X-ray or gamma ray systems or devices – Photographic detector support – Sheet film cassette
Reexamination Certificate
2000-08-30
2002-05-28
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Photographic detector support
Sheet film cassette
C378S185000
Reexamination Certificate
active
06394649
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to portal radiography using radiation therapy treatment beams. More particularly, it relates to an assembly useful for radiation oncology portal imaging system using radiographic films and intensifying screens, and to a method of using it.
BACKGROUND OF THE INVENTION
In conventional medical diagnostic imaging, the object is to obtain an image of a patient's internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a dual-coated radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the dual-coated radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are shown in U.S. Pat. No. 4,425,425 (Abbott et al), U.S. Pat. No. 4,425,426 (Abbott et al), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Kelly et al) and U.S. Pat. No. 4,900,652 (Kelly et al), U.S. Pat. No. 5,252,442 (Tsaur et al), and
Research Disclosure,
Vol. 184, August 1979, publication 18431.
Radiation oncology is the branch of radiology directed to radiation treatment of cancers. Much of the work is called teletherapy, that is the use of powerfill, high-energy X-ray machines (often linear accelerators) to irradiate the cancerous tissues. The goal of the treatment is to cure the patient by selectively irradiating the cancer with sufficiently high dosage to destroy it, yet minimizing the radiation impacting adjacent normal tissues.
Such treatments are commonly made using high energy X-rays (generally 4000 to 25,000 kVp). The X-ray beams are carefully mapped for intensity and energy. The patient is carefully imaged using a conventional diagnostic X-ray machine and/or a CT scanning machine and/or an MRI scanning machine to accurately locate features in the patient's anatomy. With this information, a dosimetrist determines where and for how long the treatment X-rays should be directed. The dosimetrist uses a computer to predict the radiation dose necessary for the patient's condition. This may lead to some normal tissues being too greatly exposed. The dosimetrist will then use one or more “blocks” or shields to block radiation from reaching the patient's normal tissues. These “blocks” are custom shaped for each patient and are typically made from thick pieces of lead.
Portal radiography is used to provide images to position and confirm radiotherapy in which the patient is given a dose of high energy X-radiation (from 4 to 25 MVp) through a “port” in a radiation shield. The object is to line up the port with a targeted tumor so it receives a cell-killing dose of X-radiation. In localization imaging the portal radiographic element is briefly exposed to the X-radiation passing through the patient with the shield removed and then with the shield in place. Exposure without the shield provides a faint image of anatomical features that can be used as orientation references near the target (e.g., tumor) area while the exposure with the shield superimposes a second image of the port area. The exposed localization radiographic element is quickly processed to produce a viewable image and confirm that the port is in fact properly aligned with the intended anatomical target. During the above procedure patient exposure to high energy X-radiation is kept to a minimum. The patient typically receives less than 20 RADs during this procedure.
Thereafter, before the patient is allowed to move, a cell-killing dose of X-radiation is administered through the port. The patient typically receives from 50 to 300 RADs during this step. Since any movement of the patient between the localization exposure and the treatment exposure can defeat the entire alignment procedure, the importance of minimizing the time elapsed during the element processing cycle is apparent. Reducing this time by even a few seconds is highly beneficial.
A second, less common form of portal radiography is the verification of the location of the cell killing exposure. Again, the object is to record enough anatomical information to confirm that the cell killing exposure was properly aligned with the targeted anatomy.
It is appreciated that the large differences in exposure times that distinguish localization and verification imaging have up to the date of this invention precluded the successful use of a single portal radiographic element to serve both applications.
Both localization and verification portal imaging have suffered from very poor image quality. Anatomical features are often faint, barely detectable or even non-detectable. This has severely restricted reliance on portal radiography.
Although excellent radiographic imaging capabilities have been realized in medical diagnostic imaging, there are fundamental differences in the imaging physics that distinguish and render nonanalogous diagnostic and portal radiographic imaging. In diagnostic imaging X-radiation photon energy of up to 140 kVp is in part absorbed within the patient and in part passed through to be absorbed in a fluorescent intensifying screen to generate light that exposes the radiographic element.
In portal imaging the multi-MVp X-radiation in part passes through the patient unabsorbed and is in part absorbed creating a secondary electron emission. A front metal intensifying screen is relied upon to intercept and absorb the secondary electron emission. This lowers minimum density and significantly enhances image sharpness. Image intensification (raising maximum density and contrast) is achieved by absorbing X-radiation and transmitting to the radiographic element electrons that are thereby generated. The much higher capability of the radiographic element to absorb electrons as compared to X-radiation produces image intensification. Besides supplying electrons that are relied upon to expose the radiographic element, the front intensifying screen further contributes to image sharpness by transmitting to a much lesser extent electrons generated by obliquely oriented (that is scattered) X-radiation that it receives.
In addition to the front metal intensifying screen, which is always present, a back metal intensifying screen can be employed to provide an additional source of electrons for radiographic element exposure.
Portal imaging assemblies can be grouped into two categories. In the first category, the assembly includes one or two metal plates and a photographic silver halide film that is designed for direct exposure to X-rays or electrons. Two such films are commercially available from Eastman Kodak Company as KODAK X-RAY Therapy Localization (XTL) Film and KODAK X-RAY Verification (XV) Film. Such direct X-ray exposure assemblies are illustrated in
FIG. 1
(described in more detail below). The advantage of such assemblies is that their contrast is very low so that a wide range of exposure conditions provides useful images. However, due to the high-energy radiation used to produce portal images, the subject contrast is also very low. Coupled with the low contrast of the image receptor system, the final image contrast is low and the images are difficult to read with needed accuracy.
The second portal imaging assembly uses a radiographic photographic silver halide film containing fine grain silver halide emulsions, one or two fluorescent (or phosphor) screens (or intensifying panels) and one or two metal plates. One such assembly is illustrated in
FIG. 2
(described in more detail below). Although the assembly in
FIG. 2
shows only one metal plate, other assemblies can have both front and back metal plates. Because a significant portion of the film's exposure comes from the
Moore William E.
Steklenski David J.
Eastman Kodak Company
Ho Allen C.
Kim Robert H.
Tucker J. Lanny
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