Apparatus for treating a target site of a body

Apparatus for performing a procedure at a target site of a patient's body, the apparatus comprising: a continuous positive airway pressure (CPAP) apparatus that provides CPAP to the patient's lungs; a medical device for performing the procedure at the target site; and a controller that controls the CPAP apparatus to provide CPAP to the patient's lungs during performance of the procedure.

TECHNICAL FIELD

Embodiments of the invention relate to treating a target site in a patient.

BACKGROUND

Various methods of treating patients with different types of radiation have matured since E. O. Lawrence first used neutron radiation to cure his mother of cancer in 1932, and R. R. Wilson first suggested using protons to treat cancer in a seminal paper in 1946. Today, most medical centers have, or have access to, at least one facility for generating a radiation beam for treating malignancies. The facility generally comprises an accelerator for accelerating a beam of charged particles, for example electrons or protons, a target with which the beam collides to produce a desired type of radiation, and apparatus for accurately aiming the desired radiation as a well defined therapeutic radiation beam at a target site of a malignancy in a patient's body. The radiation beam may be a particle beam of electrons, a beam of hadrons, such as protons, neutrons, or alpha particles, or a beam of electromagnetic radiation, such as X-rays or gamma rays.

Therapeutic radiation beams operate to kill malignant cells at a target site of a malignancy by depositing an amount of radiant energy at the target site sufficient to damage the DNA of the malignant cells. Malignant cells at the target site suffering sufficient damage to their DNA die and are removed from the body by natural processes. However, radiation in a therapeutic radiation beam does not distinguish between healthy cells and malignant cells, and may damage healthy cells as well as malignant cells. As a result, therapeutic radiation beams generally have to be accurately configured and aimed at a target site of a malignancy to concentrate deposited radiant energy at the malignancy, and minimize deposition of radiant energy to surrounding healthy tissue.

For malignancies, such as malignancies in or on the appendages, or the brain, which may relatively easily be stabilized and kept stationary during radiation therapy, therapeutic radiation beams may generally effectively be configured to localize deposition of radiant energy to the malignancies. For malignancies located in or on an organ of the thoracic or abdominal regions of the body, such as malignancies of the left breast, lungs, liver, and pancreas, breathing may generate relatively large motion of the organ and thereby the malignancies. Maintaining a radiation beam focused on the moving malignancies may be a relatively complex and difficult undertaking.

A conventional procedure for depositing radiant energy by a therapeutic radiation beam to a malignancy exhibiting motion during irradiation may involve forming the beam sufficiently large so that the malignancy remains within the beam cross section throughout irradiation. To moderate exposure of healthy tissue during irradiation, a therapeutic radiation beam may be controlled to follow motion of the malignancy during irradiation. Alternatively or additionally, a therapeutic radiation beam may be shuttered on and off in synchrony with a patient's respiratory motion so that doses of radiation are delivered to the malignancy each time it moves through a same given location. In some procedures, attempts may be made to physically constrain a patient's respiratory motion during irradiation by pressing on the patient's abdomen to moderate motion of the malignancy due to respiration during irradiation.

SUMMARY

An aspect of an embodiment of the invention relates to providing apparatus, hereinafter also referred to as “Steady-Site”, for performing a procedure at a target site in the thoracic or abdominal regions of a patient's body and constraining movement of the target site due to respiratory motion during the procedure. Steady-Site may comprise at least one or any combination of more than one of a diagnostic, interventional, and/or therapeutic device, to be delivered to the target site for performance of the procedure or for delivering an agent to the target site for performance of the procedure. Hereinafter a diagnostic, interventional, and/or therapeutic device in accordance with an embodiment of the invention may be generically referred to as a medical device. An agent may comprise a substance and/or energy for delivery to the target site. Steady-Site comprises apparatus for providing continuous positive airway pressure (CPAP) to the patient's lungs during the procedure to constrain motion of the target site, expand the chest cavity and lungs, and/or displace organs and tissue in the chest cavity to distance them from the target site.

A procedure performed at a target site, or treating a target site, may refer to any medical or imaging procedure that may be performed at, in, or of the site, or any combination of more than one of such procedures. In an embodiment of the invention the medical device may be a manually operated or deployed medical device or a robotic device that operates autonomously or semi-autonomously to deliver an agent to the target site and/or to deploy at the target site.

