Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
2000-08-17
2003-04-22
Hindenburg, Max F. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
Reexamination Certificate
active
06551232
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to devices and methods for utilization in brachytherapy in the fields of medical physics and therapeutic radiology. More specifically, the present invention relates to brachytherapy dosimetric protocols utilizing the neutron-emitting radioisotope californium-252 (
252
Cf), as well as
252
Cf encapsulation, storage, and remote delivery (afterloading) methodologies.
BACKGROUND OF THE INVENTION
I. Brachytherapy
Radiation therapy refers to the treatment of diseases with ionizing radiation. Of particular interest is the treatment of neoplastic disease, especially solid, malignant tumors. In radiation therapy, to goal is to destroy the malignant tissue while concomitantly minimizing the exposure of medical personnel to radiation and minimizing radiation damage to other tissue, such as nearby healthy tissue. The recognized method employed for radiation treatment in body cavities (e.g., the throat, bowel or vaginal region, and in regions of the body opened surgically) is brachytherapy, in which one or more radiation sources is brought, controlled by an afterloading device, in a precise and metered manner to the site of treatment in the body. The radiation source is then moved to provide a previously-calculated isodose contour. See, e.g., See, Nath, et al., 1995. Dosimetry of interstitial brachytherapy sources: Recommendations of the AAPM Radiation Therapy Committee Task Group No. 43
, Med. Phys
. 22: 209-234); Lukas, et al., Intraoperative Radiotherapy with High Dose Afterloading (Flabs Method), in:
Intraoperative Radiation Therapy” Proceedings
4th
International Symposium IORT
, Schildberg and Kramling, eds., 1992 (Verlag Die Blaue Eule, Essen).
In brachytherapy, there is a relatively short distance (i.e., typically 0.1-5 cm) between the radioactive source and the tissue which is to receive radiotherapy. It should be noted however that brachytherapy is a comprehensive term, and includes radiotherapy effected by interstitial, intercavitary, and surface application (plaque). Interstitial and intracavitary techniques are particularly advantageous where deep-seated lesions are involved while plaque therapy is particularly advantageous where superficial or accessible diseased tissue is involved. In contrast, another form of radiation therapy, “external beam therapy”, involves treatment at relatively large distances (i.e., 50-500 cm) between the radiation source and the skin surface. Accordingly, with “external beam therapy,” it generally is difficult to mitigate damage to underlying disease yet spare the normal tissues which may be included in the path of the radiation towards the target. Recent approaches using intensity-modulated radiotherapy (See, e.g. Tsai, et al., 2000. Dependence of linac output on the switch rate of an intensity-modulated tomotherapy collimator,
Med. Phys
. 27).
There are two general types of brachytherapy, those involving permanent implants and those which utilize temporary implants. Although a wide variety of radioactive elements (“radioisotopes”) have been previously proposed for therapeutic use, only a relatively small number have actually been accepted and employed on a large-scale basis. This is due, at least in-part, to a relatively large number of constraining considerations where medical treatment is involved (i.e., the energy of the emitted radioactivity, half-life, availability, and the like). An element employed almost immediately after its discovery in 1898, was radium. Although radium possesses a long half-life (i.e., approximately 1600 years), a particularly undesirable property is the requirement for careful attention to the protection of medical personnel, as well as healthy tissue of the patient. This is due to its complex and highly penetrating gamma ray emission. To minimize exposure to medical personnel, specialized and sometimes complicated “after loading” techniques have been developed whereby the radioisotope is guided, for example through a hollow tube, to the treatment region following preliminary placement of the specialized appliances required.
More recently, permanent implants using radioactive “seeds” containing iodine-125 have been previously employed. Similarly, for temporary implants, cesium-137, iridium-192, and palladium-103 sources have been employed. These radionuclides will be briefly discussed, infra. In addition, the use of xenon-133 and xenon-131 have also be suggested.
In order to avoid harming the patient and to guarantee the requirements for accurate irradiation, the radioactive source(s) must be accurately positioned and fixed on or in the body. Only when this is ensured can programming of the required isodose contour take place and properly pre-planned irradiation be guaranteed. If the radiation source is not accurately positioned, there may be considerable overdosage to normal (i.e., non-tumorogenic) tissue, with serious risk of harm to the patient, or exposure of medical staff to radiation. See, e.g., Gosh, 1991. Sicherheitstechnisch bedeutsame Ereignisse an Afterloadinganlagen: Untersuchungen zur Strahlenexposition, Folgerungen zur Sicherheit von Personal und Patient [Events with relevance to safety in afterloading systems: Investigations on radiation exposure, consequences for safety of staff and patient]
Diplomarbeit Berufsakademie, Karlsruhe
. Additionally, in cases of repeated radiation treatments, where a reduced radiation dose is given in each subsequent treatment, accurate localization of the radioactive source(s) at the site of treatment over a lengthy period is of particular importance.
II. Radionuclides Traditionally Utilized in Brachytherapy
Initially, interstitial implants were performed with radium-226 (
226
Ra) needles. However, due to serious radiation safety considerations from the highly penetrating gamma-rays, this radioisotope has largely been replaced with other radionuclides. Currently, the vast majority of interstitial brachytherapy treatments in North America are done using either iridium-192 (
192
Ir), iodine-125 (
125
I), or cesium-137 (
137
Cs) sources. Recently, palladium-103 (
103
Pd) sources have also become available for permanent implants. A brief description of
92
Ir,
125
I,
137
Cs, and
103
Pd sources is given in the following sections.
1. Iridium-192 (
92
Ir) Sources
192
Ir is produced when stable
191
Ir (37% abundance) absorbs a neutron.
192
Ir decays with a short 73.83 day half-life to several excited states of
192
Pt and
192
Os which are both gamma ray emitters with a varying range of energies. The average energy of the emitted photons from an unencapsulated source is approximately 0.4 MeV. In the United States,
192
Ir is used for interstitial radiotherapy is usually in the form of small cylindrical sources or “seeds” which are from 3 to 10 mm long and approximately 0.5 mm in diameter.
2. Iodine-125 (
125
I) Sources
125
I is produced when
124
Xe absorbs a neutron, and then decays via electron capture.
125
I itself decays with a half-life of only 59.4 days, by electron capture to the first excited state of
125
Te, which subsequently undergoes internal conversion 93% of the time and otherwise emits a 35.5 keV gamma-ray. The electron capture and internal conversion processes give rise to characteristic x-rays.
125
I for interstitial implants is available commercially in the form of small “seeds” of varying sizes and activities.
3. Palladium-103 (
103
Pd) Sources
103
Pd is formed when stable
102
Pd absorbs a neutron. It decays via electron capture, mostly to the first and second excited states of
103
Rh with a 17.0 day half-life. De-excitation is almost totally via internal conversion, leading to the production of characteristic x rays. Average photon energy is approximately 21 keV.
103
Pd sources are similar in size and encapsulation to those for
125
I sources, typically being 4.5 mm long and 0.8 mm in diameter.
4. Cesium-137 (
137
Cs) Sources
137
Cs possesses a half-life of 30 years. Gamma radiation from
137
Cs has an energy of 662 keV, which in comparison to the other radionuclides in this section,
Beattie Ingrid A.
Cadugan Joseph A.
Hindenburg Max F.
Hunter Shane H.
Mintz Levin Cohn Ferris Glovsky and Popeo PC
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