Radiant energy – Calibration or standardization methods
Reexamination Certificate
1999-10-22
2002-03-26
Epps, Georgia (Department: 2878)
Radiant energy
Calibration or standardization methods
C600S436000
Reexamination Certificate
active
06362472
ABSTRACT:
The present application is related to U.S. patent application Ser. No. 09/266,961 filed on Mar. 12, 1999, which is hereby incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates, in general, to methods for processing signals from nuclear uptake probes for radiation detection and, more particularly, to methods of adjusting a control unit to calibrate a radiation detection system each time a new probe is used.
BACKGROUND OF THE INVENTION
Radioactive pharmaceuticals used in combination with radiation detection systems have been proven to be effective in locating radio labeled tissue within patients. These pharmaceuticals are also known as radionucleides and include solutions of Iodine 125, Iodine 131, and Phosphorous 32. Other radionucleides include monoclonal antibodies, peptides, and certain colloids labeled with radioactive isotopes such as Technetium-99. Once a radionucleide is introduced into a patient's body, it will tend to collect at targeted tissue sites, such as, for example, lymph node sites and such sites may be located by looking for concentrations of the radionucleide.
The mammalian lymphatic system has various interrelated functions, including circulating and modifying tissue fluid formed in capillary beds and removing cell debris and foreign matter. For certain cancers, neoplastic cells migrate and collect at regional nodes within an associated lymph drainage basin. Some cancers, such as those encountered in the breast, will evidence somewhat predictable nodal involvement. The axillary lymph node region is the principal site of regional metastasis from carcinoma of the breast, and approximately 40% of patients have evidence of spread to the axillary nodes. In some approaches to the disease, these axillary nodes are removed as a form of therapy.
Sentinel node biopsy is a less invasive alternative to lymph node dissection in diagnosing metastasis of breast cancer tumors. The principle of sentinel node biopsy is that neoplastic cells detaching from the primary tumor are most likely to be held by the sentinel node, which is the first lymph node to receive lymph from the involved area and the most likely site of early metastasis. If the sentinel node is free of cancer, it is highly probable that all of the other nodes are free of cancer cells. This knowledge helps the physician in staging the disease.
Thus, it is important to identify the sentinel node when trying to determine whether cancer has metastasized. Detection of a sentinel node may be achieved by using a gamma ray detection probe intra-operatively to assist surgeons in locating tissue tagged with a radionucleide. U.S. Pat. No. 5,732,704 to Thurston et al discloses a radiation based method for locating and differentiating sentinel nodes. The method described is used to identify a sentinel lymph node located within a grouping of regional nodes at a lymph drainage basin connected to neoplastic tissue. A radionucleide is injected near the neoplastic tissue and migrates along a lymph duct toward the drainage basin containing the sentinel node. A hand-held, radiation detection probe is moved along the lymph duct while the operator observes a graphical readout of count rate amplitudes to determine when the probe is aligned with the duct. The region containing the sentinel node is identified when the count rate at the probe substantially increases. Following incision, the probe is maneuvered using a sound output to establish increasing count rate thresholds. The probe is then moved incrementally until the probe is adjacent to the sentinel node, which then may be surgically removed. The visual and audio signals used by the surgeon are generated by the signal processing portion of the radiation detection system, which may be referred to as the control unit control unit. The control unit is connected to the handheld probe to form the radiation detector system.
The success of using a method such as disclosed in U.S. Pat. No. 5,732,704 depends upon the reliability of the hand-held radiation detection probe and the calibration between the probe and the control unit. The probe generally operates at room temperature and is designed to detect very low levels of gamma radiation. The gamma radiation emitted from the sentinel node may be masked by background noise such as cosmic radiation, thermal noise, and capacitively or piezoelectrically induced noise resulting from manipulation of the probe itself. One function of the control unit is to filter gamma radiation emitted by the radio tagged tissue from background noise and other sources of gamma radiation, including Compton scatter.
Gamma ray detection probes may include a high-Z semiconductor (such as CdZnTe or CdTe) or a scintillation crystal such as sodium-iodide (NaI) which is coupled with a small photo multiplier tube. U.S. patent application Ser. No. 09/066,545, filed on Apr. 24, 1998, now abandoned, describes a relatively low-cost radiation detection probe. The probe integrates a silicon photodiode detector (with or without a scintillation assembly) with amplifiers, interface electronics, and radiation shielding, into one compact radiation probe assembly. The probe assembly uses relatively low voltages, has relatively few electrical connections, is relatively easy to manufacture, and is low-cost. The disclosed radiation detection probe is particularly useful for detecting radionucleides during lymphatic mapping and localization of a sentinel node.
Despite recent advances to lower the cost of manufacture and use of radiation detection probes, it is still necessary to insure that the electronic signal generated by the probes are correctly interpreted by the control unit. Careful attention to manufacturing tolerances and the use of specially selected electronic components may ensure adequate calibration between probes and adequate stability after the probes leave the factory, thus ensuring that the output for a given input is relatively constant across a selection of probes and relatively stable over time. Of course, such manufacturing tolerances and special electronics add significant cost. Lower cost probes, on the other hand, may be manufactured to wider tolerances and utilize less expensive electronics, making them less consistent probe to probe and more likely to lose calibration after leaving the factory. One particularly important characteristic of radiation detection probes is the signal output level generated by a predetermined signal input level. For example, one probe may generate an electronic pulse output of 5.1 volts when a gamma ray having an energy level of 140.5 kilo electron Volts (keV) is detected. An energy level of 140.5 keV is typical of a gamma ray photon generated by Technetium-99. However, because of a number of factors, including manufacturing tolerances and variations in electronic component characteristics, an identically manufactured probe may generate an electronic pulse of 4.9 volts when detecting a gamma ray photon having an energy level of 140.5 keV. Further, even if the output of a particular probe is within acceptable tolerances at the factory, the output signal level may shift over time. When using probes which vary over time or from probe to probe, the control units must, therefore, be calibrated using a known radioactive source so that the electronic output signals from the probe are correctly interpreted by the radiation detection system.
Radiation detection systems are typically calibrated against a radioisotope which has a known peak energy level. This may be accomplished by, for example, calibrating each radiation detection system periodically in a biomedical lab. The probe is held near a radioisotope having a known, characteristic, gamma radiation energy level. Each gamma ray photon emitted by the radioisotope represents a singular radioactive event and each gamma ray photon has an energy level measurable in kilo electron volts (keV). Each such gamma ray photon or radioactive event which is detected by a probe may be referred to as a count. Upon detecting gamma ray photons, the probe generates a
Gormley Jerome E.
Yarnall Stephen T.
Epps Georgia
Ethicon Endo-Surgery Inc.
Hanig Richard
LandOfFree
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