In an embodiment of the invention, Steady-Site may comprise a controller that controls delivery of the medical device and/or agent. Optionally, the controller controls the CPAP apparatus to provide CPAP during performance of the procedure. The CPAP provided during the procedure in accordance with an embodiment of the invention operates to flatten and reduce motion of the diaphragm during respiration, and expand the lungs and chest cavity. The CPAP thereby moderates motion of tissue and organs in the thoracic and abdominal regions due to patient respiration, and as a result, motion of the target site during irradiation. Expansion of the lungs and chest cavity tends to reposition and increase spacing between organs in the chest cavity and abdomen. The reduced motion of the target site and other organs and tissue in the thoracic and abdominal regions of the patient facilitates delivery of a medical device or agent to the target site and contributes to reduction of possible collateral damage to tissue outside of the target site resulting from delivery of the medical device or agent. Expansion of the lungs and chest cavity and resultant repositioning and spacing of organs in the chest and abdomen may also facilitate delivery of a medical device or agent to the target site and reduction of possible collateral damage to tissue outside of the target site resulting from delivery of the medical device or agent.

For example, CPAP administered in accordance with an embodiment of the invention, tends to displace the heart caudally relative to the left breast. As a result, the heart may benefit from reduced exposure to radiation in a radiation beam directed to deliver a dose of radiation to a target site comprising a malignant lesion of the left breast. Expansion of the lungs due to CPAP reduces density of lung tissue, which generally improves contrast between tissue in the target site and lung tissue for medical imaging modalities that might be used to acquire images of a target site in the thoracic region of a patient.

In an embodiment of the invention, a Steady-Site apparatus, which may be referred to as Steady-Site ACCURAD, or ACCURAD, is configured to provide radiation therapy and comprises radiation therapy equipment for delivering radiation to a target site of, optionally a malignancy, in the thoracic or abdominal regions of a patient's body with reduced exposure of healthy tissue in a neighborhood of the malignancy to the radiation. Steady-Site ACCURAD optionally comprises a radiation beam and a controller that controls the radiation beam, and the CPAP apparatus to provide CPAP during irradiation of the target site by the radiation beam. An ACCURAD therapeutic radiation beam may therefore generally be relatively accurately aimed at the malignancy and be configured having a smaller cross section perpendicular to its direction of propagation than therapeutic radiation beams provided by conventional radiation facilities. The ACCURAD therapeutic radiation beam is therefore generally able to deliver radiation to a target site of a malignancy with reduced collateral damage to healthy tissue

An aspect of an embodiment of the invention relates to determining an internal target volume (ITV) for a malignancy of a patient to be irradiated by an ACCURAD radiation beam. An ITV for a malignancy is generally defined to include a clinical target volume (CTV) of the malignancy, which is a volume of tissue that contains a gross tumor volume (GTV) that characterizes the malignancy, as well as tissue peripheral to the GTV that is considered to require radiation therapy. The ITV is generally larger than the CTV and is defined as a volume that substantially contains, and within which the CTV may be predicted to move as a result of motion, generated for example by the patient's respiratory motion, of the malignancy during irradiation. In accordance with an embodiment of the invention, motion of the patient's malignancy is imaged, optionally using an MRI (magnetic resonance imaging) scanner and/or a CT (computed tomography) scanner, which may for example perform a 4D (four dimension) CT scan, PET/CT (positron emission tomography/CT)scan, or cone beam CT scan during provision of CPAP to the patient. The reduced motion of the malignancy, increased separation of organs, and improved tissue contrast resulting from the provision of CPAP enables determination of an ITV, hereinafter also referred to as a CPAP-ITV, for treating the malignancy with the ACCURAD radiation beam that is generally smaller than a conventional ITV.

In an embodiment of the invention ACCURAD may comprise a medical imager such as by way of example, an ultrasound, PET, MRI, or a CT scanner, and the ACCURAD controller controls the CPAP apparatus and the medical imager to acquire images of the malignancy and motion of the malignancy during provision of CPAP to determine the CPAP-ITV. Optionally, the controller comprises a computer executable instruction set for image processing the images to determine a GTV and CTV for the malignancy and/or for determining the CPAP-ITV.

