WO2007044469A2

WO2007044469A2 - A method and apparatus to direct radiation treatment to a specific region of the brain

Info

Publication number: WO2007044469A2
Application number: PCT/US2006/038981
Authority: WO
Inventors: Albert S. Kyle; Ulrich Herken
Original assignee: Perfusion Technology, Llp
Priority date: 2005-10-05
Filing date: 2006-10-05
Publication date: 2007-04-19
Also published as: WO2007044469A3

Abstract

A system and method are provided for delivering radiation therapy to a target inside the head of a patient. A first reference coordinate system is defined in relation to anatomical landmarks on the patient's head which are visible externally and in images of the patient. The coordinates of a target are translated from the first reference coordinate system to a second reference coordinate system. The second reference coordinate system is defined in relation to an external locator device that is attached to the patient's head. The system comprises a treatment cap, locator device, sensor, ultrasound transducer, holder, and a variety of computer readable media. Angles are calculated to direct radia- tion to the target from the external locations selected with the locator device. Further, a treatment cap is produced that fits around the patient's head and holds interface units at certain positions and orientations. Each interface unit includes a movable transducer holder that holds a radiation source, and by rotating the transducer holders by the calculated angles, radiation is delivered to the target.

Description

A METHOD AND APPARATUS TO DIRECT RADIATION TREATMENT TO A SPECIFIC REGION OF THE BRAIN

BACKGROUND OF THE INVENTION

Field of the Invention This invention relates to delivery of radiation therapy, such as therapeutic ultrasound radiation, to an internal site in a patient, for example, for treatment of neurological diseases and disorders.

Background Information

Currently available radiation therapy techniques are known to be helpful in treat- ing neurological diseases, including brain tumors. Unfortunately, radiation therapy employs ionizing radiation and/or nuclear methods. These are known to produce harmful complications, including leukoencephalopathy and brain atrophy, leading to neurocogni- tive deterioration and dementia; brain necrosis, resulting in more specific neurologic sequelae; and communicating hydrocephalus, causing cognitive, gait, and bladder dysfunc- tion. In addition, present methods and devices for use in radiation therapy are large and costly. Cost and size are practical limitations to the availability of the therapy.

Directing the radiation only to the desired site is critical in limiting the complications of radiation therapy. Stereotactic Radiosurgery (SRS) is one technique for external radiation that utilizes multiple convergent beams to deliver a high single dose of radiation to a radiographically discrete treatment volume. SRS can be performed with high-energy x-rays produced by linear accelerators, with gamma rays from a gamma knife, and, less frequently, with charged particles, such as protons, produced by cyclotrons. SRS radiation is expensive, costly and complex, and can cause many of the side effects described above.

In order to direct radiation to a desired site in a patient (hereinafter a target), it is necessary to locate the target from outside of the patient using images of the inside of the patient that show the anatomical structures at the site. Prior techniques to accomplish this generally may be classified as either head fixation techniques and/or localization techniques.

External head fixation techniques completely immobilize a patient in space, e.g. on an imaging platform of a device such as a Computed Tomography (CT), Magnetic Resonance Imaging (MRI), or Positron Emission Tomography (PET) scanner. During the imaging procedure, the spatial position of a target inside the patient is determined relative to the imaging platform itself. A localizing device is articulated (i.e. movably attached) from the imaging platform and uses the same reference coordinate system as the platform. Examples of this method may be found in U.S. Patent No. 5,427,097 to Depp titled "Apparatus for and Method of Carrying Out Stereotaxic Radiosurgery and Radiotherapy," and U.S. Patent No. 6,275,564 to Ein-Gal titled "Positioner for Radiation Treatment," among other patents. While these types of devices are suitable in some radiation therapy applications, they are not suitable when a patient must be moved between imaging and the therapeutic procedures. This shortcoming accordingly limits their use. Localization techniques create a reference system during imaging that is associated with the patient, not with the imaging device. Directing treatment to a predetermined target by means of a reference system is commonly referred to as stereotaxis. The development of CT technology, MRI, angiography, digital subtraction angiography (DSA) and similar diagnostic procedures for producing images of structures contained within tissue has been applied to the field of stereotaxis to produce image-directed stereotaxis. A stereotactic apparatus is used in conjunction with diagnostic imaging to produce internal images keyed to either a Cartesian or polar coordinate system. When the same stereotactic apparatus is utilized during treatment as was used in imaging, it is possible to access a precise position inside the skull identified on the diagnostic images on the basis of the same coordinate system. Such image-directed stereotactic procedures involve, generally, the steps of:

(1) establishing a stereotactic space incorporating all areas of the cranial structure under investigation by means of a rigid external framework positioned in fixed relationship to the skull; (2) performing a diagnostic imaging procedures with the framework in place, so that any lesion or other intracranial structure identified by the imaging procedure can be located in precise relationship to the fixed external framework and its position recorded on the basis of a coordinate system related to the stereo- tactic framework; and

(3) utilizing the same external stereotactic framework and coordinate system during the therapeutic procedure to guide the treatment to the precise location inside the cranium where an effect is required.

Various stereotactic framework systems are in use throughout the world, the most popular systems being the Brown-Roberts- Wells (BRW) stereotactic system available from Radionics, Inc. of Burlington, Massachussets, the Cosman-Roberts- Wells (CRW) system also available from Radionics, Inc. of Burlington, MA, and the Leksell stereotactic system available from Elekta Instruments of Stockholm, Sweden. The BRW, CRW, Leksell and other systems utilize an external headring that is rigidly attached to the pa- tient's skull by means of extensible pins. A localizing device with vertical and inclined rods may be attached to the headring during imaging procedures. Computer software may translate information from diagnostic images with the head ring and localizing device in place into X, Y, and Z coordinates of a point inside the skull. Subsequently, during a therapeutic procedure, while the fixed headring is still in place, the localizing device is removed and an arc or other placement device attached to the headring. The arc or other placement device directs radiation therapy to the point defined by the X, Y and Z coordinates relative to the headring.

