromic EBT3 film measurements were performed for each staged plan to investigate the positioning uncertainty near the field junction. Point dose measurements were performed using a PTW microDiamond detector.

Results: The AVM-VMAT plans for one of the patients resulted in lower AVM maximum dose, and comparable target coverage and dose falloff when compared to the sample GK plans. Six of the ten PTV-VMAT plans met the normal tissue constraints and target coverage. When compared to the AVM-VMAT plans, the addition of a 1 mm margin results in a 48.9% average increase of the normal brain V(12Gy). Agreement of point dose measurements to treatment planning calculations averaged -0.6%. Gamma analysis of all film measurements was above 90% for the 2%, 1 mm criteria for the film-to-film comparison, and 5%, 1 mm, for film-to-TPS.

Conclusion: This work suggests that VMAT is capable of producing VS-SRS plans that have similar dose falloff characteristics as GK plans. Normal brain dose is highly dependent on PTV margin size, and two-stage treatment setups do not appear to contribute additional uncertainty to treatment delivery.

Keywords

Artero-venous Malformations, Linear Accelerator, Stereotactic Radiosurgery

Taxonomy

TH- External Beam- Photons: intracranial stereotactic/SBRT

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