EP1485019A2

EP1485019A2 - Method and apparatus for image-guided radiotherapy

Info

Publication number: EP1485019A2
Application number: EP01966596A
Authority: EP
Inventors: Euan Thomson; Alan P. Sliski
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 2000-09-07
Filing date: 2001-09-06
Publication date: 2004-12-15
Also published as: WO2002020084A2; AU2001287097A1; EP1485019A4; WO2002020084A3

Abstract

An apparatus for delivering therapeutic radiation to a treatment region in a body in accordance with a prescribed dose distribution includes a source of therapeutic radiation (14), and an image-guided surgery system (12). The image-guided surgery system includes a position tracking system (16) for tracking a position of the source with respect to the treatment region, and an imaging system (24) for generating visual images (100) in response to input data. A method is disclosed for delivering a prescribed dose of therapeutic radiation to a treatment region having an arbitrary geometry. A visual image representing a prescribed dose distribution (100) within the treatment region is generated. Therapeutic radiation is delivered to the treatment region, and a cumulative dose of the radiation actually delivered to desired points within the treatment region is calculated. A visual image (100) representing the delivered cumulative dose of radiation is generated and displayed. The amount of therapeutic radiation delivered to the treatment region is adjusted so that the delivered dose substantially matches the prescribed dose distribution at any desired point within the treatment region.

Description

METHOD AND APPARATUS FOR IMAGE-GUIDED RADIOTHERAPY

Cross-Reference to Related Applications

This application claims the benefit of priority from U.S. Application Serial No.

09/656,878 entitled METHOD AND APPARATUS FOR IMAGE-GUIDED RADIOTHERAPY, filed September 7, 2000, incorporated herein by reference.

Field of the Invention The present invention relates generally to radiotherapy, and more particularly to method and apparatus for delivering a prescribed dose of radiation to a treatment region having an arbitrary geometry.

Background of the Invention In the field of medicine, radiation is used for diagnostic, therapeutic and palliative treatment of patients. When using radiation to treat cancer, a surgeon typically directs radiation to remove a tumor and as much surrounding tissue containing cancer cells as possible, without damaging critical structures. In many cases, tissue that contains cancer cells is left in the tumor site, for various reasons including inability to remove the tissue. In these cases, the tumor is likely to recur from the remaining tumor cells.

It is therefore desirable to give a radiation treatment to the margins of a tumor resection site, in order to reduce the likelihood that cancer may recur due to tumor cells that have not been excised. Radiation treatment after removal of a tumor is generally referred to as intraoperative radiation therapy. The conventional medical radiation sources used for these treatments include large fixed position machines such as linear accelerators ("LINACs"), and smaller transportable radiation delivery machines. Conventional radiation treatment systems, such as the LINACs, utilize a high power remote radiation source and direct a beam of radiation at a target area, such as tumors inside the body of a patient. This type of treatment is referred to as teletherapy because the radiation source is located at a predefined distance, typically about one meter, from the target. A disadvantage of teletherapy is that tissue disposed between the radiation source and the target is exposed to radiation.

An alternative treatment system utilizing a point source of x-ray radiation is disclosed in U.S. Patent No. 5,153,900 issued to Nomikos et al., U.S. Patent No. 5,369,679 to Sliski et al, U.S. Patent No. 5,422,926 to Smith et al, and U.S. Pat. No. 5,621,780 to Smith et al, which are all owned by the assignee of the present application, and are all hereby incorporated by reference. The system includes a miniaturized,' insertable probe adapted for producing a low power dose of radiation at a distal end of the probe. X-rays are emitted from a nominal point source located within or adjacent to the desired area to be affected. This type of treatment, in which the source is located close to or within the area receiving treatment, is referred to as brachytherapy. One advantage of brachytherapy is that the radiation is applied primarily to treat a predefined tissue volume, without significantly affecting the tissue in adjacent volumes.