A significant shortcoming of known localization techniques is that the stereotactic framework must be attached during imaging so that any lesion or other target identified can be located in relationship to the framework. To partially address this issue, prior efforts have been directed at making a stereotactic framework removable and replaceable. Yet this does not address the underlying issue that the framework must be in place at both the time of imaging and the time of treatment.

For example, a localization device that has a removable and replaceable steriotac- tic framework has been developed by Lauri Laitinen of Sweden, and is known as the "La- itinen Stereoadapter." The device is removably attached in an exactly reproducible position to the patient's head by reference to the patient's nose bridge and ears, so that it can be applied, removed, and then reapplied precisely. The Laitinen stereoadapter incorporates fiducial markers that can be related to CAT images, MRI images, DSA, or other im- ages to establish an intracranial coordinate system. Since the device is designed to be removed and reapplied precisely, coordinates obtained at the time of imaging are used at the time of treatment. With the Laitinen Stereoadapter, a patient could, for example, have a computed axial tomography (CAT) scan done one day, an angiogram done another day, and the actual therapeutic procedure performed on a third day. Yet while this is an im- provement over non-removable stereotactic frameworks, the framework must still be in place at the time of imaging and treatment and thus the true shortcoming is not addressed.

Accordingly, there is a need therefore for a new system and method for providing radiation therapy to a patient, for example to direct radiation treatment to a specific region of the brain, which avoids the shortcomings of present devices, while minimizing the cost, size, and complications described above. Such a system and method should address the shortcoming of known systems in that they require a patient to remain in a fixed position on a platform or have a stereotactic framework in place at both the time of imaging and of treatment. An improved system would allow treatment to be delivered based upon existing CT or MRI images of a patient, with no need for special imaging of the pa- tient with a stereotactic framework in place.

SUMMARY OF THE INVENTION

A system and method are provided for delivering radiation therapy to a target in- side the skull of a patient, without requiring the patient to remain in a fixed position on a platform, or wear a localization device during imaging. Images of the head of the patient, which show the target, are acquired using a conventional imaging system, such as a CT or MRI system. A first reference plane is defined by reference points associated with anatomical landmarks on the patient's head that are visible externally and in internal im- ages of the patient. From this first reference plane, a first reference coordinate system is created, and the target is defined in relation to the origin of this first reference coordinate system. A locator device is then applied externally to the head of the patient. The locator device also references the external anatomical landmarks and accordingly is related to the first reference coordinate system. The locator device includes a rotating guide, a sliding guide, a movable rod, as well as other structures that permit a contact plate to be placed at a precisely determinable position (i.e. a location on the patient's head) and orientation (i.e. a rotation about an axis normal to the surface of the patient's head) on the patient's head. A second reference plane is established in reference to the contact plate, and from this, a second reference coordinate system is established whose origin is defined in relation to the contact plate. Using a series of mathematical rotations and shifts, the coordinates of the target in the first reference coordinate system are translated to coordinates in the second reference coordinate system. From these coordinates, an angle thetct that represents a rotation parallel to the contact plate and an angle phi that represents an eleva- tion in relation to the contact plate are determined. Such angles, together with the position and orientation of the contact plate, are used to direct radiation to the intended treatment target.

The delivery of radiation to the target may be facilitated by further aspects of the disclosure, which relate to a treatment cap, associated structures, and methods for their use. A flexible generally head-conforming treatment cap (e.g., a cap of a thin latex similar to that used for swimming caps, or of another suitable material) is provided. The locator device may be secured over the treatment cap and the contact plate of the locator device placed at a precisely determined position and orientation on the cap corresponding to the place where radiation is to be delivered into the head of the patient. Using the contact plate as a stencil, the treatment cap is marked. At each marked position and orientation on the treatment cap, an interface unit is inserted. The interface unit includes a movable transducer holder that holds a radiation source. The movable transducer holder may be rotated by angles theta and phi, after which, when the cap is in place on the patient's head, radiation will be precisely delivered to the target. In some embodiments, the inter- face unit also may include a material especially suited to enhance propagation of radiation from the transducer to the target, for example a hydrogel. The interface unit may also include a means to determine the qualities of the radiation delivered to the patient. Advantageously, the cap may readily be removed between treatments and later replaced.

BRIEF DESCRIPTION OF THE DRAWINGS

The description below refers to the accompanying drawings, of which: Fig. 1 shows a patient wearing an exemplary treatment cap according to an illustrative embodiment of the present disclosure;

Fig. 2a shows an interface unit with a main body and a movable transducer holder that holds a radiation source, according to an illustrative embodiment of the present disclosure; Fig. 2b shows the interface unit of Fig. 2a where the movable transducer holder has been repositioned at an angle relative to the position of Fig. 2a;

Fig. 3 shows a cross section of an interface unit according to an illustrative embodiment of the present disclosure;

Fig. 4 shows a path of an exemplary ultrasound beam traveling through the con- tact material in the cross section of the interface unit according to an illustrative embodiment of the present disclosure;

Fig. 5a shows two images of a patient's head that illustrate a technique for creating a first reference plane and a corresponding first reference coordinate system from images of the patient; Fig. 5b illustrates an exemplary technique for determining the location of a target in an image of the patient;

