Patent Application
20080033286
As will be appreciated by those skilled in the art, there are several key considerations with respect to implanted fiducial markers. In particular, the markers must be clearly visible in the radiotherapy planning image study, typically accomplished by computer tomography (CT). The markers must also be clearly visible with the treatment machine imager, whether that be electronic portal imager, x-ray film or computerized radiograph. In addition the markers must not disrupt or distort any of the aforementioned imaging modalities. Since the markers are implanted in tissue or bone they must be formed biocompatible materials. Lastly, and perhaps most importantly, the markers must remain (relatively) stable with respect to the target location and to each other from the time of treatment planning imaging study and there after until treatment is completed in order to ensure that the target tissue can be precisely located with respect to all three dimensional directions.
Referring now to the various figures of the drawing wherein like reference characters refer to like parts, there is shown at 20 in
The marker 20 is of an overall “dumbbell” like shape and basically comprises a pair of end sections 22 and 24 which are each of a bulbous shape and which are interconnected by an elongated central section 26. In the preferred embodiment the bulbous shape of each end section is a sphere. However, it is contemplated that other shapes can be used as well, such as ovoids, cylinders, etc. Each end section is formed of a biocompatible material that it can be readily imaged and discerned by some type of imaging modality, e.g., X-ray imaging, ultrasound or magnetic resonance imaging. For example, as is known to those skilled in the art, for X-ray imaging it is the atomic weight/density/volume of the marker to be imaged that makes it visible and thus the material/volume of the bulbous end sections 26 of this invention are essential for visibility. In the exemplary preferred embodiment, where the imaging technology is X-ray, the spheres are formed of gold. However, other suitable materials can be used to form the spheres. Moreover, the spheres may be formed of one biocompatible material and coated with another biocompatible material providing that the resultant combination provides the desired atomic weight/density/volume for visibility by X-ray imaging. For ultrasonic imaging, the spheres may be formed of an echogenic material or coated with an echogenic material. Angiotech Pharmaceuticals, Inc. offers a suitable echogenic coating under the trademark ECHO-COAT®. For magnetic resonance imaging it is the electrical polarity/conductivity of the material and it's disturbance by RF signals that affects visibility, and volume rather than surface is essential here as well. Thus, in accordance with one preferred embodiment of this invention for magnetic resonance imaging, the spheres are formed of a non-conductive metal, e.g., titanium, or formed of any other suitable biocompatible material and coated with a non-conductive metal providing that the resultant combination provides the desire electrical polarity/conductivity and volume for visibility under magnetic resonance imaging.
As mentioned above, the spheres are connected together by an elongated central bridging section 26. In the preferred exemplary embodiment shown, the elongated bridging section is a rod-like member which is formed of a biocompatible material that is not readily imaged by the imaging modality used, so that the bridging section is considerably less discernable than the bulbous ends when the fiducial marker is imaged. For X-ray imaging applications the central bridging section 26 is preferably formed of a titanium or other biocomptible materials having a significantly lower density than gold so that it is is considerably less discernable, e.g., almost invisible, when imaged. For magnetic resonance imaging applications the elongated central section 26 may be formed of a biocompatible plastic. Accordingly, when the fiducial implant 20 is in position in the tissue to be localized, only the spheres 22 and 24 will be visible. This action effectively create a pair of points that can be used with the associated software, like the ISOLOC™ software, to help localize the marker. For most applications two fiducial markers will be implanted, thereby creating four discrete localizable points. The software may only need to utilize three of those points to localize the targeted tissue. In any case, in order to ensure precise localization of the targeted tissue it is of considerable importance that the distance between the two bulbous ends 22 and 24 of the fiducial marker 20 be fixed and maintained at that fixed, consistent distance from each other when the marker is implanted. Accordingly, the central section 26 of the fiducial marker is substantially rigid so that it doesn't flex or otherwise deform, which action could change the spacing between the bulbous ends of the marker. Moreover, the fixed distance between the spheres can be stored in the software for verification purposes.
In accordance with a preferred embodiment of this invention for use by X-ray imaging the ends 22 and 24 are formed of gold and each has a diameter in the range of approximately 0.5 mm to 3 mm, with the most preferred diameter being approximately 1.2 mm. The elongated rod-like central section 26 is formed of titanium and is of a diameter of approximately 0.2 mm to 2 mm, with the most preferred diameter being approximately 0.2 mm. The length of the rod-like member 26 is in the range of approximately 5 mm to 30 mm, with the most preferred length being approximately 10 mm.
As should be appreciated by those skilled in the art, the general overall “dumbbell” shape of the fiducial marker 20 tends to makes it quite resistant to migration. If further resistance to migration is desired, the surface of the marker may be textured. In particular, as shown in
The markers of this invention are arranged to be loaded into a needle or cannula 30, like shown schematically in
Without further elaboration the foregoing will so fully illustrate our invention that others may, by applying current or future knowledge, adopt the same for use under various conditions of service.
