Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
2002-01-11
2004-06-15
Jaworski, Francis J. (Department: 3737)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
C600S458000
Reexamination Certificate
active
06749554
ABSTRACT:
This invention relates to radiotherapy. More particularly, it relates to radioactive sources for use in brachytherapy, and in particular to radioactive sources with improved ultrasound imaging visibility.
Brachytherapy is a general term covering medical treatment which involves placement of a radioactive source near a diseased tissue and may involve the temporary or permanent implantation or insertion of a radioactive source into the body of a patient. The radioactive source is thereby located in proximity to the area of the body which is being treated. This has the advantage that the appropriate dose of radiation may be delivered to the treatment site with relatively low dosages of radiation to surrounding or intervening healthy tissue.
Brachytherapy has been proposed for use in the treatment of a variety of conditions, including arthritis and cancer, for example breast, brain, liver and ovarian cancer and especially prostate cancer in men (see for example J. C. Blasko et al.,
The Urological Clinics of North America
, 23, 633-650 (1996), and H. Ragde et al.,
Cancer
, 80, 442-453 (1997)). Prostate cancer is the most common form of malignancy in men in the USA, with more than 44,000 deaths in 1995 alone. Treatment may involve the temporary implantation of a radioactive source for a calculated period, followed by its removal.
Alternatively, the radioactive source may be permanently implanted in the patient and left to decay co an inert state over a predictable time. The use of temporary or permanent implantation depends on the isotope selected and the duration and intensity of treatment required.
Permanent implants for prostate treatment comprise radioisotopes with relatively short half lives and lower energies relative to temporary sources. Examples of permanently implantable sources include iodine-125 or palladium-103 as the radioisotope. The radioisotope is generally encapsulated in a titanium casing to form a sealed radioactive source or “seed” which is then implanted. Temporary implants for the treatment of prostate cancer may involve iridium-192 as the radioisotope.
Recently, brachytherapy has also been proposed for the treatment of restenosis (for reviews see R. Waksman,
Vascular Radiotherapy Monitor
, 1998, 1, 10-18, and
MedPro Month
, January 1998, pages 26-32). Restenosis is a renarrowing of the blood vessels after initial treatment of coronary artery disease.
Coronary artery disease is a condition resulting from the narrowing or blockage of the coronary arteries, known as stenosis, which can be due to many factors including the formation of atherosclerotic plaques within the arteries. Such blockages or narrowing may be treated by mechanical removal of the plaque or by insertion of stents to hold the artery open. One of the most common forms of treatment is percutaneous transluminal coronary angioplasty (PTCA)—also known as balloon angioplasty. At present, over half a million PTCA procedures are performed annually in the USA alone. In PTCA, a catheter having an inflatable balloon at its distal end is inserted into the coronary artery and positioned at the site of the blockage or narrowing. The balloon is then inflated which leads to flattening of the plaque against the artery wall and stretching of the artery wall, resulting in enlargement of the intraluminal passage way and hence increased blood flow.
PTCA has a high initial success rate but 30-50% of patients present themselves with stenotic recurrence of the disease, i.e. restenosis, within 6 months. One treatment for restenosis which has been proposed is the use of intraluminal radiation therapy. Various isotopes including iridium-192, strontium-90, yttrium-90, phosphorous-32, rhenium-186 and rhenium-188 have been proposed for use in treating restenosis.
Conventional radioactive sources for use in brachytherapy include so-called seeds, which are sealed containers, for example of titanium or stainless steel, containing a radioisotope within a sealed chamber but permitting radiation to exit through the container/chamber walls (U.S. Pat. No. 4,323,055 and U.S. Pat. No. 3,351,049 which are incorporated by reference). Such seeds are only suitable for use with radioisotopes which emit radiation which can penetrate the chamber/container walls. Therefore, such seeds are generally used with radioisotopes which emit &ggr;-radiation or low-energy X-rays, rather than with &bgr;-emitting radioisotopes.
In brachytherapy, it is vital to the therapeutic outcome for the medical personnel administering the treatment to know the relative position of the radioactive source in relation to the tissue to be treated, to ensure that the radiation is delivered to the correct tissue and that no localized over or under dosing occurs. Current seeds therefore typically incorporate a marker for X-ray imaging such as a radiopaque metal (e.g. silver, gold or lead). Location of the implanted seed is then achieved via X-ray imaging, which exposes the patient to an additional radiation dose. Such radiopaque markers are typically shaped so that imaging gives information on the orientation as well as location of the seed in the body, since both are necessary for accurate radiation dosimetry calculations.
Permanent implantation of brachytherapy radioactive sources for the treatment of, for example, prostate cancer may be done using an open laparotomy technique with direct visual observation of the radioactive sources and the tissue. However, the procedure is relatively invasive and often leads to undesirable side effects in the patient. An improved procedure comprising the insertion of radioactive sources transperineally into predetermined regions of the diseased prostate gland using an external template route to establish a reference point for implantation has been proposed (see for example Grimm, P. D., et al.,
Atlas of the Urological Clinics of North America
, Vol. 2, No. 2, 113-125 (1994)). Commonly, these radioactive sources, for example seeds, are inserted by means of a needle device while an external depth gauge is employed with the patient in the dorsal lithotomy position.
Preferably, the insertion or implantation of a radioactive source for brachytherapy is carried out using relatively non-invasive techniques such as, for example, techniques involving needles or catheters. It is possible to calculate a location for each radioactive source which will give the desired radiation dose profile. This can be done using knowledge of the radioisotope content of each source, the dimensions of the source, an accurate knowledge of the dimensions of the tissue or tissues in relation to which the source is to be placed, plus a knowledge of the position of said tissue relative to a reference point. The dimensions of tissues and organs within the body for use in such dosage calculations may be obtained prior to placement of the radioactive source by using conventional diagnostic imaging techniques including X-ray imaging, magnetic resonance imaging (MRI) and ultrasound imaging. Ultrasound imaging has the advantage of being a real time imaging technique.
However, difficulties may arise during the radioactive source placement procedure which may adversely affect the accuracy of the placement of the source if only pre-placement images are used to guide the source placement. For example, tissue volume may change as a result of swelling or draining of fluid to and from the tissue. Tissue position can change in the patient's body relative to a selected internal or external reference point as a result of for example manipulation during surgical procedures, movement of the patient or changes in the volume of adjacent tissue. Thus, it is difficult to achieve accurate placement of sources to achieve a desired dosage profile in brachytherapy using only knowledge of tissue anatomy and position that was obtained prior to the placement procedure. Therefore, it is advantageous if real-time visualisation of both the tissue and the radioactive source can be provided. A particularly preferred imaging method due to its safety, ease of use and low cost, is ultrasound i
Axellson Oskar
Coffey Steven
Gjorsvik Tore
Malmgren Hakan
Rydbeck Anna
Amersham PLC
Chisholm Robert F.
Jaworski Francis J.
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