Diagnostic CT Scanner Research Articles

A model for the physical optimization of external beam radiotherapy

A model for optimizing conformal radiotherapy dose distributions was developed based on the analogy between rotational radiotherapy and single photon emission computed tomography image reconstruction. The optimization model predicts that a large number of intensity modulated beam profiles are required to maximize conformation of the dose distribution to the dose prescription—a solution not practically feasible using early 1990s treatment delivery technology. A new method of treatment realization similar to spiral CT scanning called tomotherapy is described. The tomotherapy unit would incorporate a diagnostic CT scanner for acquiring tomographic images prior to and during a treatment for optimized treatment planning and treatment verification, respectively. The tomotherapy concept represents the first truly integrated approach to optimized treatment planning, delivery, and verification of external beam radiotherapy and could significantly advance the state-of-the-art in radiotherapy.

Image quality of an analog radiation therapy simulator-based tomographic scanner.

The spatial resolution and noise level of images produced by a commercial analog tomographic scanner have been measured and compared to those of images reconstructed digitally from projections from the same detector. The full width at half maximum of the line spread function was 3.6 mm for images from the analog scanner and 1.1 mm for the digitally reconstructed images. The standard deviation of the CT numbers over a 10-cm2 circular area at the center of a large water phantom, calculated as a percentage of the linear attenuation coefficient of water, was 3.5% for the analog images, 15.4% for high-resolution digital images, and 3.2% for digital images reconstructed using a convolution filter which reduced the resolution to that of the analog images. The data contributing to each digital image were fewer than those contributing to each analog image by a factor of 10. The noise level did not depend on tube current in either the analog or the digital images. The utility of this analog device in radiation therapy planning will depend upon whether errors in contour localization resulting from transferring data from diagnostic CT scanners exceed the errors due to its poorer image quality.

Development of a computed tomographic scanner for radiation therapy treatment planning.

The authors describe a low-cost CT scanner integrated with a radiotherapy simulator and designed for treatment planning. The standard rotational gantry and x-ray tube of the simulator are used with a multiwire xenon lonization chamber and simple current-proportional readout system to measure patient attenuation, avoiding problems associated with diagnostic CT scanners in treatment planning. Although design constraints limit performance, software compensation techniques have reduced artifacts and given satisfactory images.