Target and peripheral dose during patient repositioning with the Gamma Knife automatic positioning system (APS) device (original) (raw)
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International Journal of Radiation Oncology*Biology*Physics, 2007
To measure radiation exposure to a patient during head repositioning with the automatic positioning system (APS) for Gamma Knife radiosurgery. A 16-cm diameter spherical solid phantom, provided by the manufacturer, was mounted to the APS unit using a custom-made holder. A small-volume ionization chamber (0.07-cm(3) volume) was placed at the center of the phantom. We recorded the temporal variation of ionization current during the entire treatment. Measurements were made for 3 test cases and 7 clinical cases. The average transit time between successive shots, during which the APS unit was moving the phantom for repositioning the shot coordinates, was 20.5 s for 9 cases. The average dose rate, which was measured at the center of the phantom and at a point outside the shot location, was 0.36 +/- 0.09 cGy/min when the beam output was approximately 3.03 Gy/min for the 18-mm collimator helmet. Hence, the additional intracranial radiation dose during the APS-driven head repositioning between two successive shots (or APS transit dose) was 0.12 +/- 0.050 cGy. The APS transit dose was independent of the helmet size and the position of shots within the phantom relative to the measurement point. The head repositioning with the APS system adds a small but not negligible dose to the dose expected for the manual repositioning method.
Medical Physics, 2019
Cone beam computed tomography (CBCT) imaging has been implemented on the Leksell Gamma Knife® Icon TM for assessing patient positioning in mask-based Gamma Knife radiosurgery. The purpose of this study was to evaluate the performance of the CBCTbased 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 4 marks from their preset values are 0.087 mm, 0.085 mm, 0.095 mm, 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 mm, 0.27 mm, 0.14 mm, 0.32º, 0.19º, 0.31º from the manual setup. The corresponding maximum differences are 0.41 mm, 0.33 mm, 0.29 mm, 0.45º, 0.31º, and 0.43º respectively. Compared to the treatment plan using the 2% & 1 mm criteria, the Accepted Article This article is protected by copyright. All rights reserved. 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. Conclusion: The CBCT imager and the image registration algorithm can reproduce phantom position with less than 0.5mm/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.
Journal of radiosurgery and SBRT, 2016
This work evaluates the precision and characteristics of the trigger level of the vacuum surveillance system of eXtend™ on Gamma Knife Perfexion and the effect of the potential displacement on the dose distribution. A total of 20 individually moulded mouthpieces based on human dental models were used to measure translational shift and rotation until the vacuum surveillance of eXtend interrupted the irradiation. The positional accuracy of the movement was 0.01 mm using a computerized numerically controlled positioning system. Rotation was introduced by peripheral pressure in superior or inferior direction on the mould and was measured with a digital inclinometer. In 10 patients with a large brain metastasis the effect of a potential displacement of the centre of the target was recalculated. Two out of the 10 targets were located near the optic nerve and chiasm. In addition, the potential displacement of the chiasm and the optic nerve due to rotation based on their distance to the cen...
A comparison of the gamma knife model C and the Automatic Positioning System with Leksell model B
Journal of Neurosurgery, 2005
Object.The authors sought to compare the quality of treatment planning, radiation protection, and the time taken for treatment in the Leksell gamma knife model B with that using the model C Automatic Positioning System (APS).Methods.Data were obtained in 463 patients treated with the B model and 518 patients treated with the C model. Data were analyzed in patients in whom the following diagnoses had been made: vestibular schwannoma, pituitary adenoma, meningioma, solitary metastasis, and other benign and malignant solitary tumors. Patients with arteriovenous malformations, ocular lesions, and functional diagnoses were excluded from this study.Conclusions.With the C model there was a better conformity for most treated targets, such as vestibular schwannomas (p = 0.005) and meningiomas (p = 0.015). The level of radiation exposures to personnel was significantly decreased when using the model C (p < 0.001). There was no significant difference in radiation exposure of extracranial st...
Journal of neurosurgery, 2012
The Extend system for the Gamma Knife Perfexion makes possible multifractional Gamma Knife treatments. The Extend system consists of a vacuum-monitored immobilization frame and a positioning measurement system used to determine the location of the patient's head within the frame at the time of simulation imaging and before each treatment fraction. The measurement system consists of a repositioning check tool (RCT), which attaches to the Extend frame, and associated digital measuring gauges. The purpose of this study is to evaluate the performance of the Extend system for patient repositioning before each treatment session (fraction) and patient immobilization between (interfraction) and during (intrafraction) each session in the first 10 patients (36 fractional treatments) treated at the University of Virginia. The RCT was used to acquire a set of reference measurements for each patient position at the time of CT simulation. Repositioning measurements were acquired before each f...