Fig. 6a shows an exemplary locator device that includes a halo, a bridge of the nose locator, and an ear meatus locator that allows determination of the location and orientation of an interface unit in relation to the first reference coordinate system; Fig. 6b shows an enlargement of a portion of the exemplary locator device and provides further detail of the rotating guide, the sliding guide, and the contact plate; Fig. 7a shows an exemplary locator device placed over an exemplary treatment cap according to an illustrative embodiment of the present disclosure;

Fig. 7b shows an exemplary treatment cap that has been marked with an outline showing a position and an orientation for an interface unit; and Fig. 8 illustrates a conversion operation from Cartesian coordinates to spherical coordinates that may be employed to calculate values in accordance with an illustrative embodiment of the present disclosure.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE

EMBODIMENT The below detailed description describes a exemplary treatment device to deliver radiation, for example ultrasound radiation, to a target area in the brain of a patient and an exemplary locator device to reference locations inside and outside of the head of the patient to certain landmarks. Also described is an illustrative method for using these devices. Fig. 1 shows a patient wearing an exemplary treatment cap 100 according to an illustrative embodiment of the present disclosure. The treatment cap 100 is made from, for example, a thin latex similar to that used for swimming caps, or of another suitable material. During treatment, the patient wears the generally head-conforming treatment cap. The treatment cap 100 may be re-used during subsequent treatments of the patient, and disposed of when treatment is complete. Affixed into openings in the treatment cap 100 are one or more interface units 110 that each hold a radiation source. The interface units 110 may in some configurations be disposable. Each interface unit 100 is located at a desired position (i.e. a location on the patients head) and at a desired orientation (i.e. a rotation about an axis normal to the surface of the patients head) and includes a radiation source. In one embodiment, the radiation source may be an ultrasound transducer 120 with attached cable 130 that is inserted into the interface unit 110. The ultrasound transducer may be any of a variety of well-known types, for example, a piston type transducer, an annular array transducer, or a two-dimensional array transducer. The ultrasound radiation produced by such a transducer may be advantageously used for a variety of purposes. For example, the radiation may be used to assist delivery of a therapeutic or diagnostic agent to a particular target location, to which it is normally partially or substantially prevented from reaching due to barriers, for example a barrier between the blood stream and brain of the patient.

Fig. 2a shows an interface unit 110 with a generally hemispherical main body 200 5 and a movable transducer holder 210 that holds a radiation source, according to an illustrative embodiment of the present disclosure. In this embodiment, the direction of the radiation source may be changed in two ways. First, the transducer holder 210 may be rotated in a plane normal to the approximately-flat base of the hemispherical main body 200. For example, Fig. 2a shows the transducer holder 210 positioned at approximately a Q 90-degree angle to the flat base of the main body 200 (this angle is hereinafter referred to angle phi) such that radiation emitted from the ultrasound transducer 120 is directed substantially normal to the base of the main body 200. A coiled wire 230 establishes a flexible electrical connection between the transducer holder 210 and devices housed in the main body 200, thereby allowing signals to pass there-between.

s Second, the radiation source may be rotated in a plane parallel to the base of the main body. The main body is attached to a rotating rim 240 that has a number of protuberances for contacting the patient's head, for example contact pins, ridges, or other projecting structures. Fig 2a shows three contact pins 260 (only two of which are visible in this perspective view) for contacting the patient's head. The rotating rim 240 allows the Q main body and to the contact pins 260 to rotate by a selected angle (this angle hereinafter is referred to as angle thetά). An angle indicator 250, in conjunction with angle markings 220 on the main body 200, indicates the selected angle theta.

Fig. 2b shows the interface unit 110 of Fig. 2a where the movable transducer holder 210 has been repositioned at an angle relative to the position shown in Fig. 2a. 5 The angle phi of this rotation is indicated by the now exposed angle markings 280 on the main body 200. The coiled wire 230 is shown in a more extended position to maintain the electrical connection between the transducer holder 210 and devices in the main body 200. Fig. 3 shows a cross section of an interface unit 110 according to an illustrative embodiment of the present disclosure. In this embodiment, the main body 200 is filled with a contact material 300 that is highly conductive to ultrasound, for example a hy- drogel contact material. The contact material 300 may extend beyond the main body 200 so that its surface 301 is at least in line with the end of the contact pins 260 (only one of which is shown), to thereby allow the contact material to contact the patient's head. In this embodiment, the shape of the main body 200 and contact material 300 is hemispherical, with the center of the surface of the contact material 301 being the center of the hemisphere. However, it is contemplated that a differently shaped main body 200 and contact material 300 may be advantageously employed. For example, in another embodiment a contact pad may be employed to conduct the ultrasound to the patient.

In some embodiments, to monitor the quality of the radiation delivered, a sensor 310 may be embedded in the contact material. The sensor 310 may be adapted to sense pressure fluctuations caused by ultrasound waves, so as to measure both original radia- tion intensity, and intensity of reflected radiation, to thereby provide information about the quality of radiation transmittance. In one configuration, the sensor is made from a PolyVinylidine DiFluoride (PVDF) film which generates an electrical signal in response to the pressure fluctuations caused by the ultrasound waves. The electrical signal may be sampled at different times to detect various signals and reflections. However, the sensor need not be made from a PVDF material, and other configurations may employ a variety of other well-known materials and sensor designs. The sensor 310 may pass electrical signals to the transducer holder 210 via the insulated wire 230, where they may thereafter be passed to external monitoring equipment (not shown).

Fig. 4 shows a path 410 of an exemplary ultrasound beam traveling through the contact material 300 in the cross section of the interface unit 110 according to an illustrative embodiment of the present disclosure. The exemplary ultrasound beam emanates from the ultrasound transducer 120. In some configurations, the ultrasound beam passes through the sensor 310 at a first location 411 on its way towards the patient. As the ultrasound beam passes through the sensor 310, a first electrical signal (not shown) may be generated by the sensor 310. This first electrical signal provides a measure of the original radiation intensity. Because of the hemispherical shape of the main body 200 and the contact material 300, the center of the ultrasound beam impacts the center of the contact surface 301 where a first portion of the beam is transmitted into the head of the patient.

