Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-08-14
2001-10-02
Casler, Brian L. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S428000, C600S437000, C378S062000, C378S065000
Reexamination Certificate
active
06298260
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to apparatus and methods for use in therapeutic treatment and in diagnosis of medical patients. More specifically the invention relates to apparatus and methods which provide incident therapeutic or diagnostic energy to a medical patient during a selected portion of the patient's respiratory cycle, thereby diminishing inaccuracies in the assumed spatial location of the portion of the patient being treated or diagnosed which arise from the patient's respiration. The invention is applicable to diagnostic or therapeutic treatment with electromagnetic, sonic or other incident energy, including therapeutic treatment and diagnostic procedures based on x-rays, gamma rays, or visible or near visible radiation; energy fields which are incident to MRI; and/or energy rendered incident on the patient by detectable charged or uncharged particle beams.
BACKGROUND OF INVENTION
Although the invention is broadly applicable as above indicated, the problem to which it is addressed is especially well illustrated by considering the field of radiation therapy. A principal goal of such therapy is to deliver a radiation dose appropriate to achieve the purpose of treatment (e.(g. tumor eradication, palliation), while simultaneously minimizing dosage to surrounding normal (healthy) tissues, reducing the likelihood of clinically significant damage to these tissues. These objectives may be appreciated by referring to the schematic depiction of
FIG. 1
, which illustrates the ICRU definitions for appropriate target volumes for a patient undergoing radiation therapy. (See landberg, T. Chavaudra, J.; Dobbs, J.; Hanks, G.; Johansson, K.; Moller, I.; Purdy, J.; “Prescribing, Recording, and Reporting Photon Beam Therapy”. International Commission on Radiation Units and Measurements, 50, 1993. The Gross Tumor Volume (GTV) is the gross palpable or visible/demonstrable extent and location of malignant growth. The Clinical Target Volume (CTV) is a tissue volume that contains a demonstrable GTV and/or subclinical microscopic malignant disease, which has to be eliminated. This volume thus has to be treated adequately in order to achieve the aim of therapy, cure or palliation. The Planning Target Volume (PTV) is a geometrical concept, and it is defined to select appropriate beam sizes and beam arrangements, taking into consideration the net effect of all the possible geometric variations, in order to ensure that the prescribed dose is actually absorbed in the CTV. The Treated Volume is the volume enclosed by an isodose surface, selected and specified by the radiation oncologist as being appropriate to achieve the purpose of treatment (e.g. tumor eradication, palliation). The gross target volume (GTV) and clinical target volume (CTV) thus contain tissues to be treated, while the planning target volume (PrV) places a margin around the CTV to account for patient movement and uncertainties in treatment set up.
In the last several years, conformal therapy techniques are being used with increasing frequency. These techniques combine good patient immobilization to minimize the PTV margin around the CTV coupled with the use of multiple, non coplanar beams to reduce treated volume margin beyond the PTV. The ultimate goal of conformal therapy is to deliver a treatment in which the CTV, PTV and treated volumes are identical. The use of intensity modulated radiotherapy (IMRT) and multiple, non coplanar beams has substantially improved the conformation of the treated volume to the PTV.
In the thorax and abdomen, the PTV margin beyond the CTV remains relatively large. A large contributory factor is the organ motion due to respiration. Motion of the heart, kidney, liver, pancreas, and spleen may be several centimeters, requiring a large PTV. In diagnostic imaging, organ motion has been recognized as a significant cause of image blurring. Several techniques may be used to reduce respiratory organ motion. Retrospective or prospective image correction techniques such as navigator echo imaging work well for MRI, but are not applicable to radiation therapy. Breath holding has been used with success for spiral CT scanner image acquisition but is not practical for radiation therapy, because the beam on time is typically too long for most patients to hold their breath. In lithotripsy, respiratory induced kidney motion inhibits accurate localization.
In radiation therapy, the potential reduction in the PTV margin, accomplished by minimizing the effects of organ motion due to respiration, may be as great as the reduction in the treated volume margin gained by using conformal therapy techniques. Yet, methods to reduce organ motion in radiation therapy have been limited and typically have employed impedance plethysmography or pneumotachometry, measuring changes in chest or abdomen position or pressure, usually by means of a sensor such as a belt attached to the patient. These devices may have calibration problems caused by variation of the tightness of the belt between treatments or slippage that occurs during treatment. If the device is in the beam, radiation damage to the device or loss of skin sparing may occur. In radiation therapy, the challenge is not simply to freeze respiratory motion for a single session, as is the case in diagnostic imaging, but to do so reproducing the diaphragm position between consecutive respiratory cycles, radiation beams and treatment days. The procedure employed must ensure reproducibility of organ position not only during treatment but for diagnostic image acquisition used in treatment planning as well.
SUMMARY OF INVENTION
Now in accordance with one aspect of the present invention, a method is provided for gating therapeutic or diagnostic energy to a tissue volume of a medical patient during a selected portion of the patient's respiratory cycle, to thereby diminish inaccuracies in the assumed spatial position of the tissue volume arising from displacements induced by the patient's respiration. Pursuant to the method the gases flowing to and from the patient's lungs are monitored to provide quasi-continuous measurements as a function of time, of at least two of (a) flow rate, (b) pressure, (c) patient lung volume and (d) carbon dioxide concentration. Preferably measurements of all four of these parameters are provided. These measurements are used to trigger the time period during which the said energy is gated at the beginning of the selected portion of the respiration cycle; and optionally to terminate the time period during which the said energy is gated, at the end of the selected portion of the respiration cycle. Alternatively the energy gating period can be terminated independently of measurements (a) through (d).
The selected portion of the respiration cycle may start at substantially full exhalation and can include a respiration hold introduced in the cycle by the patient at substantially full exhalation. In such circumstances and assuming that all four of the mentioned parameters are measured, the energy is gated on when at the same time (1) the gas flow rate and pressure are below predetermined thresholds; (2) the lung volume is below a predetermined threshold; and (3) the carbon dioxide level is above a predetermined threshold. The predetermined thresholds for the four individual channels are set as follows: The pressure threshold is set as a user defined fraction of the previous pressure peak value (the last maximum before the signal crosses zero). When the pressure falls below the calculated level, the gate for that particular signal is opened (“ON”). When the pressure rises above the calculated level, the gate for that particular signal is closed (“OFF”). Flow is handled identically. The threshold for CO
2
is chosen graphically utilizing the display of a computer forming part of the system that will he further described below. In training mode, a trace of the CO
2
is represented on the computer screen and a moving bar is dragged up and down indicating the desired predetermined level for CO
2
to gate on. When CO
2
ex
Burnham Bentley H.
Sontag Marc R.
Casler Brian L.
Klauber & Jackson
St. Jude Children's Research Hospital
LandOfFree
Respiration responsive gating means and apparatus and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Respiration responsive gating means and apparatus and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Respiration responsive gating means and apparatus and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2577132