Performance of the cone beam computed tomography‐based patient positioning system on the Gamma Knife Icon™

Abstract

Purpose Cone beam computed tomography (CBCT) imaging has been implemented on the Leksell Gamma Knife® Icon™ for assessing patient positioning in mask‐based Gamma Knife radiosurgery. The purpose of this study was to evaluate the performance of the CBCT‐based patient positioning system as a tool for frameless Gamma Knife radiosurgery. Methods Daily quality assurance (QA) CBCT precision test results from a 12‐month period were analyzed for the geometric accuracy and the stability of the imager. The performance of the image acquisition module and the image registration algorithm was evaluated using an anthropomorphic head phantom (CIRS Inc., Norfolk, VA) and a XYZR axis manual positioning stage (TOAUTO Inc., Guangdong, China). The head phantom was fixed on a mask adaptor and manually translated in the X, Y, Z directions or rotated around the X, Y, Z axes in the range of ±10 mm or ±10º. A CBCT scan was performed after each manual position setup followed by an image registration to the reference scan. To assess the overall setup uncertainties in fractionated treatment, two cylindrical Presage phantoms (Heuris Inc., Skillman, NJ) of 15 cm diameter and 10 cm height were irradiated with identical prescription dose and shot placement following standard mask‐based treatment workflow according to two different fraction schedules: a single fraction treatment of 7.5 Gy and a 5‐fraction treatment with 1.5 Gy per fraction. Results The averaged vector deviations of the four marks from their preset values are 0.087, 0.085, 0.095, and 0.079 mm from the 212 daily QA tests. The averaged displacements in the X, Y, Z coordinates and the pitch, yaw, roll angles from the image registration tests are 0.23, 0.27, 0.14, 0.32º, 0.19º, 0.31º from the manual setup. The corresponding maximum differences are 0.41, 0.33, 0.29 mm, 0.45º, 0.31º, and 0.43º, respectively. Compared to the treatment plan using the 2% & 1 mm criteria, the averaged 2D Gamma passing rate is 98.25% for the measured dose distribution from the Presage phantom with 1‐fraction irradiation and 95.12% for the 5‐fraction irradiation. The averaged Gamma passing rates are 99.53% and 98.16% for the 1‐fraction and 5‐fraction irradiations using the 2% & 2 mm criteria. Conclusions The CBCT imager and the image registration algorithm can reproduce phantom position with <0.5 mm/0.5º uncertainty. A systematic contribution from the interfraction phantom repositioning procedure was observed in the Gamma analysis over the irradiated volumes of two end‐to‐end test phantoms.

Mask-Based versus Frame-Based Gamma Knife ICON Radiosurgery in Brain Metastases: A Prospective Randomized Trial

“…The upheaval of the introduction of the ICON led us to perform all the hypo-fractionated procedures (mainly para-optic meningiomas encasing the visual pathways) mask-based. Assessment of this technology has demonstrated, in our team and in others, its excellent reliability, precision, and accuracy [12, 20, 21]. On the first day, the MRI and CT of the day serving for the preplanning are co-registered with the first CBCT with a demonstrated high accuracy [11].…”

Retrospective Analysis of Treatment Workflow in Frame-Based and Frameless Gamma Knife Radiosurgery

“…Previous generations of GK units exclusively employed a frame-based system for patient immobilization and stereotactic localization [2]. Gamma Knife Icon™ (GKI), the newest generation of GK unit introduced in 2015, is equipped with a cone-beam computed tomography (CBCT) system, which allows stereotactic localization of patients immobilized using a frameless approach, i.e., a thermoplastic mask [3,4]. Frameless immobilization avoids the trauma from the placement of a traditional stereotactic frame and is ideal for the delivery of multifraction SRS [5,6].…”