A second portion of the ultrasound beam is reflected from the patient (e.g., from the patient's skull) in a backward direction along path 420, or a slightly different path

5 (not shown), and impacts the sensor 310 at a second location 421 creating a second electrical signal (not shown). Depending on the quality of the contact between the contact surface 301 and the patient, a third portion of the beam may form a backward directed reflection, back along path 420. This third portion of the beam may impact the sensor 310 at a approximately location 421, creating a third electrical signal (not shown). The Q second and third electrical signals, alone or through comparison with the first electrical signal, may be used to provide information about the quality of radiation transmittance, for example, to measure of the percentage of originally delivered radiation that enters the head of the patient.

In order to treat a target (e.g. a tumor or lesion) inside of a patient's brain, it is s necessary to identify the position of the target in images of the patient (e.g. CT scans,

MRI scans or other types of images), and then translate the position in these images into a position that may be used with an interface unit 110. According to an illustrative embodiment of the present disclosure, a first three-dimensional reference coordinate system is established and mapped onto images of the patient. The first reference coordinate sys- Q tern is established by creating a first reference plane that includes anatomical landmarks that can be readily identified externally, as well as in the images of the patient, hi the illustrative embodiment discussed below, three anatomical landmarks are used, yet it is contemplated that a greater or lesser number of landmarks may be employed with this technique. Further, in the particular illustrative embodiment discussed below, the ana- 5 tomical landmarks are selected to be the right and left external meatus of the ears (i.e. the openings of the ear canal) and the bridge of the nose. However, other anatomical landmarks may alternately be selected as reference points, for example the eyes, the nuchal protuberance, certain teeth, certain jaw bones, etc.

Fig. 5a shows two images 500, 501 of a patient's head that illustrate a technique Q for creating a first reference plane and a corresponding first reference coordinate system from images of the patient. The bridge of the nose is identified as a first anatomical landmark 510 in the first image 500. The exact image position of the first anatomical landmark is determined from position information 540 provided with the image 500 and the position defines a first reference point. Next, the right and left external ear meatus 521, 522 are identified as second and third anatomical landmarks, respectively, and define second and third reference points. A triangle 530 is envisioned connecting the three reference points, and this triangle defines the first reference plane. Further, the line of the triangle connecting the two external ear meatus is selected as the X-axis of the first reference coordinate system. The center of the line connecting the two external ear meatus is selected as the origin of the first reference coordinate system. A line passing through the origin at a 90-degree angle to the X-axis and co-incident with the first reference plane is selected as the Y-axis. Finally, another line passing through the origin at an angle of 90- degrees relative to both the X-axis and the Y-axis is selected as the Z-axis of the first reference coordinate system. Since images may be generated in planes that are not exactly parallel to the first reference plane, to accurately determine a position of a target, an offset may be needed to adjust one or more of the reference points so that the first reference plane is exactly parallel to the images. For example, the first reference plane might be tilted to a position that is parallel to the images by adding a positive or negative offset delta to the Z-axis coordi- nate of the first reference point (the one corresponding to the bridge of the nose). In one embodiment, an appropriate delta may be calculated by subtracting position information 540 descriptive of the Z-axis location of the first reference point, from position information 541 descriptive of the Z-axis location of a different reference point (e.g., either of the second or third reference points). For example, using the exemplary values show in Fig. 5a, a 17.5 mm position is subtracted from a 47.5 mm position to yield a negative delta of 30 millimeters, which later may be applied to the first reference point to align the first reference plane parallel to the images.

Furthermore, once calculated, the offset delta may readily be converted into a correction angle gamma that is useful in later calculations discussed below. The correc- tion angle gamma is calculated by measuring a distance (referred to hereinafter as "/') 523 of the first reference point corresponding with the bridge of the nose from the origin of the coordinate system, and thereafter applying the formula gamma = tan (delta Iy). Thus when gamma is later discussed, the reader should refer to this formula.

After establishing the first reference coordinate system, and possibly adjusting it to be parallel to an image plane, the location of one or more treatment targets is deter-

5 mined relative to the origin of the first reference coordinate system. Fig. 5b illustrates an exemplary technique for determining the location of a target 550, hi this instance a tumor, in an image 503. First, the intercept of the Z-axis of the first reference coordinate system with the image plane is marked on the image 503 at a point 535. The distance of the target 550 from that point 535 is measured as an X-axis distance 560 and as a Y-axis dis- o tance 570. Also, a distance to the target along the Z-axis is determined by subtracting position information 541 descriptive of the Z-axis location of the origin of the first reference coordinate system, from position information 542 descriptive of the target's Z-axis location. For example, using the exemplary values show in Fig. 5a and Fig. 5b, the image showing the target indicates a Z-axis position of 32.5 mm and the image showing the 5 origin indicates a Z-axis position of -47.5 mm, which yields a total Z-axis distance of 80.0 mm.

In an alternate embodiment, the distance of the target 550 from the origin 531 along the Z-axis may be determined by counting a number of image slices taken by the imaging system, between the slice that includes the origin and the slice that includes the 0 target, and then multiplying the number of slices by a known slice thickness, hi such a manner, the techniques described herein may be applied to older imaging systems that lack some of the capabilities of more modern imaging systems, e.g., the provision of Z- axis position measurements.

In another alternate embodiment, various built-in tools provided with an imaging 5 systems may be employed to simplify the above described calculations and measurements. Such tools may be used to manipulate image data into differing forms that streamline calculations.

