Characterization and commissioning of a Leksell Gamma Knife ICON system for framed and frameless stereotactic radiosurgery

Abstract

Purpose The Leksell Gamma Knife Icon unit (IU) was introduced recently as an upgrade to the Perfexion unit (PU) at our Gamma Knife practice. In the current study, we sought mainly to characterize dosimetry and targeting accuracy of the IU treatment deliveries using both invasive frame and frameless treatment workflows. Methods Relative output factors were measured by delivering single‐shot 4, 8 and 16 mm radiation profiles in the manufacturer's acrylonitrile butadiene styrene spherical phantom in coronal and sagittal planes using EBT3 film. Resultant dosimetry was compared with the manufacturer's dose calculation and derived output factors were compared with the manufacturer's published value. Geometric consistency of stereotactic coordinates based on cone‐beam computed tomography (CBCT) versus the traditional conventional CT‐based method was characterized using a rigid phantom containing nine fiducial indicators over four separate trials. End‐to‐end (E2E) testing using EBT3 film was designed to evaluate both dosimetric and geometric accuracy for hypothetical framed and frameless workflows. Results Relative output factors as measured by the manufacturer were independently confirmed using EBT3 film measurements to within 2%. The mean 3D radial discrepancy in stereotactic space between CBCT and CT‐based definition over the sampled locations in our rigid geometry phantom was demonstrated to be between 0.40 mm and 0.56 mm over the set of trials, larger than prior reported values. E2E performed in 2D demonstrates sub‐mm (and typically < 0.5 mm) accuracy for framed and frameless workflows; geometric accuracy of framed treatments using CBCT‐defined stereotactic coordinates was shown to be slightly improved in comparison with those defined using conventional CT. Furthermore, in phantom, frameless workflows exhibited better accuracy than framed workflows for fractionated treatments, despite large magnitudes of introduced interfraction setup error. Accuracy of dosimetric delivery was confirmed in terms of qualitative comparisons of dose profiles and in terms of 2D gamma pass rates based on 1%/1 mm criteria. Conclusion The IU was commissioned for clinical use of frameless and framed treatment protocols. The present study outlines an extensive E2E methodology for confirmation of dosimetric and geometric treatment accuracy.

Machine performance and stability of the first clinical self‐shielded stereotactic radiosurgery system: Initial 2‐year experience

“…Targeting errors of 0.4-0.5 mm have been reported for E2E tests on the CK system using the 6D skull tracking algorithm 26,32,38 while mean 2D E2E targeting errors of 0.429 mm (maximum: 0.718 mm) and 0.225 mm (maximum: 0.284 mm) have been reported for framed and frameless GK. 39 Film-based DQA measurements for all ZAP-X treatments were within the TG-135 recommendation of a gamma pass rate of 90% for 2%/2 mm criteria. Average gamma pass rate results (averaging over all 80 DQA measurements) were 99.0% and 90.5% for 2%/2 mm and 2%/1 mm gamma criteria, respectively.…”

“…Average total targeting errors observed for the ZAP‐X are similar to those reported for E2E tests performed on other SRS systems. Targeting errors of 0.4–0.5 mm have been reported for E2E tests on the CK system using the 6D skull tracking algorithm 26,32,38 while mean 2D E2E targeting errors of 0.429 mm (maximum: 0.718 mm) and 0.225 mm (maximum: 0.284 mm) have been reported for framed and frameless GK 39 …”

New technologies and machines for stereotactic radiation therapy

“…Each sector can move over a drilled tungsten collimation ring system, which has three collimating diameters of 4, 8, and 16 mm 9 . The LGK Icon model differs from its predecessors mainly in its capabilities of non‐invasive frameless procedures 10 . Two image‐guidance systems are introduced to the machine: a cone beam CT imaging system with an X‐ray tube and image detector, and an intra‐fraction motion management system based on infrared lights.…”

Avoiding a Collision in Gamma Knife Radiosurgery : A Modified Mask Fixation Method

“…CBCT imaging and high-definition motion management (HDMM) systems based on infrared (IR) light have been introduced to provide submillimeter accuracy for stereotactic radiosurgery (SRS) treatment 2,3,5) . With the advent of LGK Icon, physicians are able to offer noninvasive mask fixation for SRS treatment to patients either unwilling or unable to undergo invasive frame fixation 7,8) . Infrequently, a treatment plan could be canceled if a planned beam cannot be delivered because of a collision between the collimator helmet and the patient's skull or frame including the screw 12) .…”