All of the above-referenced techniques use fixed, predefined dose geometries to ensure that the dose delivery is predictable. For example, U.S. Pat. No. 5,621,780 discloses an apparatus and method for irradiating a surface defining a body cavity, in accordance with a predetermined dose distribution. The surface is conformed to a predetermined contour, such as a sphere, and the source of radiation is then adjusted to establish a uniform dose at that surface. During surgical removal procedures, however, treatment regions having arbitrary and irregular geometries are often encountered. It is desirable to deliver a prescribed dose of radiation to such arbitrarily and irregularly shaped regions. It is therefore an object of this invention to provide a method and apparatus for delivering a prescribed dose of radiation to a treatment region having an arbitrary and irregular geometry.

Summary of the Invention

The present invention relates to a method and apparatus for delivering a prescribed dose of therapeutic radiation to a treatment region having an arbitrary or irregular geometry. The apparatus includes a source of a therapeutic radiation, and an image-guided surgery system. The image-guided surgery system includes a position tracking system for tracking a position of the source with respect to the treatment region, and an imaging system for generating visual images in response to input signals and data. The apparatus further includes a display mechanism such as a display screen for displaying visual images.

The therapeutic radiation may include x-ray radiation, γ-ray radiation, electron radiation, laser radiation, ion radiation, electromagnetic radiation, ultrasonic radiation, thermal radiation, infrared radiation, and ultraviolet radiation. In one embodiment, the source of therapeutic radiation is an x-ray source that includes a housing, and an elongated probe extending therefrom. The probe is insertable within the treatment region, and produces a dose of radiation at a distal end of the probe.

The position tracking system may include a tracking device for generating signals representing the position of the source, and one or more receivers for receiving the signals. In one embodiment, the receivers may be cameras. In one embodiment, the tracking device includes an array of emitters. In one embodiment, the emitters are light emitting diodes (LEDs) or infrared emitting diodes (IREDs). A processor within the image-guided surgery system determines the position of the source within the treatment region, in response to the images captured by the receivers. The imaging system includes a digital processor which generates visual images in response to input signals and data. The imaging system generates a visual image of the treatment region prior to treatment, and if desired, during treatment. In response to position information from the position tracking system, the imaging system generates -a visual image of the position of the source within the treatment region. In response to input prescription data, the imaging system generates a visual image of a prescribed dose distribution of the therapeutic radiation within the treatment region. The imaging system also generates in real time a visual image of a cumulative dose of the therapeutic radiation that is delivered during the treatment.

A method is disclosed for delivering a prescribed dose of a therapeutic radiation to a treatment region within an anatomical structure. A visual image of the treatment region is generated. An appropriate dose of the therapeutic radiation is prescribed for all desired points within the treatment region. A visual image of a prescribed dose distribution within the treatment region is generated, and may be superposed upon the previously generated visual image of the treatment region.

The therapeutic radiation is then delivered to the treatment region, for example by turning on a source of radiation. As the source is moved within the treatment region to deliver the radiation, a visual image representing the position of the source within the treatment region is generated. During delivery of the therapeutic radiation, a cumulative dose of the radiation actually delivered by the source to any desired point within the treatment region is calculated. A visual image representing the delivered cumulative dose is generated, and the visual image is displayed on a screen. The surgeon adjusts the amount of therapeutic radiation delivered to the treatment region, so that the delivered dose substantially matches the prescribed dose distribution at any desired point within the treatment region.

Brief Description of the Drawings FIG. 1 illustrates one embodiment of an apparatus in accordance with the present invention for delivering a prescribed dose of therapeutic radiation to a treatment region in a body.

FIG. 2 (a) is a perspective view of a miniature x-ray source for use in image-guided radiotherapy. FIG. 2 (b) is a more detailed illustration of the components of the x-ray source. FIG. 3 shows the x-ray source integrated with an image-guided surgery system.