Once the location of the target is determined in reference to the first reference coordinate system, it is necessary to determine the location at which an interface unit 110 is o to be located in reference to the first reference coordinate system. The desired location of an interface unit 100 may vary depending on various criteria. For example, the location may be selected to minimize the bone thickness that radiation must pass through, or to avoid certain regions of the brain. Such criteria, in combination with individual variations in skull shape and size for each patient, cause there to generally be no "standard" s positions for interface units, and accordingly it is highly advantageous to allow a physician to locate an interface unit at any location on a patient's head using an individualized location technique.

Fig. 6a shows an exemplary locator device 600 that includes a halo 605, a bridge of the nose locator 610, and ear meatus locators 620 (only one of which is visible in this G perspective view) that allows measurement of the location and orientation of an interface unit in relation to the first reference coordinate system. As discussed above, the selection of the bridge of the nose and the two ear meatus as anatomical landmarks is simply for illustrative purposes and other landmarks could be selected. Each of the locators is precisely aligned to its corresponding anatomical landmark on the patient. The halo 605 s connects the locators and creates a plane that includes the bridge of the nose locator 610 and the two external ear meatus locators 620 (only one of which is visible in Fig. 6a). A semi-circular rotating guide 630 rotates forward and backwards around an axis extending through the two external ear meatus locators 620, and its angular position is indicated on an angle indicator 640. To compensate for adjustment of the first reference plane to ac- G commodate the orientation of the image slices, discussed above in reference to Fig. 5a, the angular scale itself may be adjusted relative to the halo 605 by the correction angle gamma. Thus the above described first reference plane from the images may be physically replicated using locator device 600.

A sliding guide 650 moves on the rotating guide 630. In this manner the sliding 5 guide can be rotated to a known position about the origin of the first reference coordinate system. The sliding guide 650 holds a movable rod 660 that points towards the origin.

The movable rod 660 can move up and down in the sliding guide. A contact plate 670 is disposed at the end of the movable rod 660, and is adapted to contact the patient's head.

The diameter of the contact plate may advantageously be similar or equal to the diameter G of the main body 200 of the interface unit 110 shown in Figs. 2a and 2b. While Fig. 6a shows a single rotating guide 630 having a single siding guide 650 and associated assembly, it should be remembered that this is not a limitation of the present disclosure. A multiplicity of rotating guides may be attached to the halo 605, and also a multiplicity of sliding guides may be attached to each rotating guide, hi a configu- ration where multiple rotating guides are employed, adjacent rotating guides may be positioned such that the movable rods face each other, to allow closer placement.

Fig. 6b shows an enlargement of a portion of the exemplary locator device 600 and provides further detail of the rotating guide 630, the sliding guide 650, and the contact plate 670. Angle markings 631 on the rotating guide 630 allow measurement of the angular position of the sliding guide 650 with a marker 651. The movable rod 660 can rotate in the sliding guide and its rotational angle is indicated by additional angle markings 653 that are pointed to by a marker 652. The movable rod 660 can also move longitudinally through the sliding guide and its longitudinal position is identified by the distance markings 661 on the movable rod 660. Further the contact plate 670 mounted at the end of the movable rod 660 is affixed such that it can rotate about an axis normal to the movable rod 660. The angular position of the contact plate 670 is indicated by the angle markings 675 on an arch 671, which is affixed to the contact plate 670. A position indicator 672 protrudes from the contract plate on one side in extension of an imaginary line connecting the two ends of the arch. A separable ring 680, which may be detached by unfastening a connection screw or other fastening system, is fitted to the contact plate 670. The separable ring 680 in the illustrative embodiment has protuberances for contacting the patient's head, for example three contact pins (not shown) arranged on the underside (patient side) of the ring similar to the example contact pins found on the interface unit 110 shown in Fig. 2a and 2b. When the contact pins are placed in contact with a patient's head, the contact plate is oriented in the same manner as an interface unit 110 would be when radiation is being administered. Since the radiation source directs treatment to the center of the interface unit, the location of the center of the contact plate (hereinafter the contact point) coincides with the location at which radiation will enter the patient. The contact point may readily be represented in terms of angles measured with the locator device 600 and the offset of the first reference plane. Specifically, the angle (hereinafter alpha) at which the rotating guide 630 is disposed in relation to the head ring 605 is indicated on the angle indicator 640. The angle alpha represents an orientation in the YZ-plane (i.e. rotation about the X-axis) in the first reference coordinate system. The position at a right angle to the first reference plane is defined as 0-degrees, while positions to either side are represented as positive and negative angles.

Similarly, the angle (hereinafter beta) at which the sliding guide 650 is disposed in relation to the rotating guide 630 is indicated by a maker 651 and markings 631. The angle beta represents elevation from the YZ-plane (that is, rotation in the XZ-plane) of the first reference coordinate system. The position on the zenith of the rotating guide is defined as 0-degrees, and positions towards the right ear are negative angles, while positions toward the left ear are positive angles.

As explained in depth further below, the angles alpha and beta, along with measurements, are employed to translate the representation of the target in the first coordinate system into a representation in a second coordinate system that is based upon a second reference plane that is parallel to the contact plate 670, and thus to the contact surface of an interface units 110 that hold a radiation source. Such a second coordinate system is used to facilitate delivery of the radiation.

According to the illustrative embodiment, with the locator device of Fig. 6a and Fig. 6b affixed to the patient, a physician moves the contact point of the contact plate 670 to a location on the patients head where radiation is desired to enter. The physician then notes the angle readings for angles alpha and beta. Then the locator device 600 is removed from the patient, and the separable ring 680 removed from the contact plate 670. Thereafter, a treatment cap 100 is placed on the patient and the locator device 600 re- turned to its former position on the patient, yet now secured over the treatment cap 100.

