Radiation imagery chemistry: process – composition – or product th – Luminescent imaging
Reexamination Certificate
2002-11-07
2003-06-24
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Luminescent imaging
C430S428000, C430S497000, C430S502000, C430S509000, C430S966000, C430S967000
Reexamination Certificate
active
06582874
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to radiography in which radiation is aimed at certain regions of a subject to provide therapy treatment. In particular, it is directed to a radiographic portal localization imaging film, to combinations of such films and intensifying screens, and to methods of use. This invention is useful in portal localization radiography.
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 provided by U.S. Pat. No. 4,425,425 (Abbott et al) and 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) 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, Item 18431.
Radiation oncology is a field of radiology relating to the treatment of cancers using high energy X-radiation. This treatment is also known as teletherapy, using powerful, high-energy X-radiation machines (often linear accelerators) to exposure the cancerous tissues (tumor). The goal of such treatment is to cure the patient by selectively killing the cancer while minimizing damage to surrounding healthy tissues.
Such treatment is commonly carried out using high energy X-radiation, 4 to 25 MVp. The X-radiation beams are very carefully mapped for intensity and energy. The patient is carefully imaged using a conventional diagnostic X-radiation unit, a CT scanner, and/or an MRI scanner to accurately locate the various tissues (healthy and cancerous) in the patient. With full knowledge of the treatment beam and the patient's anatomy, a dosimetrist determines where and for how long the treatment X-radiation will be directed, and predicts the radiation dose to the patient. Usually, this causes some healthy tissues to be overexposed. To reduce this effect, the dosimetrist provides one or more custom-designed “blocks” or shields of lead around the patient's body to absorb X-radiation that would impact healthy tissues.
To determine and document that a treatment radiation beam is accurately aimed and is effectively killing the cancerous tissues, two types of imaging are carried out during the course of the treatment. “Portal radiography” is generally the term used to describe such imaging.
The first type of portal imaging is known as “localization” imaging in which the portal radiographic film is briefly exposed (usually less than 10 seconds) to the X-radiation passing through the patient with the lead shields removed and then with the lead shields in place. Exposure without the lead shields provides a faint image of anatomical features that can be used as orientation references near the targeted feature while the exposure with the lead shields superimposes a second image of the port area. This process insures that the lead shields are in the correct location relative to the patient's healthy tissues. Both exposures are made using a fraction of the total treatment dose, usually 1 to 4 monitor units out of a total dose of 45-150 monitor units. Thus, the patient receives less than 20 RAD's of radiation.
Silver halide emulsions generally used for “localization” imaging contain relatively large silver halide grains, usually as high as 0.7 &mgr;m when exposed directly and from 0.25 to 0.4 &mgr;m when used with a fluorescent intensifying screen, because of the limited exposure to X-radiation.
If the patient and lead shields are accurately positioned relative to each other, the therapy treatment is carried out using a killing dose of X-radiation administered through the port. The patient typically receives from 50 to 300 RAD's during this treatment. Since any movement of the patient during exposure can reduce treatment effectiveness, it is important to minimize the time required to process the imaged films.
A second, less common form of portal radiography is known as “verification” imaging to verify the location of the cell-killing exposure. The purpose of this imaging is to record enough anatomical information to confirm that the cell-killing exposure was properly aligned with the targeted tissue. The imaging film/cassette assembly is kept in place behind the patient for the full duration of the treatment (at least 30 seconds). Verification films have only a single field (the lead shields are in place) and are generally imaged at intervals during the treatment regime that may last for weeks. Thus, it is important to insure that proper targeted tissue and only that tissue is exposed to the high level radiation because the levels of radiation are borderline lethal.
Portal radiographic imaging film, assembly and methods are described, for example, in U.S. Pat. No. 5,871,892 (Dickerson et al.) in which the same type of radiographic element can be used for both localization and portal imaging.
Portal verification radiographic elements are described in U.S. Pat. No. 5,952,147 (Dickerson et al.) for use in verification imaging using exposures of 30 seconds or more. Silver halide emulsions used for verification imaging generally need to contain “fine” grains so the emulsion speed is lowered for the very high exposure times and energies. However, such “fine” grains usually provide poorer image tone.
Portal imaging assemblies can be grouped into two categories. The first type of assemblies includes one or two metal plates and a radiographic silver halide film that is designed for direct exposure to X-radiation. Two such films that are commercially available are KODAK X-ray Therapy Localization (XTL) Film and KODAK X-ray Therapy Verification (XV) Film. Each of these films is generally used with a single copper or lead plate. They have the advantage of having low contrast so that a wide range of exposure conditions can be used to produce useful images. However, because high energy X-radiation is used to produce therapy portal images, the contrast of the imaged tissues (target tissues) is also very low. Coupled with the low contrast of the imaging system, the final image contrast is very low and difficult to read accurately.
The second type of portal imaging assemblies includes a fluorescent intensifying screen and a silver halide radiographic film. These assemblies include one or two metal plates, one or two fluorescent intensifying screens, and a fine grain emulsion film. Because a significant amount of the film's exposure comes from the light emitted by the fluorescent screen(s), it is possible to use films that provide high contrast images. Thus, these imaging assemblies typically provide images having contrast 3.5 times higher than those direct imaging assemblies noted above do. However, the photospeed obtained with both types of assemblies is about the same. Moreover, the images from this second type of assemblies have much higher “NEQ”, show clearer structure definition and are easier to read.
However, these imaging assemblies present some problems. Due to their high contrast images and the variations in patient treatment dosages, patient tissue conditions (thickness), and exposing equipment, it is more difficult to obtain correct exposures. The images are either too light or too dark. Exposure can be controlled by adjusting the so-called “air gap” distance between the patient and the imaging system. Unfortunately, many therap
Dickerson Robert E.
Moore William E.
Schilling Richard L.
Tucker J. Lanny
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