1. Field of the Invention
The present invention relates to a radiation imaging and therapy apparatus for obtaining a radiation image of a breast and having a therapy function of applying radiation to an affected part in the breast.
2. Description of a Related Art
Recent years, an image-guided radiation therapy (IGRT) apparatus combining a tomographic imaging apparatus and a radiation therapy apparatus has been developed. Thereby, a radiation application method can be planned based on a three-dimensional (3D) image near an affected part, and radiation therapy for applying radiation can be performed according to the plan.
For example, Japanese Patent Application Publication JP-A-9-192245 discloses a radiation therapy system as shown in FIG. 12. The radiation therapy system includes a bed movably supported in a direction in parallel with the reference surface, an imaging apparatus (X-ray CT apparatus) that can image a part for therapy of an object to be inspected on the bed, a positioning apparatus for positioning the part for therapy from the image obtained by the imaging apparatus, and a radiation therapy apparatus for performing therapy by applying radiation to the positioned part for therapy. The imaging apparatus, the positioning apparatus, and the radiation therapy apparatus are accommodated together in one room, and a patient as the object undergoes therapy while staying on the bed because the bed sequentially moves to the locations of the respective apparatuses.
However, the image-guided radiation therapy apparatus can be used for all body organs as targets of examinations, and there is a problem that a contrast agent is necessary for an examination of breast cancer because an X-ray having high penetrating power generated by an X-ray tube voltage equal to or more than 100 kV for image formation is used. Further, since image-guided radiation therapy apparatus is used for a whole body as a target of examination, upsizing of the entire apparatus is unavoidable.
On the other hand, for the main purpose of detections and diagnoses of breast cancer, a radiation tomographic imaging apparatus for breast (mammography CT apparatus) that can obtain three-dimensional (3D) images has been developed. As an example of a mammography CT apparatus, U.S. Pat. No. 6,480,565 B1 discloses a device for producing a three-dimensional tomographic mammography image of a breast of a patient. The device disclosed in U.S. Pat. No. 6,480,565 B1 comprises: a gantry frame; at least one motor for moving the gantry frame to form a data acquisition geometry; a source of radiation attached to the gantry frame to move with the gantry frame; a flat panel detector attached to the gantry frame to move with the gantry frame, the flat panel detector being disposed in a path of the radiation; and a support on which the patient rests while the mammography projection images are taken, the support supporting the patient such that the breast is disposed between the source of radiation and the flat panel detector; the support comprising a table on which the patient lies while the mammography projection images are taken; wherein the at least one motor moves the gantry frame so that the flat panel detector takes a volume scan of the breast; and wherein the table has two breast holes for both of the patient's breasts. For imaging a tumor mass or calcification in the breast, an X-ray with high energy has a small ratio of transmission amount and the contrast of transmission image is weak, and therefore, an X-ray beam with low energy of about 25 kV to 50 kV is used.
When breast cancer detection is performed by using the device disclosed in U.S. Pat. No. 6,480,565 B 1, the patient rests face down on the table to allow two breasts to extend through the two breast holes, and one breast descends between the radiation source and the flat panel detector. The radiation source and the flat panel detector perform radiation imaging at each predetermined angular position while rotating together around a rotational axis, and thereby, the flat panel detector obtains radiation images of the breast in plural directions. The image signals obtained by the flat panel detector are transmitted to an image reconstruction and processing module. The image reconstruction and processing module three-dimensionally reconstructs the obtained radiation images to create a radiation tomographic image of the breast. Since the radiation tomographic image of the breast is a 3D image, a focus part at the rear side of the tissues such as mammary gland can be detected.
Accordingly, in the image-guided radiation therapy apparatus for performing radiation therapy for breasts, it is conceivable that the mammography CT apparatus is used in place of the imaging apparatus that can obtain radiation projection images in plural directions. However, when the mammography CT apparatus and the radiation application therapy apparatus are combined, it is difficult to reproduce the affected part location in the radiation application therapy apparatus for accurate therapy of the affected part in the breast, which has been recognized by using the mammography CT apparatus.