Fig. 7a shows an exemplary locator device 600 placed over an exemplary treatment cap 100 according to an illustrative embodiment of the present disclosure. The contact plate 670 identifies the position and orientation at which an interface unit 110 is desired to be located in the treatment cap 100. The outline of the contact plate 670 is traced (e.g., using pencil, ink, etc.) onto the treatment cap, using the perimeter of the contact plate 670 as a stencil. This outline corresponds to the outline of the base of the hemispherical main body 200 of an interface unit 110.

Fig. 7b shows an exemplary treatment cap 100 that has been marked with an outline showing the position 700 and the orientation 710 (indicated by an extended marking) for subsequent placement of an interface unit. Using these markings, an appropriately positioned and oriented opening (e.g., a cut) is made in the treatment cap 100 for each interface unit 110, and the one or more interface units affixed in place for treatment of the patient.

According to an illustrative embodiment of the present disclosure, to determine the direction at which the radiation source of an interface unit 110 is to be pointed, values for angles theta and phi, previously discussed in relation to Fig. 2a and Fig. 2b, are calculated. To do so, the position of the target is determined in reference to a second reference plane that is parallel to the contact plate 670 of the locator device 600, and thus the contact surface of an interface unit 110. The previously discussed first reference coordinate system is rotated about its axes and its origin is shifted, to form a second reference coordinate system with an origin at the contact point and a Z-axis that coincides with the center of the movable rod 660, discussed above in reference to Fig. 6b.

The coordinates of the target are translated in accord with rotation and shift of the first reference coordinate system, to relate to the second reference coordinate system, by multiplying by appropriate rotation matrices. For example, the coordinates of a target (x',y',z⁵) after an α degree rotation about the X-axis are determined by multiplying the original coordinates (x, y, z) by the well-known rotation matrix:

Further, a shift along an axis of the coordinate system is performed by adding or subtract- ing an appropriate offset value.

Using these two mathematical techniques, the coordinates of the target are translated to relate to the second reference coordinates, according to the following sequence of steps. First, a rotation is performed about the X-axis by the angle alpha of the rotating guide described above. Second, a rotation is performed about the Y-axis by the angle beta of the sliding guide described above. Third, a shift of the origin along the Z-axis, which is now aligned to coincides with the center of the movable rod 660, is performed. The extent of the shift is determined by the distance between the origin of the first reference coordinate system and the tip of the movable rod 660, which may be calculated using the markings 661 on the movable rod 660. Forth, a rotation of the coordinate system about the Z-axis is performed, where the rotation angle is determined in response to the angle measurement on markings 652 that indicate the angle of the movable rod 660 in the sliding guide 650. Fifth, another rotation about the X-axis is performed using the angle of the contact plate 670 as measured by markings on the arch 671. After these five rotations and shifts are performed, the position coordinates of the target in the first reference coordinate system are effectively translated to be position coordinates in the second reference coordinate system. That is, the position coordinates now relate to a coordinate system whose origin and axes intersect at the contact point of the contact plate 670, and thus relate to an interface unit 110 placed at the same location and orientation as the contact plate.

Once the position coordinates of the target have been translated into coordinates in the second reference coordinate system, appropriate values for angles theta and phi are calculated, which describe how to direct radiation from the origin of the second reference coordinate system to the target. The angles thetα and phi were previously introduced in relation to Fig. 2a and the below further descriptions add to those above. In relation to the second reference coordinate system, angle thetα represents a rotation in the XY-plane. That is, angle thetα represents a rotation parallel to the contact plate 670 or the base of an interface unit 110 positioned on the patient. Similarly, in relation to the second reference coordinate system, angle phi represents an elevation angle from the XY-plane. That is, the angle phi represents an elevation in relation to the contact plate 670 or an interface unit 110 positioned on the patient.

Since the Cartesian (x,y,z) coordinates of the target in relation to the second refer- ence coordinate system are known, the values of angles thetα and phi may be calculated by a conversion from Cartesian coordinates to spherical coordinates. Fig. 8 illustrates a conversion operation from Cartesian coordinates to spherical coordinates that may be employed to calculate values of theta and phi in accordance with an illustrative embodiment of the present disclosure. The target 870 is shown in relation to the origin 800 of the second reference coordinate system and has known Cartesian co- ordinates. Accordingly, angle thetα 840 may be calculated by a conversion to spherical coordinates where Thetα = arctan (XfT), where X represents an X-axis distance 820 of the target and a Y represents a Y-axis distance 830 of the target. Similarly, angle phi 850 may be calculated as Phi = arctan (Z/ sqrt (X² + Y²), where X and Y are the same as above, and Z represents a Z-axis distance 810 of the target. Once calculated, the values of angles thetα and phi are used to rotate the movable transducer 210 of the interface unit 110 to administer radiation to the appropriate location. That is, referring again to Fig. 2a and Fig. 2b, the radiation from the radiation source is directed according to angle phi, using angle markings 280 and angle thetα, using angle markings 220, so direct the radiation to the target. The foregoing has been a detailed description of various illustrative embodiments of the present disclosure. While in many of the above descriptions, only a single interface unit 110 is shown, it should be remembered that multiple interface units may be employed in the treatment cap 100. For each interface unit 110, the above described determination of angles thetα and phi is repeated. When using more than one interface unit, and thus more than one radiation source, the radiation will advantageously intercept at the target, thereby creating an increased and localized effect.