Detailed Description FIG. 1 is a perspective view of one embodiment of an apparatus 10 in accordance with the present invention for delivering a prescribed dose of therapeutic radiation to a treatment region in a body. The treatment region may be a superficial tumor bed after the removal of a tumor, or a cavity within the body from which the tumor has been surgically resected. The treatment region may have an arbitrarily and irregularly shaped geometry. In overview, the apparatus 10 includes an image-guided surgery system 12, and a source

14 of therapeutic radiation that can be integrated with the system 12. The source 14 may be a miniaturized x-ray source, as described in detail below. The image-guided surgery system 12 includes a position tracking system 16, and an imaging system 24. The position tracking system 16 measures and tracks the position of the source 14 with respect to the treatment region, as the surgeon moves the source 14 within the treatment region. Using the position information received from the position tracking system 16, the imaging system 24 generates a visual image 100 representing the cumulative dose of radiation delivered by the source 14 to each point within the treatment region. The visual image 100 is displayed on a display mechanism 28, such as a monitor display screen 28, to guide the surgeon during his delivery of therapeutic radiation. The imaging system 24 may be located within a separate workstation 31 , as illustrated in FIG. 1. In one embodiment, the position tracking system 16 includes a tracking device 18 mounted on the source 14, and one or more receivers 20 which observe the source 14. In one embodiment, the receivers 20 are cameras. The position tracking system 16 is connected to a processor 17 within the image-guided surgery system 12. The processor 17 may be located within the workstation 31. The tracking device 18 may include emitters 19 attached to the source 14 for tracking the position and movement of the source 14. For example, two or more emitters 19 may be mounted on a tubular probe 40 of an x-ray source 14, including on the tip of the probe 40. The emitters 19 generate a signal representing the position and movement of the source 14. Preferably the emitters 19 are light emitting diodes (LEDs) or infrared emitting diodes (IREDs); however, other tracking devices known in the art capable of being tracked by corresponding sensors are within the scope of this invention. For example, the tracking device 18 may be a device capable of generating active signals, including, but not limited to, acoustic, electromagnetic, and radar signals. Optical sensing is generally preferred over other methods such as acoustic or electromagnetic field sensing, which are more sensitive to environmental effects compared to optical sensing. The cameras 20 detect the signals emitted by the emitters 19. From the signals supplied by the cameras 20, the processor 17 determines the position of the source 14 relative to the treatment region.

The imaging system 24 has a digital processor 25, which is coupled to the cameras 20 by suitable communication means. The digital processor 25 converts the images captured by the cameras 20 into digital form, and stores them in a memory unit 26 within the imaging system 24. The imaging system 24 has sufficient memory storage capacity for a number of digitized images. Preferably the imaging system 24 also includes a hard copy capability for producing a hard-copy image from the stored images. Referring to FIG.s 2(a) and 2(b), the source of therapeutic radiation is a miniaturized x- ray source 14 that delivers radiation directly to the tumor site. FIG.s 2(a) and 2(b) illustrate exemplary systems that utilize an x-ray source as a source of therapeutic radiation. It is within the scope of the present invention, however, to use other sources of therapeutic radiation, such as sources of γ-ray radiation, electron radiation, laser radiation, ion radiation, electromagnetic radiation, ultrasonic radiation, thermal radiation, infrared radiation, and ultraviolet radiation. In the embodiment illustrated in FIG.s 2(a) and 2(b), the x-rays are emitted from a small, well- defined source 14 located within or adjacent to the treatment region. A suitable x-ray source is described in detail in U.S. Pat. No. 5,153,900, referenced above. FIG. 2(a) provides a perspective view of one embodiment of a miniature x-ray source 14 as described in U.S. Pat. No. 5,153,900 and suitable for use in the present invention. FIG. 2(b) provides a more detailed illustration of the x-ray source 14. Typically, the x-ray source 14 operates in the range of about 10 kV to about 90 kV, and electron beam currents in the range of approximately 1 μA to 100 μA. Adequate tissue penetration and cumulative dosage may be attained by locating the x-ray source adjacent to or within the region to be irradiated. The x-ray source 14 includes a housing 29 and an elongated tubular probe 40 extending from the housing 29 along a reference axis 41, and a target assembly 46 at the distal end of the probe 40. The housing 29 encloses an electron beam source, and includes elements for generating an electron beam along a beam path. The tubular probe 40 extends along the reference axis 41 from the housing 29 about the beam path. The target assembly 46 includes a target element 47 positioned in the beam path. The target element 47 is adapted to emit x-rays in response to electrons incident thereon from the beam. The x-ray source 14 may be used in a manner where only the probe 40 is inserted into a patient while the housing 29 remains outside the patient.

