Verification of radiosurgery target point alignment with an electronic portal imaging device (EPID).
ABSTRACT A procedure has been developed using an electronic portal imaging device (EPID) to verify that the center of a patient's lesion is aligned with the center of a treatment cone prior to treatment in a linac-based stereotactic radiosurgery procedure. The coordinates of the lesion center are set on the Brown-Roberts-Wells phantom base using a target simulator. A 3 mm tungsten ball, mounted on the target simulator, is used as the reference point for the planned isocenter. The target simulator is then attached to an adapter mounted on the linac couch, and an EPID image of the simulated target is acquired. The center of the circular-shaped radiation field is calculated from the centroid of the segmented EPID image, and the center of the tungsten ball is identified by an automated computer search algorithm. A summation filter is used to find the position of the lowest radiation intensity coincident with the center of the ball. The alignment error is defined as the difference between the center of the radiation field and the center of the ball. The accuracy of this method was tested and found to be within 0.2 mm. The advantage of the EPID-based procedure is that it can give quantitative offset values quickly for immediate readjustment. We have found that the method is also a convenient tool for testing room laser alignment and the accuracy of the treatment cones.
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ABSTRACT: The first step in the project is to develop the theoretical framework necessary for designing an analog prototype of the localizing transmitter. To date, much of the theoretical foundation is developed to characterize the design parameters of the system including the dipole antenna power support. The design parameters for the system are identified as: the dipole and transmitter inductor radii, inductance, capacitance, and magnetic field strength. Using the size constraints imposed by the implant transmitter, the time scales and associated transmitter field strengths are found to be plausible for a clinical environment. This demonstrates that the concept is possible in terms of physical properties of the system. With this analysis, further details of the system can be derived and an analog system can be created for experimental verification. Additional measurements will be used to supplement theory as empirical models to increase the prediction accuracy for creating a detailed transmitter design.02/2005;
Article: Theoretical foundation for real-time prostate localization using an inductively coupled transmitter superconducting quantum interference devicesJournal of Applied Clinical Medical Physics 04/2004; · 1.29 Impact Factor