Furthermore, various modifications and additions can be made to the above described illustrative embodiments without departing from the invention's intended spirit and scope. For example, it is contemplated that instead of creating an opening in a treat- ment cap, a cap-like structure may be formed on the head of the patient by casting, molding, layering, or other means of shaping adequate for the purpose. Such a cap-like structure formed on the head may use nose and ear meatus locators integrated into the structure to provide reference for the correct placement of the structure on the patient's head.

Also, it is contemplated that the calculations described above may be imple- mented wholly or partially in software (i.e., executable program instructions) stored on a computer-readable medium. A software implementation of the above described calculations may advantageously reduce the potential for human error. It is contemplated that in one possible software-based embodiment, data collected from the images and the angles indicated by the locator device may be inputted by an operator, and output provided auto- matically to the operator showing the required theta andphi angles. In an alternate software-based embodiment, the images may be electronically processed using image processing software and the angles from the locator device may be measured by electronic sensors. The electronic data may thereafter be electronically transmitted to, and processed by a computer system with executable program instructions configured to imple- ment the above described calculations.

Given the above discussed alternatives, and the other possibilities for other modification of the above techniques, the above description should to be taken only by way of example and not to otherwise limit the scope of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.

What is claimed is:

Claims

CLAIMS L A method for delivering radiation to a target inside of a patient, the method compris- ing the steps of: imaging the patient to acquire one or more images, at least one of which shows the target; establishing a first reference coordinate system based upon a plurality of external anatomical landmarks that are visible in the one or more images of the patient; representing the target as coordinates in the first reference coordinate system; selecting an external position on the patient from which to deliver radiation; establishing a second reference coordinate system based upon the external posi- tion; translating the coordinates of the target in the first reference coordinate system into coordinates in the second reference coordinate system; determining one or more angles from the external position to the target; and delivering radiation from the external position, the radiation directed according to the one or more angles to intercept the target inside the patient.

2. The method of claim 1, wherein the one or more images are selected from the group consisting of: Computed Tomography (CT) images, Magnetic Resonance Imaging (MRI) images, and Positron Emission Tomography (PET) images.

3. The method of claim 1, wherein the step of establishing a first reference coordinate system further comprises the step of: defining a first reference plane by three points, each of the points coinciding with one of the external anatomical landmarks of the plurality of external anatomical land- marks.

4. The method of claim 3, wherein the three external anatomical landmarks comprise the right external ear meatus, the left external ear meatus, and the bridge of the nose.

5. The method of claim 3, further comprising: adjusting the reference plane by adding an offset delta to one of the three points.

6. The method of claim 1, wherein the step of selecting an external position further com- prises the step of: placing a locator device on the patient in relation aligning a plurality of locators to the plurality of external anatomical landmarks.

7. The method of claim 6, wherein the step of selecting an external position further comprises the steps of: moving a contact plate to the external position; and determining the position of the contact plate in relation to the first reference coor- dinate system.

8. The method of claim 7, wherein the step of moving further comprises the steps of: adjusting a rotating guide to an angle alpha in relation to a head ring of the locator device; adjusting a sliding guide coupled to the rotating guide to an angle beta in relation to the rotating guide; and adjusting a movable rod coupled to the rotating guide and the contact plate by a particular distance.

9. The method of claim 8, wherein the step of translating the coordinates further com- prises the steps of: rotating the coordinates of the target about a first axis by the angle alpha; rotating the coordinates of the target about a second axis by the angle beta; and shifting the coordinates of the target along a third axis by the particular distance.

10. The method of claim 1 , wherein the step of establishing a second reference coordi- nate system further comprises the step of: selecting the origin of the second reference coordinate system to coincide with the external position.

11. The method of claim 1 , wherein the step of delivering radiation further comprises the step of: placing a treatment cap upon the patient, the treatment cap having a radiation source coupled thereto at the external position, the radiation source adjusted according to the one or more angles.

12. The method of claim 11, wherein the one or more angles comprise: an angle theta that represents a rotation in an first plane of the second reference coordinate system; and an angle phi that represents an elevation from the first plane of the second refer- ence coordinate system.

13. The method of claim 1, wherein the target is inside the head of the patient and the external position is on the surface of the head of the patient.

14. The method of claim 1, wherein the radiation is ultrasound radiation.

15. The method of claim 1, wherein the step of imaging is performed while a locator de- vice is absent from the patient and the step of selecting an external position, is performed by applying the locator device to the patient and manipulating the locator device.

16. A computer readable medium containing executable program instructions for deter- mining one or more angles at which to deliver radiation to a target inside of a patient, the executable program instructions comprising program instructions configured to: establish a first reference coordinate system based upon a plurality of external anatomical landmarks visible in one or more images of the patient, the target represented as coordinates in the first reference coordinate system; establish a second reference coordinate system based upon an external position on the patient selected from which to deliver radiation; translate the coordinates of the target in the first reference coordinate system into coordinates in the second reference coordinate system; and determine one or more angles from the external position to the target, such that radiation delivered according to the one or more angles will intercept the target inside the patient.

17. The computer readable medium of claim 16, wherein the one or more images are selected from the group consisting of: Computed Tomography (CT) images, Magnetic Resonance Imaging (MRI) images, and Positron Emission Tomography (PET) images.

18. The computer readable medium of claim 16, wherein the program instructions con- figured to establish a first reference coordinate system further comprises program instruc- tions configured to: define a first reference plane by three points each of which coincide with one of the anatomical landmarks of the plurality of external anatomical landmarks.

19. The computer readable medium of claim 18, wherein the three anatomical landmarks are the right external ear meatus, the left external ear meatus, and the bridge of the nose.

20. The computer readable medium of claim 18, further comprising program instructions configured to: adjust the reference plane by adding an offset delta to one of the three points.