The housing 29 encloses a high voltage power supply 29-a. The probe includes an electron beam generator (cathode) 42 positioned adjacent to the power supply 29-a. The high voltage power supply 29-a establishes an acceleration potential difference between the cathode 42 and a grounded annular anode 43, so that a thin electron beam (typically 1 mm or less in diameter) is established within the probe 40 along the reference axis 41, through the center of the anode 43 to the target assembly 46. The power supply 29-a may be programmable, so that the voltage, current, and duration of the electron beam source may be varied as desired.

The target element 47 is an x-ray emission element 48. In one embodiment, the x-ray emission element 48 consists of a small beryllium (Be) window coated on the side exposed to the incident electron beam with a thin film of a high-Z element such as gold (Au), tungsten (W), or uranium (U). The incident electrons generally cause the target element 47 to act as a point source of x-rays. The accelerated electrons interact with the target material, converting part of their energy into electromagnetic radiation. The emitted x-ray spectrum is composed in part of discrete energies characteristic of transitions between bound electron energy levels of the target element 47, and an x-ray energy continuum known as bremsstrahlung. Bremsstrahlung is caused by acceleration of the beam electrons as they pass near target nuclei.

The x-rays emitted from the target assembly 46 are introduced into the malignant cells in the treatment region, for selective destruction of the cells. The x-ray emission element 48 of the target assembly 46 is adapted to be adjacent to or within the region of a patient to be irradiated. The proximity of the emission element 48 to the treatment region eliminates the need for high voltages (used in prior art machines) to achieve satisfactory x-ray penetration through the body wall. The low voltage of the x-rays also concentrates the radiation in the targeted tissue, and limits the damage to surrounding tissue and surface skin at the point of entry.

The x-ray source 14 may include an internal radiation monitor (IRM) 50 which provides a real time measurement of the radiation output from the x-ray source. The IRM uses a radiation detector that is internal to the x-ray source 14, and detects the radiation that passes back along the path of the electron beam. The IRM 50 monitors the delivery of radiation dose to the patient. The signal from the IRM 50 is calibrated to the dose rate before the probe 40 is placed in the patient for treatment. The integrated IRM output is used during treatment as a direct measure of the delivered radiation dose. FIG. 3 shows the x-ray source 14 as integrated with the image-guided surgery system 12.

As explained in conjunction with FIG.s 2(a) and 2(b), FIG. 3 illustrates an exemplary embodiment in which an x-ray source 14 is integrated with the image-guided surgery system 12, however it is within the scope of the present invention to integrate other sources of therapeutic radiation, such as sources of γ-ray radiation, electron radiation, laser radiation, ion radiation, electromagnetic radiation, ultrasonic radiation, thermal radiation, infrared radiation, and ultraviolet radiation, with the image-guided surgery system 12. The probe 40 of the source 14 is moved within the treatment region as the surgeon delivers the therapeutic radiation. Emitters 19 are shown mounted on the probe 40. The cameras 20 detect the signals emitted by the emitters 19, as the probe 40 is moved.

