Coiled brachytherapy device

Details Coiled brachytherapy device Coiled brachytherapy device

1999-05-21

2002-07-16

Gilbert, Samuel G. (Department: 3736)

Surgery

Radioactive substance applied to body for therapy

Radioactive substance placed within body

Reexamination Certificate

active

06419621

ABSTRACT:

TECHNICAL FIELD
The invention is directed to implantable brachytherapy devices.
BACKGROUND OF THE INVENTION
It is known to treat proliferative tissue, such as tumors, lesions and stenoses of biological passageways, with radiation in order to inhibit or prevent cellular proliferation by preventing replication and migration of cells and by inducing programmed cell death. Traditional high-dose external beam radiation treatment, and prolonged low dose rate, close-distance radiation treatment (brachytherapy), are well-established therapies for the treatment of cancer, a malignant form of cellular proliferation.
It is important in the administration of radiation that it be properly targeted so as to be effective against undesirable cellular proliferation without adversely affecting normal cellular responses. Externally applied radiation requires careful control over the depth and breadth of radiation penetration so as not to damage healthy tissue surrounding the lesion to be treated. Close-distance radiation treatment also requires careful control over the penetration and directionality of the radiation, but this can be done over substantially smaller distances.
The radioactivity may be incorporated into or onto an implantable device. Such implantable devices are typically quite expensive to manufacture. In particular, if radioactivity is added to the device, the device may only be effective for brachytherapy during a relatively short period during which the radioactivity is provided at a useful (therapeutic) level. Depending on the radioisotope used, the decay time may be as short as hours, days or weeks.
The current state of the art brachytherapy for treatment of localized lesions such as tumors of, for example, the prostate, breast, brain, eye, liver, or spleen, employs radioactive, sealed source seeds. The term “sealed source”, as used herein, means that radioisotopes incorporated into a device are integral with the device and cannot be dislodged or released from the host material of the device in the environment of usage. A typical sealed source seed includes a radiation source encapsulated within an impermeable, biocompatible capsule made of, for example, titanium, which is designed to prevent any leaching or release of the radioisotope. The seeds are approximately the size of a grain of rice (typically 0.81 mm in diameter by 4.5 mm long) and are implanted individually at a treatment site within and/or around a lesion, typically with a medium bore (18-gauge) delivery needle.
Disadvantages of the use of such seeds as brachytherapy devices include their nature as discrete, or point, sources of radiation, and the corresponding discrete nature of the dosages which they provide. In order to provide an effective radiation dose over an elongated or wide target area, the seeds should be uniformly and relatively closely spaced. The need to ensure accurate and precise placement of numerous individual radiation sources undesirably prolongs the surgical procedure, and hence the exposure of the surgical team to radiation. Moreover, the use of discrete seeds requires an elaborate grid matrix for their proper placement. This requirement is labor-intensive, and therefore costly. In addition, the discrete nature of the seeds renders them more susceptible to migration from their intended locations, thereby subjecting portions of the lesion, the treatment site, and surrounding healthy tissue to over- or under-dosage, reducing the effectiveness and reliability of the therapy.
Other disadvantages exist in radioactive seed therapy. Relatively few radionuclides are suitable for use in sealed-source seeds, because of limited availability of radioisotopes with the necessary combination of half-life, specific activity, penetration depth and activity, and geometry. In addition, the implantation of seeds generally requires a delivery needle with a sufficiently large bore to accommodate the seeds and may, in some cases, require an additional tubular delivery device. The use of a relatively large delivery needle during seeding may cause unnecessary trauma to the patient and displacement of the lesion during the procedure. Also, because of the risk of migration or dislodgement of the seeds, there is the risk that healthy tissues near or remote from the lesion site will be exposed to radiation from seeds which have become dislodged from their intended locations and possibly carried from the body within urine or other fluids.
Various radioisotopes have been proposed for brachytherapy. Brachytherapy devices made of palladium-103 are desirable because palladium-103 has a half life of about 17 days and a photon energy of 20.1-23 KeV, which makes it particularly suitable for use in the treatment of localized lesions of the breast, prostate, liver, spleen, lung and other organs and tissues.
Because palladium-103 is unstable and not naturally occurring in the environment, it must be manufactured, generally either by neutron activation of a palladium-102 target, or by proton activation of a rhodium target. These processes are disclosed in, for example, U.S. Pat. No. 4,702,228 to Russell, Jr. et al. (neutron activation) and U.S. Pat. No. 5,405,309 to Carden, Jr. (proton activation).
Brachytherapy devices employing radioisotope coatings are also known. U.S. Pat. No. 5,342,283 to Good discloses the formation of concentric radioactive and other discrete coatings on a substrate by various deposition processes, including ion plating and sputter deposition processes, as well as via exposure of an isotope precursor, such as palladium-102, to neutron flux in a nuclear reactor.
A disadvantage of the radioactive devices made by any of the above processes is that they cannot be made economically or simply. The processes are either prohibitively expensive and require lengthy and costly wet chemistry separation steps to isolate the radioactive isotope from the non-radioactive precursor, or they are relatively complicated, multistep processes which are difficult to control and which may produce coatings that can deteriorate with time and/or exposure to bodily fluids, resulting in dissemination of radioactive and other materials into the body, with potentially harmful consequences.
A highly versatile form of a device for interstitial radiation treatment is a wire or rod which can be inserted into the tissue at a lesion site and then bent or shaped as needed to encircle or otherwise assume a useful shape for administration of radiation to the lesion and/or to surrounding tissue. Greater versatility, flexibility and specificity of treatment can be provided as the size (diameter) of the wire decreases; however, such fine wires are also generally difficult to see, handle and maneuver, and this limits their utility in many treatment applications.
U.S. Pat. No. 5,498,227 to Mawad discloses a shielded implantable radioactive wire which includes a radioactive inner core and a buffer or shielding layer in the form of a flexible metal wire or ribbon wrapped around the core. The purpose of the buffer layer is to attenuate radiation emitted from the inner core. The wire can be formed into a helical coil shape and can be made of a shape-memory material which allows the device to be inserted into a treatment site in a straightened configuration and then relaxed to its original helical shape. The device has particular application as an expandable helical coil stent to deliver therapeutic radiation to, and maintain the patency of, occluded biological passageways. The diameter of the inner core, as well as of the wire used as the buffer layer, is in the range of about ten to fifty thousandths of an inch (0.010″-0.050″), or about 0.25 to 1.25 millimeter, and the diameter of the helical coil formed from the wire is in the range of about 1 millimeter to 2 centimeters.
U.S. Pat. Nos. 5,176,617 and 5,722,984 to Fischell et al. also disclose radioactive helical coil stents for use in maintaining the patency of biological passageways. Such stents generally have an undeployed diameter in the range of about 1.5 to 2 millimeters, and a deployed

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