In the discussion, unless otherwise stated, adjectives such as “substantially” and “about” modifying a condition or relationship characteristic of a feature or features of an embodiment of the invention, are understood to mean that the condition or characteristic is defined to within tolerances that are acceptable for operation of the embodiment for an application for which it is intended. Unless otherwise indicated, the word “or” in the description and claims is considered to be the inclusive “or” rather than the exclusive or, and indicates at least one of, or any combination of items it conjoins

DETAILED DESCRIPTION

The following detailed description describes a conventional procedure, schematically illustrated inFIGS. 1A-1Cfor, by way of example, irradiating a malignant lesion of the left lower lung of a patient to deliver a therapeutically effective dose of radiation to the lesion. The illustrated conventional procedure shows movement of the lesion during irradiation due to respiratory motion of the lungs and diaphragm and resultant exposure of healthy tissue to radiation.FIG. 2schematically shows a similar procedure performed on the same lesion by a Steady-Site ACCURAD apparatus in which motion of the lesion is moderated by CPAP, and a relatively narrow focused beam of radiation irradiates the lesion in accordance with an embodiment of the invention. The moderated motion of the lesion and narrow beam of radiation reduces exposure of healthy tissue surrounding the lesion to radiation. A flow diagram for a procedure for treating a target site, optionally malignant lesion, in accordance with an embodiment of the invention is shown inFIG. 3and discussed with reference to the figure.

FIGS. 1A-1Cschematically show a patient100being treated for a malignant lesion represented by a solid circle60by a conventional radiology machine120. The size of solid circle60schematically represents a clinical target volume (CTV) determined for the lesion. In the figures, outer boundaries of left upper lobe (LUL)102and left lower lobe (LLL)104of the left lung in the patient's chest cavity106, are indicted by fine dashed lines, and the patient's diaphragm110is shown in a bold dashed line. Lung tissue within the fine dashed lines outlining LUL102and LLL104is indicated by dotted shading. Density of lung tissue is schematically represented by density of the shading. By way of example, malignant lesion60is located on LLL104.

Radiology machine120comprises a radiation beam generator122and a controller124that controls beam generator122to irradiate patient100with a radiation beam130having characteristics that are advantageous for delivering a desired dose of radiation to lesion60that may control and eradicate the lesion. The figures show radiology machine120irradiating patient100during a respiratory cycle. Optionally, radiation beam130is a beam of X-rays.

Lesion60undergoes substantial motion during respiration of patient100, and radiation beam130is configured by controller124having a solid angle sufficiently large so that the lesion does not move outside of the beam at any time during the patient's respiratory cycle. In particular, a component of motion of lesion60during respiration of patient100parallel to the sagittal plane (not shown) of the patient's body is relatively large. The plane ofFIGS. 1A-1Cis parallel to the patient's sagittal plan and is assumed to intersect the trajectory of motion that lesion60executes during respiration. Therefore, to contain lesion60during respiration, controller124controls beam generator122to configure radiation beam130so that the radiation beam has a relatively large cross section defined by a relatively large opening angle θ in the plane ofFIGS. 1A-1C.

InFIG. 1A, patient100has just completed exhaling, the patient's diaphragm110is maximally elevated into the chest cavity, to contract the chest cavity volume and compress lung volume substantially to their minimum, and patient100is about to initiate inhalation. As a result of the compressed lung volume, lung tissue density is substantially at a maximum, which is schematically indicated by relatively dense shading of LUL102and LLL104. Lesion60is located high in the chest cavity near a lower right edge107of radiation beam130.

InFIG. 1Bpatient100is inhaling and substantially in the middle of the inhalation portion of the patient's respiratory cycle. Diaphragm110is partially contracted to move the diaphragm inferiorly away from the chest cavity to expand and reduce pressure in the chest cavity and expand and draw air into the lungs. As a result of motion of diaphragm110, associated expansion of chest cavity106and rib cage (not shown), and expansion of LUL102and LLL104, lesion60has moved downward in the chest cavity and away from the back109of patient100, to locate substantially along a midline (not shown) of radiation beam130. Empty circle61inFIG. 1Bindicates where lesion60was located at the earlier, full exhalation stage of the respiratory cycle of patient100shown inFIG. 1A. Density of shading of LUL102and LLL104is reduced inFIG. 1Brelative to density of shading of LUL102and LLL104inFIG. 1A to indicate that expansion of the lungs has reduced lung tissue density relative to lung tissue density at full exhalation.