In operation, the patient is placed on an operating table, which preferably is in proximity to the display screen 28 used by a surgeon or radiation oncologist. The surgeon defines a treatment region within an anatomical structure of the patient. Typically, the treatment region is a tumor resection site, and has an irregular geometry. A visual image 32 of the treatment region is generated prior to or during surgery. The visual image 32 may be generated by mapping a geometry of the treatment region using a tactile probe. A three dimensional model of the mapped treahnent region may be generated, and stored within the memory unit 26 of the processor 25 for later retrieval. The visual image 32 may include, but are not limited to, CT (computer tomography) or MRI (magnetic resonance imaging) images. If desired, image information can be acquired again during the surgical procedure, i.e. new CT images or MRI images can be generated during surgery.

The visual image 32 of the treatment region is displayed on the display mechanism 28 for the surgeon. By viewing the tumor resection site through the visual image 32, the surgeon prescribes a medically appropriate dose of therapeutic radiation for any desired point within the irregularly shaped treatment region. For example, if the treahnent region is a tumor resection site, the surgeon can prescribe for each desired area within the site a dose of radiation that he deems is necessary to prevent recurrence of cancer. A dose prescribed by the surgeon can be input into a processor for any desired point within the treatment region, thus generating a prescribed dose distribution for the treatment region. The processor 17 is thereby loaded with a mathematical model of the prescribed dose distribution. The mathematical model outputs a prescribed dosage for any desired coordinate point within the treatment region.

The imaging system 24 generates a visual image 34 that represents the prescribed dose distribution within the treatment region. The image 34 of the prescribed dose distribution may be formed as a graphically superposed image over the previously obtained image 32 of the treatment region. The visual image 34 guides the surgeon during the surgical procedure, so that he may deliver radiation to any desired area within the irregularly shaped treatment region according to the prescribed dose distribution.

The surgeon turns on the x-ray source 14 to deliver the x-ray radiation to the treatment region. As the source 14 is moved within the treatment region, the position of the source 14 is tracked by the position tracking system 16. The cameras 20 preferably observe the source 14 from different directions. Preferably, multiple cameras 20 are used to triangulate the 3- dimensional location of the emitters 19 included in a tracking device 18 used in one embodiment of the present invention. The emitters 19 may be flashing LEDs or IREDs that are mounted on the source. As explained earlier, other tracking devices known in the art, such as devices capable of generating acoustic, electromagnetic, and radar signals, by way of example, may be used within the scope of this invention. A direct line-of-sight is preferably maintained from the cameras 20 to the emitters 19. The cameras 20 detect the signals from the emitters 19, and transmits the signals to the processor 17, which determines the position of the source 14 relative to the treatment region.

Processor 17 derives a corresponding position of the source 14 in the prerecorded CT or MRI image 32 of the treatment region. In one embodiment, fiducial marks are used for such a derivation. A plurality of fiducial marks provided on the treatment region, and are reproduced in the CT or MRI image 32. The processor 17 computes the positions of the marks on the treatment region, as well as the corresponding positions of the images of the marks in the image 32 of the treatment region. On the basis of the positions of the marks on the treatment region, and on the basis of the positions of the images of the marks in the image 32, the processor 17 derives a coordinate transformation which transforms arbitrary positions in the treatment region into corresponding positions in the image 32 of the treatment region. The imaging system 24 fetches from memory the CT or MRI image 32, and combines it with the position of the source 14 in the image 32, as calculated by the processor 17. Using the transformed position data, the imaging system 24 generates a visual image representing the position of the source 14 within the CT or MRI image 32 of the treatment region. The display screen 28 displays the position of the source 14 within the treatment region. For example, the position of the source 14 as the source 14 is moved by the surgeon may be represented by a blinking cursor. The surgeon can thus see the position of the probe 40 within the treatment region in the image on the screen, without him seeing the probe 40 directly.

