Patent Number: 053176170
Section: claims

1. An apparatus for selectively positioning the x-ray detector array of an apparatus for acquiring CT scans in the field of x-ray radiation produced by a radiation therapy simulator comprised of an x-ray radiation source, on x-ray table and an image intensifier tube so that the simulator is capable of being used for both therapy planning and computed tomography scanning comprising: a tray for mounting over the image intensifier tube of the radiation therapy simulator;  means mounted to said 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 x-ray radiation produced by the radiation source of the simulator for use of the simulator for treatment planning purposes to a second position in the tray within the field of x-ray radiation produced by the radiation source for use of the simulator as a CT scanner; and  a cover for closing said tray to form a substantially closed box with a height dimension substantially smaller than the width and depth dimensions thereof for fitting over the image intensifier tube and under the x-ray table of the simulator, the portion of said cover above the image intensifier tube of the simulator being comprised of radiolucent material.  mounting a box formed of a cover and tray over the image intensifier tube and below the table of the radiation therapy simulator;  positioning a detector array in the box within the field produced by the x-ray source for producing output readings proportional to the degree of attenuation of the field by the target object;  rotating the x-ray source and the image intensifier tube, having the box mounted thereto, around the target object while storing the output readings of the detector array to memory to obtain attentuation data at a plurality of angles of rotation; and  stopping the rotation of the x-ray source and image intensifier tube in the event of a change in the 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. 2. The apparatus of claim 1 wherein said detector array moving means comprises a caddy slidably positioned in said tray and adapted for mounting the detector array thereto. 3. The apparatus of claim 2 wherein said detector array moving means additionally comprises electrically-controlled drive means for selectively moving said caddy from said first position to said second position. 4. The apparatus of claim 3 additionally comprising a limit switch for turning said drive means off after said caddy, having the detector array mounted thereto, move to said second position. 5. The apparatus of claim 3 additionally comprising circuitry for activating said drive means to move said caddy, having the detector array mounted thereto, to said second position when the simulator is operated as a CT scanner. 6. The apparatus of claim 3 wherein said cover is secured to means for detecting a change in the height of the box formed by said cover and said tray. 7. The apparatus of claim 6 additionally comprising circuitry for stopping the operation of the simulator when said change detecting means detects a change in the height of the box formed by said cover and said tray. 8. The apparatus of claim 1 additionally comprising means for stopping operation of the simulator when either the height dimension of the box formed by said tray and said cover changes or when the flat surfaces of said tray and said cover are not positioned in substantially parallel planes. 9. The apparatus of claim 1 wherein said cover is comprised of a radiolucent material. 10. The apparatus of claim 1 additionally comprising an x-ray film cassette holder mounted on said cover. 11. The apparatus of claim 10 wherein said cassette holder is mounted to said cover on a turntable for rotating said cassette holder to facilitate insertion of a film cassette therein. 12. The apparatus of claim 10 wherein said cassette holder is comprised of radiolucent material. 13. A method for utilizing a radiation therapy simulator comprised of an x-ray source, table for supporting a target object in the field of radiation produced by the x-ray source, and image intensifier tube for acquiring computed tomography scans comprising the steps of: 14. The method of claim 13 additionally comprising moving the detector array out of the radiation field when a change in the relative positions of the cover and the tray is sensed.