FIG. 1Cschematically shows patient100when the patient's respiration has progressed from the middle of the inhalation portion of the respiration cycle shown inFIG. 1Bto a state at which the patient has fully inhaled. Diaphragm110is maximally contracted and drawn inferiorly to expand chest cavity106and the lungs to their respective maximum volumes and inspire air to fully fill the lungs. Density of lung tissue in the fully expanded lungs is substantially at a minimum and is schematically indicated by the relatively sparse shading of LUL102and LLL104inFIG. 1C. As a result of motion of diaphragm110, associated motion of the rib cage and expansion LUL102and LLL104, lesion60has displaced further downward in the chest cavity106and away from the back to a position along a left edge108of beam130. InFIG. 1Copen circles61and62indicate positions of lesion60at the earlier stages of the respiratory cycle of patient100shown respectively inFIGS. 1A and 1B.

Following full inhalation as shown inFIG. 1C, diaphragm110relaxes to retrace in reverse its motion shown inFIG. 1AtoFIG. 1Cand cause chest cavity to contract and expel air from the lungs in an exhalation portion of the respiratory cycle of patient100. When fully relaxed, exhalation is complete, diaphragm110is returned to its fully elevated position in chest cavity106shown inFIG. 1Aand patient100is ready again to initiate inhalation and begin a new respiratory cycle. During exhalation, in sympathy with motion of diaphragm110and contraction of chest cavity106, lesion60reverses its motion and retraces its trajectory backwards to move from its location inFIG. 1C, through the location indicated by open circle62, to the location of lesion60shown inFIG. 1Aand indicated inFIG. 1Cby open circle61.

With each complete respiratory cycle, from initiation of inhalation through completion of exhalation, lesion60executes round trip motion from its location inFIG. 1Ato its location inFIG. 1Cand back to its location inFIG. 1A. A boundary64inFIG. 1Csurrounds empty circles61and62and lesion60and encompasses the round trip trajectory of lesion60. Boundary,64represents a boundary of an internal target volume, ITV, for lesion60. Numeral64may be used to refer to the ITV bounded by boundary64as well as the boundary. The size of radiation beam130and the size of ITV64are substantially dictated by the size of the GTV of lesion60and a constraint to maintain the lesion within radiation beam130during the respiration cycle of patient100. The size of radiation beam130and the size of ITV64inFIGS. 1A-1Cindicates that in addition to the GTV of lesion60, a substantial volume of the patient's healthy tissue is exposed to potentially damaging radiation during treatment.

FIG. 2schematically shows a Steady-Site ACCURAD apparatus20for providing radiation therapy, in accordance with an embodiment of the invention. In the figure ACCURAD20is schematically shown treating patient100for the same lesion60of LLL104shown inFIGS. 1A-1C.

Steady-Site ACCURAD20optionally comprises a radiation beam generator22, a CPAP apparatus40, and a controller50that controls the radiation beam generator and the CPAP apparatus. CPAP apparatus40optionally comprises a face mask42, shown mounted to the face of patient100and connected by a flow tube44to an air pump system46. The air pump system is controllable by controller50to provide a flow of breathable gas such as air at a desired pressure and flow rate to the face mask and thereby to patient100via flow tube44. Optionally, CPAP apparatus40is controllable to provide a flow of gas to face mask42other than a conventional mix of gases found in air. For example, controller50may control air pump system46, in accordance with an embodiment of the invention, to provide a mix of gases to face mask42having higher or lower oxygen content than ambient air. Optionally, controller50controls air pump system46to provide a desired humidity and/or temperature of gases that flows to face mask42. Gas flow under any suitable condition of pressure, flow rate, temperature and humidity, and any suitable mix of gases provided to a patient, such as patient100, by a CPAP apparatus in accordance with an embodiment of the invention, may be referred to a CPAP gas flow or CPAP airflow.

To provide a desired dose of radiation to lesion60, controller124controls CPAP apparatus40to provide an optionally constant CPAP gas flow of air to face mask42at a pressure and flow rate sufficient to substantially fully expand the lungs of patient100and moderate motion and position of diaphragm110, the lungs, and other internal organs of the patient's chest cavity, and thereby motion of lesion60, during respiration. The fully expanded lungs have a relatively low lung tissue density that may be substantially equal to the low lung tissue density represented inFIG. 1C. The low lung tissue density is indicated inFIG. 2by the density of shading of LUL102and LLL104, which is the same as the density of shading of LUL102and LLL104inFIG. 1C.