As the surgeon moves the source 14 within the treatment region to deliver x-ray radiation to the treatment region, the IRM 50 in the source 14 calculates in real time a cumulative dose of radiation actually delivered by the source 14 to any desired point within the treatment region. The calculated cumulative dose information is sent to the imaging system 24. The imaging system 24 generates in real time a visual image 100 representing the cumulative dose of radiation delivered by the source 14 to each point within the treahnent region.

The visual image 100 of the cumulative dose delivered to the treatment region is displayed in real time on the display screen 28. The cumulative dose delivered to any point in the treatment region can thus be visualized by the surgeon while he is delivering the radiation treatment, and the visual image 100 serves as a guide to the surgeon. Visual display of the cumulative dose enables the surgeon to manipulate the source 14 so as to deliver the dose of radiation according to the prescribed dose distribution.

Referring to visual image 34 as indicative of the prescribed dose of radiation that should be delivered to each point within the treatment region, and using visual image 100 to keep track of the amount of radiation he is actually delivering, the surgeon adjusts the amount of x-ray radiation delivered to the treatment region so that the delivered dose substantially matches the prescribed dose distribution at any point within the treatment region. For example, the surgeon may move the x-ray source 14 away from areas within the treatment region in which the prescribed dose has been fully delivered, and move the source 14 toward areas within the treatment region that have received less than the prescribed dose. By using the programmable power supply 29-a of the x-ray source 14, the surgeon can control the amount of x-ray radiation being delivered to a particular point within the treatment region.

In one embodiment, different colors are used to represent the different cumulative doses at each point within the region. Areas that have received less than the prescribed dose may be displayed in a predetermined color, directing the surgeon to move the x-ray source 14 near the areas with less dose. The color-coded visual image 100 thus guides the surgeon to "paint" or "fill" any area within the treatment region so as to attain the desired dose distribution as displayed through color-coding. By viewing the visual images 34 and 100 in real time, the surgeon can manipulate the x-ray source 14 to attain the desired dose distribution, without needing to do any detailed preplanning. At the completion of the radiation treatment, the processor 17 can generate an output recording the dose delivered to the treatment region. The output can be made part of the surgical record of the patient.

In another embodiment, the method of the present invention can be adapted for an automated delivery system. In this embodiment, delivery of radiation can be pre-planned for delivery by a robotic system according to a prescribed dose distribution that is input into a processor within the robotic system. In this embodiment, the image-guided surgery system 12 serves as a quality assurance tool for verifying the dose distribution as it is delivered.

While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. An apparatus for delivering therapeutic radiation to a treatment region in a body in. accordance with a prescribed dose distribution, the apparatus comprising: (a) a source of therapeutic radiation; and (b) an image-guided surgery system, comprising (i) a position tracking system for tracking a position of said source with respect to the treatment region; (ii) a processor, responsive to said position tracking system, for calculating in real time a cumulative dose of the radiation actually delivered by the source to at least some points within the treatment region; and (iii) an imaging system for generating in real time a visual image representing said cumulative dose of radiation actually delivered to each of said at least some points within the treatment region.

2. An apparatus according to claim 1, further comprising a display mechanism for displaying in real time said visual image representing said cumulative dose of radiation actually delivered to each of said at least some points within the treatment region.

3. An apparatus according to claim 1, wherein said position tracking system comprises: (a) a tracking device mounted on said source, said tracking device generating signals representing the position of the source relative to the treatment region; and (b) at least one receiver for receiving said signals.

4. An apparatus according to claim 3, wherein said receiver comprises a camera.

5. An apparatus according to claim 3, wherein said tracking device comprises an array of emitters selected from the group consisting of light emitting diodes (LEDs) and infrared emitting diodes (IREDs).

6. An apparatus according to claim 1, wherein said therapeutic radiation is selected from the group consisting of x-ray radiation, γ-ray radiation, electron radiation, laser radiation, ion radiation, electromagnetic radiation, ultrasonic radiation, thermal radiation, infrared radiation, and ultraviolet radiation.