21. The computer readable medium of claim 18, wherein the program instructions con- figured to translate the coordinates further comprise program instructions configured to: rotate the coordinates of the target about a first axis by the angle alpha; rotate the coordinates of the target about a second axis by the angle beta; and shift the coordinates of the target along a third axis by the particular distance.

22. The computer readable medium of claim 16, wherein the program instructions con- figured to establish a second reference coordinate system comprise program instructions configured to: select the origin of the second reference coordinate system as the external posi- tion.

23. The computer readable medium of claim 16, wherein the one or more angles com- prise: an angle theta that represents a rotation in an first plane of the second reference coordinate system; and an angle phi that represents an elevation in the first plane of the second reference coordinate system.

24. The computer readable medium of claim 16, wherein the target is inside the head of the patient and the external position is on the surface of the head of the patient.

25. The computer readable medium of claim 16, wherein the one or more images of the patient do not show a locator device attached to the patient and the program instructions configured to establish the first reference coordinate system operate without reference to a locator device attached to the patient.

26. A locator device for use in determining one or more angles at which to deliver radia- tion to a target inside of a patient, the locator device comprising: a head ring; a plurality of locators coupled to the head ring, each of the locators configured to be aligned with an external anatomical landmark of the patient, the external anatomical landmarks defining a first reference coordinate system in which coordinates of the target are known; a contact plate configured to be moved to an external position on the patient from which radiation is to be delivered; and io a plurality of guides that movably couple the contact plate to the head ring, the π plurality of guides including markings that indicate the position of the plate in relation to

12 the first reference coordinate system, the position providing information sufficient to

13 translate the coordinates of the target from the first reference coordinate system to a sec-

14 ond reference coordinate system whose origin is at the external position, and for determi- is nation of one or more angles from the external position to the target.

1 27. The locator device of claim 26, wherein the external anatomical landmarks comprise

2 the right external ear meatus, the left external ear meatus, and the bridge of the nose.

1 28. The locator device of claim 27, further comprising:

2 a rotating guide coupled to the head ring, the rotating guide adjustable by an angle

3 alpha in relation to the head ring;

4 a sliding guide coupled to the rotating guide, the sliding guide adjustable by an s angle beta in relation to the rotating guide; and

6 a movable rod coupled to the rotating guide and the contact plate, the movable rod

7 adjustable by a particular distance.

1 29. A treatment cap for delivering radiation to a target inside of a patient, the treatment

2 cap comprising:

3 a surface configured to fit around the head of a patient;

4 a unit located at a particular position and at a particular orientation in the surface, s the unit including,

6 a main body; and

7 a holder configured to hold a radiation source, the holder movably coupled a to the main body to permit rotation in a plane parallel to a base of the main body,

9 and to permit rotation in a plane normal to the base of the main body.

1 30. The treatment cap of claim 29, wherein the particular position and the particular ori-

2 entation in the surface are determined in relation to a plurality of external anatomical

3 landmarks on the patient.

RECTIFIED SHEET (RULE 91)

ISA/EP ^; 3i. The treatment cap of claim 29, wherein the main body comprises one or more protu- berances for contacting the head of the patient.

32. The treatment cap of claim 31 , wherein the one or more protuberances are contact pins.

33. The treatment cap of claim 29, wherein the radiation source is an ultrasound trans- ducer.

34, The treatment cap of claim 29, wherem the interface unit further comprises: a contact material disposed inside the main body, the contact material configured to contact the head of the patient, the contact material conductive of radiation from the radiation source.

35. The treatment cap of claim 34, wherein the interface unit further comprises: a sensor embedded in the contact material, the sensor configured to sense pressure fluctuations to measure intensity of radiation that is reflected from the patient.

36. The treatment cap of claim 29, further comprising: a second unit located a second particular position and at a second particular orien- tation in the surface, the second unit configured to also deliver radiation to the target

37. The treatment cap of claim 36, wherein the first unit and the second unit are interface units.

38. A device for delivering radiation to a target inside of a patient, the device compris- ing: a main body configured to be located at a particular position and at a particular orientation on the patient; and

RECTFfED SHEET (RULE S1) ISA/EP 5 a holder configured to hold a radiation source, the holder movably coupled to the

6 main body to permit rotation in a plane parallel to a base of the main body by a first an-

7 gle₃ and to permit rotation in a plane normal to the base of the main body by a second an-

8 gle, wherein the first and second angles are selected so that radiation delivered will inter-

9 cept the target inside of the patient.

1 39. The device of claim 38 wherein the particular position and the particular orientation

2 on the patient are determined in relation to a plurality of external anatomical landmarks

3 on the patient.

1 40, The device of claim 38, wherein the target is inside the head of the patient and the

2 particular position is on the surface of the head of the patient.

1 41. The device of claim 38, wherein the main body comprises one or more protuberances

2 for contacting the head of the patient

i 42. The device of claim 41 , wherein the one or more protuberances are contact pins,

i 43. The device of claim 38, wherein the radiation source is an ultrasound transducer,

1 44. The device of claim 38, further comprising:

2 a contact material disposed inside the main body, the contact material configured

3 to contact the head of the patient, the contact material conductive of radiation from the

4 radiation source.

i 45. The device of claim 38, wherein the interface unit further comprises: i a sensor embedded in the contact material, the sensor configured to sense pressure

3 fluctuations to measure intensity of radiation that is reflected from the patient.

RECTΪFΪED SHEET (RULE 91) fSA/EP

46. The device of claim 38, wherein the interface unit further comprises: a first indicia arranged upon the main body and configured to indicate the value of the first angle.

47. The device of claim 38, wherein the interface unit further comprises: a second indicia arranged upon the main body and configured to indicate the value of the second angle.

RECTIFIED SHEET (RULE 91) ISA/EP