Patent Number: 053176170
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for mounting the detector array of a CT (computed tomography) scanner to a conventional radiation therapy simulator (RTS) for use of the simulator to produce scans without inhibiting the simulator's fluoroscope and plain film acquisition modes when scans are not being acquired. More specifically, the present invention is directed to a method and apparatus for use in connection with the CT scanner described in co-pending applications Ser. Nos. 07/718,544 and 07/850,346, both assigned to W. L. Systems, Inc. The invention described in that co-pending application is a method and apparatus for back projecting a CT scan using a conventional radiation therapy simulator without rendering the simulator incapable of being used for treatment planning purposes. The present invention facilitates that use by providing the method and apparatus for mounting the detector array of that apparatus to the simulator while still providing for the use of the simulator as a radiation therapy simulator. In that manner, the CT scanner is also used to enhance treatment planning. The method and apparatus of the present invention has the additional advantage of providing a safety override for the simulator to which the apparatus is mounted. Specifically, the apparatus stops the rotation of the gantry or movement of the fixture supporting the image intensifier tube of the simulator in the event that an object is encountered during rotation or other movement, thereby decreasing the likelihood of damage to the apparatus of the present invention, the simulator, or the encountered object. Other advantages, and the objects of the present invention will be apparent from the following detailed description of the preferred embodiment thereof. SUMMARY OF THE INVENTION The present invention can be summarized as an apparatus for selectively positioning the x-ray detector array of an apparatus for acquiring computed tomographic (CT) scans in and out of the field of radiation produced by the radiation source of a radiation therapy simulator so that the radiation source of the simulator is capable of being used for both radiation therapy planning and CT scanning. The apparatus comprises a tray for mounting over the image intensifier tube of a radiation therapy simulator and means mounted to the tray for selectively moving the detector array of an apparatus for acquiring CT scans from a first position in the tray outside of the field of radiation produced by the radiation source for use of the simulator for treatment planning purposes to a second position in the tray that is within the field of radiation produced by the radiation source for use of the simulator as a CT scanner. A cover is provided for closing the tray to form a substantially closed box with a height dimension substantially smaller than the width and depth dimensions of the box for fitting to the simulator over the image intensifier tube and under the x-ray table, the portion of the cover above the image intensifier tube of the simulator being comprised of radiolucent material. An x-ray film cassette holder, also comprised of radiolucent material, is mounted on the cover for holding the x-ray film cassette (and a grid, if the grid is being used) during use of the simulator for purposes other than CT scanning. Also provided is a method for utilizing a radiation therapy simulator for acquiring computed tomographic scans comprising the steps of mounting a box formed of a cover and a tray over the image intensifier tube and below the x-ray table of the radiation therapy simulator, positioning a detector array in the box within the field produced by the radiation source of the simulator for producing output readings proportional to the degree of attenuation of the field by a target object on the x-ray table, rotating the radiation source and the image intensifier tube, having the box mounted thereto, around the target object while storing the outputs of the detector array to memory to obtain attenuation data at a plurality of angles of rotation, and stopping the rotation of the radiation source and image intensifier tube, e.g., the gantry to which both are mounted, or movement of the image intensifier tube in the event of a change in distance from the radiation source to the cover of the box, the change being detected by sensing a change in the relative positions of the cover and the tray of the box.