7. An apparatus according to claim 1, wherein said source of therapeutic radiation includes a housing having an elongated probe extending from said housing, and said probe is adapted for producing a dose of radiation at a distal end of said probe.

8. An apparatus according to claim 2 wherein said display mechanism includes a monitor screen.

9. An apparatus for delivering therapeutic radiation to a treatment region in a body in accordance with a prescribed dose distribution, the apparatus comprising: (a) a source of therapeutic radiation; (b) a position tracking system for tracking a position of said source with respect to the treatment region; (c) a processor, responsive to said position tracking system, for calculating in real time a cumulative dose of the radiation actually delivered by the source to at least some points within the treatment region; (d) an imaging system for generating visual images corresponding to the treatment region and the prescribed dose distribution within the treatment region, and for generating in real time a visual image representing said cumulative dose of radiation actually delivered to each of said at least some points within the treatment region; and (e) a mechanism for displaying the visual image of the prescribed dose distribution within the treatment region, and for displaying in real time the visual image representing said cumulative dose of radiation actually delivered to each of said at least some points within the treatment region.

10. A method for delivering a prescribed dose of a therapeutic radiation to a treatment region within an anatomical structure, the method comprising: (a) generating a visual image of the treatment region; (b) prescribing an appropriate dose of the therapeutic radiation for at least some points within the treahnent region; (c) generating upon said visual image of the treahnent region another visual image representing a prescribed dose distribution within the treatment region; (d) delivering at least some therapeutic radiation to the treatment region; (e) displaying in real time a visual image representing a cumulative dose of the therapeutic radiation actually delivered to each of said at least some points within the treatment region; and (f) adjusting an amount of therapeutic radiation delivered to the treatment region so that the delivered dose substantially matches said prescribed dose distribution at each of said at least some points within the treatment region.

11. The method of claim 10 wherein said therapeutic radiation is selected from the group consisting of x-ray radiation, γ-ray radiation, electron radiation, laser radiation, ion radiation, electromagnetic radiation, ultrasonic radiation, thermal radiation, infrared radiation, and ultraviolet radiation.

12. The method of claim 10 further including the step of defining the treatment region by sl ielding from radiation selected portions within the anatomical structure.

13. The method of claim 10 wherein the step of generating a visual image of the treahnent region comprises the steps of mapping a geometry of the treatment region, and creating a three- dimensional computerized model of the mapped treatment region.

14. The method of claim 10 wherein the step of displaying in real time a visual image representing a cumulative dose actually delivered to at least some points within the treatment region comprises the step of calculating a cumulative dose actually delivered to at least some points within the treatment region.

15. The method of claim 10 wherein the step of generating a visual image representing a prescribed dose distribution within the treatment region comprises the step of using a plurality of colors to represent an associated plurality of prescribed doses.

16. The method of claim 10 wherein the step of displaying in real time a visual image representing a cumulative dose delivered to each point within the treatment region comprises the step of using a plurality of colors to represent an associated plurality of cumulative doses.

17. A method for delivering a prescribed dose of therapeutic radiation to an anatomical structure having an arbitrary geometry, the method comprising: (a) mapping the geometry of the anatomical structure with a tactile probe to create a three-dimensional computer model of the anatomical structure; ) defining a treatment region within said three-dimensional model;

(c) generating a visual image of said treatment region;

(d) prescribing an appropriate dose of therapeutic radiation for at least some points within said treatment region;

(e) creating a visual image of a spatial distribution of the prescribed dose at each of said at least some points within said treatment region;

CD activating a source of therapeutic radiation and delivering at least some radiation to said treatment region;

(g) calculating a cumulative dose delivered to each of said at least some points within said treatment region;

GO generating and displaying in real time a visual image representing said cumulative dose delivered to each point within the region;

(i) operating the source of radiation so as to deliver to each point within the treatment region a dose of radiation that matches said prescribed dose distribution at each point within the treatment region.