Multistage stereotactic radiosurgery for large cerebral arteriovenous malformations using the Gamma Knife platform

Abstract

Purpose: Radiosurgery is an established technique to treat cerebral arteriovenous malformations (AVMs). Obliteration of larger AVMs (> 10-15 cm³ or diameter > 3 cm) in a single session is challenging with current radiosurgery platforms due to toxicity. We present a novel technique of multistage stereotactic radiosurgery (SRS) for large intracranial arteriovenous malformations (AVM) using the Gamma Knife system.

Materials/methods: Eighteen patients with large (> 10-15 cm³ or diameter > 3 cm) AVMs, which were previously treated using a staged SRS technique on the Cyberknife platform, were retrospectively selected for this study. The AVMs were contoured and divided into 3-8 subtargets to be treated sequentially in a staged approach at half to 4 week intervals. The prescription dose ranged from 15 Gy to 20 Gy, depending on the subtarget number, volume, and location. Gamma Knife plans using multiple collimator settings were generated and optimized. The coordinates of each shot from the initial plan covering the total AVM target were extracted based on their relative positions within the frame system. The shots were regrouped based on their location with respect to the subtarget contours to generate subplans for each stage. The delivery time of each shot for a subtarget was decay corrected with ⁶⁰ Co for staging the treatment course to generate the same dose distribution as that planned for the total AVM target. Conformality indices and dose-volume analysis were performed to evaluate treatment plans.

Results: With the shot redistribution technique, the composite dose for the multistaged treatment of multiple subtargets is equivalent to the initial plan for total AVM target. Gamma Knife plans resulted in an average PTV coverage of 96.3 ± 0.9% and a PITV of 1.23 ± 0.1. The resulting Conformality indices, V_12Gy and R₅₀ dose spillage values were 0.76 ± 0.05, 3.4 ± 1.8, and 3.1 ± 0.5 respectively.

Conclusion: The Gamma Knife system can deliver a multistaged conformal dose to treat large AVMs when correcting for translational setup errors of each shot at each staged treatment.

Keywords: Gamma Knife; arteriovenous malformation; stereotactic radiosurgery.

Figure 1

Multistage SRS of large AVM using Gamma Knife. (a) Shots are divided among two stages depending on the center location of each shot. (b) Example dose distribution for each staged treatment of individual sub‐targets.

Figure 2

Simulation of Gamma Knife treatment by combining an image of the Gamma Knife frame and an MRI image for a Cyberknife treatment. (a) Gamma Knife frame MRI image. (b) Patient MRI image. (c) Combined Gamma Knife frame and patient MRI images.

Figure 3

Shots repositioned to compensate for translational setup errors. (a) Original plan for entire AVM target. (b) Setup error after repositioning the patient in the next staged treatment. Shots are repositioned to compensate for translational setup errors depending on the image registration.

Figure 4

Phantom study of the ICON system. (a) Irradiation with the ICON frameless system. (b) Anthropomorphic phantom with film. (c) Irradiation for entire AVM target to be used as the reference dose distribution. (d) First stage irradiation (e) Cumulative dose distribution from the first and second stages with random setup errors. (f) Cumulative dose distribution from all stages with random setup errors.

Figure 5

Residual rotational errors after compensation of translational setup errors depending on a rotation angle of ±1°, ±3°, and ±5° in (a), (b), and (c) respectively. [Color figure can be viewed at wileyonlinelibrary.com]