Gamma Knife ® icon CBCT offers improved localization workflow for frame‐based treatment

Purpose To assess differences between frame‐based and cone beam computed tomography (CBCT)‐defined stereotactic space and to identify predictors of the observed findings. Methods and materials Differences between frame‐based and CBCT‐defined stereotactic space after image co‐registration were reviewed for 529 patients. Treatment planning system reported the information about the shifts in X, Y, and Z coordinates of the center of the stereotactic space (i.e., coordinate X = 100 mm, Y = 100 mm, and Z = 100 mm) defined by the frame, and the maximum shot displacement (MSD) in mm. We collected the potential predictors of the differences. In total, 19 factors were investigated. We used multiple linear regression to evaluate associations with the increased differences. Results Rotational and translational shifts greater than 1° and 1 mm, respectively, were observed in 2.6% of patients. At the same time, a decrease in tumor coverage of more than 5% was detected in 8.3% of cases. It was revealed that the higher fiducial errors (both mean and maximum), the greater weight of the patient, and the lower Karnofsky Performance Scale were predictors of increased rotational, translational shifts, and the MSD.

“…suggested that CBCT improves traditional methods by defining stereotactic coordinates at the time of patient docking into the Gamma Knife couch and seems to be more reliable. [ 14 ]…”

Section: Discussionmentioning

confidence: 99%

Discrepancies between frame‐ and CBCT‐based stereotactic space definition on the Gamma Knife Icon

Bannikova

Dalechina²,

Kostjuchenko³

et al. 2022

“…Expecting the known uncertainty discussed in this article, we might add a margin, such as 1 mm, for the treatment of a G‐framed patient to reduce the problematic warnings. Alternatively, we can stop the use of the MR/CT indicator box for coordinate definition by using CBCT even with G‐framed patients as proposed by Duggar et al 15 Yet, another solution is to enable the LGP to adjust the head position using the geometrical translation and rotation data obtained by co‐registration of CBCT and plan reference image sets with the G‐framed patient as done with all masked patients.…”

Section: Discussionmentioning

confidence: 99%

Utilization of CBCT to improve the delivery accuracy of Gamma Knife radiosurgery with G‐frame

Claps

Mathew

Dusenbery

et al. 2021

To quantify the G-frame based stereotactic coordinate definition accuracy of Leksell coordinate G-frame-based Gamma Knife radiosurgery (GKRS) by the on-board cone-beam CT (CBCT) and establish remedial action rules to minimize the delivery errors. Methods:We analyzed the data of 108 patients (a total of 201 tumors) treated by GKRS with G-frame for head fixation. After co-registering the CBCT images and plan reference images, the Leksell GammaPlan (LGP) treatment planning system provided the amount of geometric translation and rotation required to minimize the position difference between the plan and treatment. The software also calculated maximum displacement, which characterizes the position shift more clearly. We studied how much these predicted dosimetric quantities changed if the treatment was delivered without correcting the patient's position. Results:The maximum displacement of the patient position obtained from the co-registration of CBCT and plan reference images was 0.81 ± 0.38 mm (0.24-2.03 mm). The target coverage decreased by 3.3 ± 7.0% on average (−48.5% to +35.7%). The decrease of the target coverage, however, became smaller as the target volume increased. In particular, if the volume was greater than 2 cm 3 , the %change in target coverage was always less than −5%. Conclusions:The position differences reported by the registration module of LGP were within the accuracy limit of image registration for most clinical cases, but the errors could be larger in some cases. Therefore, we propose the following decision process. We do not advise position adjustment for G-frame based GKRS if the maximum displacement is less than 1 mm. When this limit is exceeded, however, another criterion should be applied to the decision making by considering the tumor size (or the treatment volume) together with the acceptable change of the tumor coverage.

“…Numerous prior studies on the IU have been conducted, including general descriptions of commissioning experiences, 1 assessment of the accuracy 2 , 3 and quality assurance 4 (QA) of the image guidance system. Past studies on the previous PU model have assessed the stability of the definition of stereotactic coordinates using a stereotactic head frame, 5 commissioning and QA of the automatic positioning system, 6 QA of the PU beam accuracy, 7 , 8 and evaluation of the dose calculation software 9 and a secondary dose calculation system.…”

Section: Introductionmentioning

confidence: 99%

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

Hickling

Qian

et al. 2022

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.