Progress in Medical Physics
Radiotherapy patients should maintain their treatment position as patient setup is very important for accurate treatment. In this study, we evaluated patient setup error quantitatively according to Cone-Beam Computed Tomography (CBCT) Gamma Density Analysis using Mobius CBCT. The adjusted setup error to the QUASAR™ phantom was moved artificially in the superior and lateral direction, and then we acquired the CBCT image according to the phantom setup error. To analyze the treatment setup error quantitatively, we compared values suggested in the CBCT system with the Mobius CBCT. This allowed us to evaluate the setup error using CBCT Gamma Density Analysis by comparing the planning CT with the CBCT. In addition, we acquired the 3D-gamma density passing rate according to the gamma density criteria and phantom setup error. When the movement was adjusted to only the phantom body or 3 cm diameter target inserted in the phantom, the CBCT system had a difference of approximately 1 mm, while Mobius CBCT had a difference of under 0.5 mm compared to the real setup error. When the phantom body and target moved 20 mm in the Mobius CBCT, there are 17.9 mm and 13.5 mm differences in the lateral and superior directions, respectively. The CBCT gamma density passing rate was reduced according to the increase in setup error, and the gamma density criteria of 0.1 g/cc/3 mm has 10% lower passing rate than the other density criteria. Mobius CBCT had a 2 mm setup error compared with the actual setup error. However, the difference was greater than 10 mm when the phantom body moved 20 mm with the target. Therefore, we should pay close attention when the patient's anatomy changes.
Experimental Dosimetric Checkup Under Positioning Errors According to Gamma Criterion
2018
Whereas the number of clinics benefiting from the option to provide radiotherapy treatments using modulated intensity techniques, detrimental to the 3D conformal technique, is significantly increasing, the need to ensure a high-quality treatment plan is also increasing; mainly using the gamma criterion. In order for a treatment plan to pass the gamma criterion analysis, at least 95% of the measured items should pass the gamma analysis for the 3%/3 mm criterion, and at least 90% for the 2%/2mm criterion [1]. This study aims at reviewing the impact of positioning errors in gamma criterion analysis (3%/3mm) on all its 3 axes (longitudinal, lateral and vertical), depending on the complexity of the PTV.
A comparison of four skull models for independent dose calculations for Gamma Knife® PERFEXION™
Medical Physics, 2011
It is recommended to have a method for independently verifying planned doses in stereotactic radiosurgery. The problem is one of how to model the geometry of a skull sampled by a limited number of points and how to subsequently calculate numerous attenuation pathlengths through the modeled skull. While methods of verification have been previously published for model B and C Gamma Knife® units, the aims of the current work were to apply the principles of these previously published techniques for the verification of plans for Gamma Knife® PERFEXION™, to present a new method of verification, and to compare all methods in terms of their agreement with GammaPlan®. Methods: Four algorithms were implemented: the previously published spherical approximation method ͑SAM͒ and bubble helmet skull ͑BHS͒, plus a modified BHS named interpolated BHS ͑IBHS͒ and a newly developed variable radius SAM ͑VRSAM͒. Reference point doses calculated by the four algorithms were compared to those reported by GammaPlan® for 54 simple test plans and for 35 targets in 20 recent patient plans. Results: For test plans, the mean ͑standard deviation͒ discrepancies against GammaPlan®-reported doses were 0.3͑1.3͒%, 0.3͑1.3͒%, Ϫ1.6͑3.4͒%, and Ϫ0.4͑1.0͒% for SAM, VRSAM, BHS, and IBHS, respectively. For patient plans both the VRSAM and IBHS showed insignificant ͑p = 0.22 and p = 0.50͒ discrepancies against GammaPlan® of 0.38͑1.86͒% and Ϫ0.11͑1.86͒%, respectively. More significant discrepancies against GammaPlan® ͑p Ͻ 0.0001͒ of 2.64͑2.98͒% and Ϫ4.43͑3.39͒% were observed for the SAM and BHS. Conclusions: The SAM can lead to large discrepancies against GammaPlan® when a sphere is a poor approximation of the true skull surface, and in peripheral locations can lead to nonreal solutions to the attenuation pathlength calculations. While the BHS does not suffer the same geometric assumptions of the SAM, it can underestimate dose for peripherally located shots. The IBHS exhibits better agreement with GammaPlan® than does the BHS, but requires two-dimensional interpolation that was found to be impractical to implement in the Excel-based software used in the current work. Combining aspects of both the previously published SAM and BHS algorithms, the newly presented VRSAM exhibits comparable results to the IBHS but without the need for interpolation and is therefore considered the preferred technique of the four implemented.
Applied Radiation and Isotopes, 2004
A flexible technique for positioning patients in fixed orientation radiation fields such as those used in neutron capture therapy (NCT) has been developed. The positioning technique employs reference points marked on the patient in combination with a 3D digitizer to determine the beam entry point and a template fitted to the patient's head is used to determine the proper beam orientation. A coordinate transformation between the CT image data and reference points on the patient determined by a least squares algorithm based on singular value decomposition is used to map the beam entry point from the planning system onto the patient. The technique was validated in a phantom study where the mean error in entry point placement was 1.3 mm. Five glioblastoma multiforme patients have been treated with NCT using this positioning technique.