A comparison of the gamma knife model C and the Automatic Positioning System with Leksell model B (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.
Journal of applied clinical medical physics / American College of Medical Physics, 2010
The GammaPlan treatment planning system does not account for the leakage and scatter dose during APS repositioning. In this study, the dose delivered to the target site and its periphery from the defocus stage and intershot couch transit (couch motion from the focus to defocus position and back) associated with APS repositioning are measured for the Gamma Knife model 4C. A stereotactic head-frame was attached to a Leksell 16 cm diameter spherical phantom with a calibrated ion chamber at its center. Using a fiducial box, CT images of the phantom were acquired and registered in the GammaPlan treatment planning system to determine the coordinates of the target (center of the phantom). An absorbed dose of 10 Gy to the 50% isodose line was prescribed to the target site for all measurements. Plans were generated for the 8, 14 and 18 mm collimator helmets to determine the relationship of measured dose to the number of repositions of the APS system and to the helmet size. The target coordin...
The clinical utilization of stereotactically delivered radiation for tissue ablation continues to increase in breadth and scope within the medical community. There are several commercially available systems capable of delivering stereotactic radiation treatments; each platform has unique capabilities and limitations. The Gamma Knife was the first commercially developed system and is currently the most widely utilized stereotactic radiosurgery system for intracranial treatments. The CyberKnife® Radiosurgery System, the first image-guided robotic system enabling whole-body stereotactic radiosurgery, has rapidly become the most widely used system for extracranial radiosurgery. Both the Gamma Knife and CyberKnife are available and used at our institution, containing St. Joseph’s Hospital and Barrow Neurological Institute (BNI), for a variety of clinical conditions. The complementary use of these two distinct treatment platforms allows for meaningful objective comparisons and contrasts t...
Gamma Knife radiosurgery with CT image‐based dose calculation
Journal of Applied Clinical Medical Physics, 2015
The Leksell GammaPlan software version 10 introduces a CT image‐based segmentation tool for automatic skull definition and a convolution dose calculation algorithm for tissue inhomogeneity correction. The purpose of this work was to evaluate the impact of these new approaches on routine clinical Gamma Knife treatment planning. Sixty‐five patients who underwent CT image‐guided Gamma Knife radiosurgeries at the University of Pittsburgh Medical Center in recent years were retrospectively investigated. The diagnoses for these cases include trigeminal neuralgia, meningioma, acoustic neuroma, AVM, glioma, and benign and metastatic brain tumors. Dose calculations were performed for each patient with the same dose prescriptions and the same shot arrangements using three different approaches: 1) TMR 10 dose calculation with imaging skull definition; 2) convolution dose calculation with imaging skull definition; 3) TMR 10 dose calculation with conventional measurement‐based skull definition. ...
2023
Radiosurgery is a well-established available technique for treating many diseases and indications. Planning quality assessment is a crucial step in the procedure itself and outcome probabilities; either control or complication probability. Several physical indices and methodology have been developed to describe any plan. Accordingly, plan quality and outcome could be compared with other plans. In current study, the aim was to compare two plans with different isodose line using radiobiological model, tumor control probability (TCP), normal tissue complication probability (NTCP) and plan's physical indices. Material and Methods: The cross-sectional study included 20 patients (5 male and 15 female) with median age of 44 years (21-66) and presented with radiologically diagnosed meningioma. Two radiosurgical forward plans were applied with same marginal dose of 12Gy at two different isodose lines of 50% and 75% isodose alternatively using Leksell Gamma Plan of single session GKS. Dose-Volume Histogram (DVH) was imported to MATLAB to compute TCP, NTCP values at 5 years for each plan, and physical indices such as coverage, selectivity, conformity, heterogeneity, and gradient indices. Results: Median target irradiated volume was 7.5 cm 3 (0.588-23.72). TCP was significantly higher in the plan using 50% isodose line for the marginal dose than that using 75% isodose line (95.05%, 49.44%, p<0.05, Independent Samples t-Test). Brainstem and optic apparatus NTCPs were very low 0.01% (0-0.045%) in the former plan and zero in the later one (p =0.001, Mann-Whitney test). Conclusion: Radiobiological models and physical indices could be used for the optimum plan selection of GKS.
Dosimetrical evaluation of Leksell Gamma Knife 4C radiosurgery unit
Polish Journal of Medical Physics And Engineering, 2011
A number of experiments was performed using standard protocols, in order to evaluate the dosimetric accuracy of Leksell Gamma Knife 4C unit. Verification of the beam alignment has been performed for all collimators using solid plastic head phantom and Gafchromic TM type MD-55 films. The study showed a good agreement of Leksell Gammaplan calculated dose profiles with experimentally determined profiles in all three axes. Isocentric accuracy is verified using a specially machined cylindrical aluminium film holder tool made with very narrow geometric tolerances aligned between trunnions of 4 mm collimator. Considering all uncertainties in all three dimensions, the estimated accuracy of the unit was 0.1 mm. Dose rate at the centre point of the unit has been determined according to the IAEA, TRS-398 protocol, using Unidose-E (PTW-Freiburg, Germany) with a 0.125 cc ion chamber, over a period of 6 years. The study showed that the Leksell Gamma Knife 4C unit is excellent radiosurgical equipment with high accuracy and precision, which makes it possible to deliver larger doses of radiation, within the limits defined by national and international guidelines, applicable for stereotactic radiosurgery procedures.
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...
Gamma Knife Radiosurgery: An Overview of Physics, Chemistry, Biology and Neuro-medicine
Journal of Bangladesh College of Physicians and Surgeons, 1970
The gamma knife is a highly specialized treatment unit thatprovides an advanced sophisticated stereotactic approachto treatment of tumour and vascular malformations withinthe internal structure of the head. The gamma knife deliversa single high dose of radiation emanating from 201 cobalt-60 unit sources. All 201 beam simultaneously intersect atthe same time in a pre-defined location. The treatmentplanning system for gamma knife radiosurgery has beendeveloped using nonlinear programming techniques. Thesystem optimizes the shot sizes, location and weights forgamma knife treatments. Open stereotactic technique in the1990’s was essential for the treatment of a number offunctional conditions and cystic space occupying lesions.It has an important part to play in the investigation oftumours and can help to increase the number which areaccessible to treatment. It can be employed to guide notonly solid instruments but also ionizing irradiation to “masslesion– targets”. It is just this combin...
Treatment planning for gamma knife radiosurgery with multiple isocenters
International Journal of Radiation Oncology Biology Physics, 1990
Many arteriovenous malformations and tumors suitable for radiosurgical treatment have non-spherical or irregular shapes. Forty-eight percent of the first 156 patients treated with the gamma unit at the University of Pittsburgh required treatment with two or more isocenters to optimize dose distributions. Dose distributions for combining gamma knife treatments to two or more isocenters were systematically investigated. High speed computerized dosimetry was performed using specially developed software and dose distributions were confirmed with film densitometry. We have developed guidelines for treatment to two or more isocenters which help reduce treatment planning time, and facilitate selection of treatment doses and optimum dose distributions. These guidelines include maintaining an account of the distances between all isocenters, using a catalogue of sample two-isocenter isodose plans, comparing dose volume histograms, and calculating complication probabilities using the integrated logistic formula.