Following initiation of CPAP airflow to patient100, controller50controls beam generator22to generate a beam30of radiation that is aimed at lesion60. Since provision of the CPAP airflow in accordance with an embodiment of the invention moderates motion of lesion60, the lesion is associated with an ITV, a “CPAP-ITV”, schematically indicated by a border70, that is smaller than ITV64associated with lesion60(FIG. 1C) when the lesion is treated by a conventional radiology machine such as radiology machine120(FIGS. 1A-1C). As a result, radiation beam30provided by Steady-Site ACCURAD20in accordance with an embodiment of the invention, may be characterized by a solid angle that is relatively small compared to the solid angle of beam130. Therefore, as schematically shown in the plane ofFIG. 2, radiation beam30generated by Steady-Site ACCURAD20to treat lesion60has an opening angle φ relatively small compared to the opening angle θ of radiation beam130(FIGS. 1A-1C) generated by conventional radiology machine120.

As a result of its relatively small solid angle, a volume of healthy tissue in patient100that is exposed to potentially damaging radiation from ACCURAD radiation beam30provided by Steady-Site ACCURAD20is relatively small compared to a volume of healthy tissue exposed to radiation from conventional radiation beam130.

By way of a numerical example, conventional X-ray radiation machine120may irradiate a lesion60with radiation beam130of X-rays (FIG. 1A-1C) from a distance of about 100 cm (centimeter). The lesion may have a determined ITV64characterized by maximum dimension equal to about 10 cm perpendicular to a direction of propagation of X-ray beam130. The X-ray beam may therefore have an angle θ ( ) in the plane ofFIGS. 1A-1Cequal to about 5.7°. For the same lesion60, CPAP-ITV70determined for Steady-Site ACCURAD radiation machine20(FIG. 2) may have a maximum dimension perpendicular to ACCURAD radiation beam30provided by ACCURAD equal to about 7 cm. In the plane ofFIG. 2, ACCURAD radiation beam30may therefore have an angle φ (FIG. 2) equal to about 4.0°.

In an embodiment of the invention, a Steady-Site ACCURAD apparatus, similar to ACCURAD20, comprises a medical imager (not shown) operable to image, an optionally malignant, lesion of a patient to be treated by ACCURAD. The imager may use any of various suitable medical imaging modalities to image the lesion. By way of example, the medical imager may image the lesion using one, or any combination of more than one of MRI (magnetic resonance imaging), flouroscopy, CT (computed tomography), PET (positron emission spectroscopy), SPECT (single photon emission computed tomography), or ultrasound scanners. ACCURAD may operate the medical imager to image the lesion while controller124controls CPAP apparatus40to provide CPAP airflow to the patient that expands the patient's lungs and moderates motion of the patient's diaphragm, and the lesion. A processor optionally comprised in controller124processes the images to identify the lesion and determine the moderated motion of the lesion during provision of CPAP airflow to the patient. The processor may determine a CPAP-ITV, for example CPAP-ITV70shown inFIG. 2, that is used to configure a beam of radiation for treating the lesion, responsive to the identified lesion and imaged moderated motion.

FIG. 3presents a flow diagram200of simplified procedure in accordance with which a Steady-Site ACCURAD apparatus may operate to deliver therapeutic radiation to a target site of a patient's body.

In a block202Steady-Site ACCURAD20provides CPAP airflow to the patient. Optionally in a block204while the patient is experiencing CPAP airflow Steady-Site ACCURAD acquires images of a region of interest (ROI) in the patient's body. In a block206the images are processed to identify a target site in the ROI to be treated with radiation provided by Steady-Site ACCURAD and determine motion of the target site during respiration. Optionally in a block208a CPAP-ITV is determined for the target site and in a block210the target site is irradiated with radiation provided by Steady-Site ACCURAD responsive to the CPAP-ITV.

