A novel 2D/3D transformation for radiosurgery of ocular tumors: computer simulation and phantom validation

Noninvasive stereotactic radiosurgery with the Cyberknife system has been seen as a promising treatment platform for ocular tumors in clinical practice. However, due to the unpredictable eye movement during treatment, 6D skull tracking cannot account for random ocular tumor positions and therefore compromise treatment delivery precision. A real-time ocular tumor tracking system is highly desirable.We designed a novel “pupil tracking” approach that uses a derived 2D/3D transformation to relate the pupil’s 2D coordinate captured by a video camera in the image plane with the tumor’s 3D location in the CT space. To simulate and demonstrate the process of the 2D/3D transformation, a computer graphical model was created by using an interactive interface to mimic both tumor (size and location inside the eyeball) and eyeball (movement parameters). A mechanical phantom was also fabricated to validate the approach.Experimental data from computer simulation and phantom validation under the CT simulator were obtained. For eight testing points in the validation experiment by the mechanical phantom, the maximum root-sum-squared error (RSSE) of three coordinates (X, Y, Z) is less than 0.70 mm and the mean-squared error is 0.44 mm.Error analysis indicates that this pupil tracking technique has a potential application for radiosurgery of ocular tumors by the Cyberknife system

Limited value of cyclosporine A for the treatment of patients with uveitis associated with juvenile idiopathic arthritis

AIMS: Juvenile idiopathic arthritis (JIA) is often associated with severe chronic anterior uveitis (CAU), and immunosuppressive therapy may be required. In this study, the value of cyclosporine A (CsA) as monotherapy or as combination therapy for treating uveitis was studied in a large cohort of JIA children. METHODS: Multicentre retrospective study including 82 JIA children (girls n=60) suffering from unilateral or bilateral (n=55) CAU. The indication for CsA was active uveitis, although patients were on topical or systemic corticosteroids, MTX, or other immunosuppressive drugs. RESULTS: Inactivity of uveitis during the entire treatment period (mean 3.9 years) was obtained with CsA monotherapy in 6 of 25 (24%) patients, but more often when CsA was combined with the immunosuppressives (35/72 patients; 48.6%, P=0.037), or MTX (18/37 patients, 48.6%, P=0.065), which had already been given. With CsA (mean dosage 2.9 mg/kg), systemic immunosuppressive drugs and steroids could be reduced by >or=50% (n=19) or topical steroids reduced to <or=2 drops/eye/day (n=40) in selected patients. Pre-existing cystoid macular oedema did not resolve under CsA treatment in any of the patients. In nine patients (11%), CsA was discontinued because of systemic hypertension (n=1), elevated creatinine levels (n=3), or other adverse effects (n=5). CONCLUSIONS: These observations suggest that CsA has limited value as a second-line immunosuppressive drug for the treatment of JIA-associated CAU. The efficacy was better as the combination therapy in patients not responding to other immunosuppressives (eg, MTX) than the systemic monotherapy

A mechanical eyeball phantom for uveal melanoma radiosurgery by cyberknife

A treatment option for uveal melanoma has been investigated using the Cyberknife system, due to its advantage of real-time image guidance during therapy. However, unpredictable eyeball movement imposes challenges to the state-of-art technology. As a solution, we derived a 2D/3D transformation algorithm that is based on the pupil’s 2D coordinates captured by an optical tracking system to predict the tumor’s 3D positions in real-time. In order to validate our developed algorithm and other methods, a mechanical phantom that can simulate the eyeball’s movement is highly desirable.We designed a mechanical phantom that consists of a camera module, an eyeball module with an embedded “tumor", an eyeball holder module, and an eyeball moving module. All materials are made with acrylic or nylon plastics with the exception of the linear motion stages and the camera.In the calibration procedure, the phantom is scanned using a CT scanner. By using the recorded pupil’s coordinates and extracted tumor coordinates, the 2D/3D transformation model yields 0.39 ± 0.09 mm root-sum-squared error for five calibration positions between the actual 3D coordinates and the predicted coordinates. In the validation procedure, the eyeball is rotated to 11 different positions through the mechanical phantom. The 2D/3D transformation model yields 0.58 ± 0.27 mm root-sum-squared error for these positions between the Cyberknife-identified 3D coordinates and the predicted coordinates. The eyeball’s position can be controlled within millimeter accuracy.The designed mechanical phantom is suitable for validating image-guided radiosurgery methods. Further dynamic evaluations can confirm these methods for clinical applications