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Abstract
The aim of this study was to assess the accuracy and stability of frameless gamma knife radiosurgery (GKRS). The accuracies of the radiation isocenter and patient couch movement were evaluated by film dosimetry with a half‐year cycle. Radiation isocenter assessment with a diode detector and cone‐beam computed tomography (CBCT) image accuracy tests were performed daily with a vendor‐provided tool for one and a half years after installation. CBCT image quality was examined twice a month with a phantom. The accuracy of image coregistration using CBCT images was studied using magnetic resonance (MR) and computed tomography (CT) images of another phantom. The overall positional accuracy was measured in whole procedure tests using film dosimetry with an anthropomorphic phantom. The positional errors of the radiation isocenter at the center and at an extreme position were both less than 0.1 mm. The three‐dimensional deviation of the CBCT coordinate system was stable for one and a half years (mean 0.04 ± 0.02 mm). Image coregistration revealed a difference of 0.2 ± 0.1 mm between CT and CBCT images and a deviation of 0.4 ± 0.2 mm between MR and CBCT images. The whole procedure test of the positional accuracy of the mask‐based irradiation revealed an accuracy of 0.5 ± 0.6 mm. The radiation isocenter accuracy, patient couch movement accuracy, and Gamma Knife Icon CBCT accuracy were all approximately 0.1 mm and were stable for one and a half years. The coordinate system assigned to MR images through coregistration was more accurate than the system defined by fiducial markers. Possible patient motion during irradiation should be considered when evaluating the overall accuracy of frameless GKRS.
Highlights
| INTRODUCTIONFrameless gamma knife radiosurgery (GKRS) can be performed with the latest gamma knife model, Gamma Knife (GK) IconTM [Fig. 1(a)]
The contrast to noise ratio (CNR) of the cone-beam computed tomography (CBCT) images was calculated using the mean and standard deviation of pixel values measured in a polystyrene insert and in a low-density polyethylene (LDPE) insert located inside the phantom
An anthropomorphic phantom is fixed to the Gamma Knife (GK) Icon with a mask system for a whole procedure test of the accuracy of frameless gamma knife radiosurgery (GKRS)
Summary
Frameless gamma knife radiosurgery (GKRS) can be performed with the latest gamma knife model, Gamma Knife (GK) IconTM [Fig. 1(a)]. After a treatment plan is completed based on this coordinate system, the patient is fixed by a mask, and another set of CBCT images is obtained such that the deviations in patient position can be automatically corrected. If the motion is maintained at levels greater than the limit for 30 seconds, the patient couch moves out, and CBCT imaging is repeated to correct for the movement. The overall accuracy of the frameless GKRS depends on numerous factors that can be classified into three groups: radiation-related factors, imagerelated factors, and patient motion. The accuracy and stability of the radiation isocenter, the accuracy of patient couch movement, the accuracy and stability of CBCT images, the accuracy of image coregistration, and the accuracy of the HDMM system were assessed. The results were compared with the accuracy and image quality obtained at the time of machine commissioning[13] and with the short-term stability of the CBCT system.[14]
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