Whereas in the above description radiation beam30provided by ACCURAD20may be considered by omission as being a static beam that is substantially unchanged during irradiation of lesion60, practice of an embodiment of the invention is not limited to static radiation beams. For example, an ACCURAD radiation beam may be shuttered in synchrony with motion of a lesion within a CPAP-ITV to irradiate the lesion at a same location within the CPAP-ITV substantially only when the lesion moves through the location. Alternatively or additionally, an ACCURAD radiation beam may be controlled to track a lesion during its motion within a CPAP-ITV.

The above description describes irradiating a lesion during provision of CPAP airflow and imaging a patient's lesion using any of various imaging modalities and CPAP airflow. However, practice of an embodiment of the invention is not limited to therapeutic radiology or medical imaging of lesions. A Steady-Site apparatus in accordance with an embodiment of the invention may for example be used to stabilize a tissue in a target site in a patient's body to facilitate performing a biopsy of tissue in the target site, or to carry out radiofrequency or MRI focused ultrasound ablation of tissue in the target site. A Steady-Site apparatus may be advantageous for use in stabilizing an organ during a medical procedure such as by way of example, stabilizing heart motion during valve replacement or catheterization of the heart or catheterization and/or stent deployment of blood vessels in or connected to the heart. Generally catheterization of a target site, such as the heart or a blood vessel is preformed while imaging the target site. Providing CPAP during catheterization, as noted above, may improve resolution of the imaging by reducing motion of the target site, increasing distance of the target site from adjacent organs, and/or increasing contrast of the target site relative to surrounding tissue. The improved resolution may enable reduction of a radiation dose and/or a quantity of contrast or isotope to which the patient may be exposed to effect the imaging.

There is therefore provided in accordance with an embodiment of the invention, apparatus for performing a procedure at a target site of a patient's body, the apparatus comprising: a continuous positive airway pressure (CPAP) apparatus that provides CPAP to the patient's lungs; a medical device for performing the procedure at the target site; and a controller that controls the CPAP apparatus to provide CPAP to the patient's lungs during performance of the procedure. Optionally, the medical device comprises a radiation beam generator that generates a radiation beam for irradiating tissue at the target. Optionally, the radiation beam generator configures the radiation beam to irradiate an internal target volume (ITV) in the patient's body that comprises the target site. The ITV may be determined responsive to an image of the target site acquired by a medical imager during provision of CPAP to the patient's lungs. The apparatus may comprise a medical imager that acquires the image of the target site. The controller optionally comprises an executable instruction set that the controller executes to process the image to determine the ITV.

In an embodiment of the invention, the medical device comprises a tissue ablator that delivers energy to tissue in the target site to ablate the tissue.

In an embodiment of the invention, the medical device comprises a biopsy sampler that operates to acquire a sample of tissue in the target site.

In an embodiment of the invention, the medical device comprises a catheter.

In an embodiment of the invention, the medical device comprises a stent.

In an embodiment of the invention, the medical device comprises a medical imager.

In an embodiment of the invention, the medical device comprises a robotic device controlled by the controller.

In an embodiment of the invention, the medical device comprises a manually operated medical device.

There is further provided in accordance with an embodiment of the invention method of performing a procedure at a target site of a patient's body, the method comprising: providing continuous positive airway pressure (CPAP) to the patient's lungs; and performing the procedure at the target site during provision of CPAP to the patient's lungs.

Optionally, the procedure comprises irradiating the target site with radiation. Optionally, the method comprises determining an internal target volume (ITV) for the target site that is illuminated by the radiation. Optionally, determining the ITV comprises acquiring an image of the target site during provision of CPAP to the patient's lungs and determining the ITV responsive to the image.

In an embodiment of the invention, the procedure comprises performing a biopsy of tissues at the target site. In an embodiment of the invention, the procedure comprises ablating tissue at the target site. In an embodiment of the invention, the procedure comprises imaging tissue at the target site. In an embodiment of the invention, the procedure comprises catheterizing the target site

In an embodiment of the invention, the procedure comprises performing a biopsy of tissues at the target site. In an embodiment of the invention, the procedure comprises ablating tissue at the target site. In an embodiment of the invention, the procedure comprises imaging tissue at the target site. In an embodiment of the invention, the procedure comprises catheterizing the target site.

Descriptions of embodiments of the invention in the present application are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments utilize only some of the features or possible combinations of the features. Variations of embodiments of the invention that are described, and embodiments of the invention comprising different combinations of features noted in the described embodiments, will occur to persons of the art. The scope of the invention is limited only by the claims.