More particularly, the present invention is directed to hyperthermia procedures where radiation is used to heat tumor cells to therapeutic temperatures which are lethal to the tumor cells.

2. Description of Related Art A wide variety of radiation therapy techniques and procedures have been developed for treating tumors. Radiation therapy may be used as a stand alone treatment or used in conjunction with surgery or chemotherapy. One of the principle problems associated with any therapy which utilizes radiation is controlling the radiation so that maximum damage to tumor cells is achieved with minimum damage to normal cells.

Hyperthermia is a tumor treatment procedure which involves heating tumor cells to therapeutic, i. e. lethal, temperatures. This procedure is based on the well-known medical fact that heating of body tissue to temperatures in excess of 65°C results in destruction of the cells. Microwave and radio frequency (RF) radiation have both been used as the source of energy in hyperthermia procedures. However, as with other radiation based procedures, a major problem has been limiting the build-up of heat to the tumor mass in order to prevent damage to surrounding normal cells. This problem is particularly troublesome when treating tumors located deep within the body or when treating brain tumors.

The majority of hyperthermia procedures have been directed to treating tumors which are located relatively close to the exterior of the body. These procedures have been relatively successful because the radiation must pass through a relatively small amount of healthy cells in order to reach the tumor mass. Hyperthermia procedures for treating tumors located deep within the body have been far more problematic. The collateral damage to healthy tissues

in the vicinity of the tumor or in the path of the radiation beam has been a serious drawback for both radiation therapy and hyperthermia of such deep tumors. The same problems have been experienced to an even greater degree with respect to brain tumors where damage to healthy brain cells surrounding the tumor must be kept to an absolute minimum.

Controlling the amount of collateral damage which occurs during radiation hyperthermia treatment of brain tumors and deep body tumors is particularly complicated because the various tissue and bone cells through which radiation must travel to reach the tumor absorb and transmit radiation at different levels. As a result, there is the potential for forming complex patterns of standing waves and hot spots in healthy tissues and other parts of the body.

This undesirable formation of standing waves and hot spots effectively prevents the use of sufficient radiation to elevate the tumor area to the temperatures required for total destruction of the tumor cells.

In view of the above, there is a continuing need to develop systems and procedures for treating tumors by hyperthermia where the tumors are located in the brain or deep within the body where collateral radiation/heat damage to healthy tissue is a problem.

SUMMARY OF THE INVENTION In accordance with the present invention, a system and procedures are provided for using radiation hyperthermia to selectively treat brain tumors and/or tumors located deep within the body. The system and procedures provides maximum heating of tumors while at the same time minimizing collateral damage to healthy cells.

In accordance with the present invention, a system is provided for applying a lethal dose of radiation to tumor cells located within a living mammal. The tumor cells which may be treated by this system are in the form of a tumor or other group of cells having an exterior boundary which defines the tumor body. The system is specifically designed to treat tumor bodies which are surrounded by non-tumorous cells. The system inclues a three- dimensional tumor imager that measures the tumor body and provides image data which accurately establishes the location of the tumor within the living mammal. At least two radiation sources are provided which are located exteriorly of the mammal. Each of the radiation sources is capable of producing

a well-defined beam of radiation. Beam directors associated with each of the radiation sources are provided to allow controllable pointing of the beams of radiation in desired directions. A final element of the treatment system is a radiation control center, which receives image data from the tumor imager, and uses this data to control the beam directors to provide focusing of the two or more beams of radiation on the tumor body. The radiation control center controls the intensity of radiation in each of the radiation beams, so that each individual beam is non-lethal to the non-tumorous cells, whereas the combined radiation intensities of the two or more beams of radiation focused on the tumor body are lethal to the tumor cells.

The present invention combines two principles to provide a single system which is especially well-suited for treating brain tumors and other tumors located deep within the body. The first aspect of the invention deals with accurate three-dimensional imaging of the tumor using any of the current imaging equipment such as CAT scan or magnetic resonance imaging. The three-dimensional boundary of the tumor is then digitized in the X, Y, Z axis with respect to reference points in the body, such as parts of spine joints and other bodily landmarks and the table upon which the patient is secured.

Depending on the physical structure of the imaging equipment and therapy apparatus, which may be designed as part of the imaging equipment, either the patient is moved along with the table or the imaging equipment is removed and replace with the therapy equipment.

Using the reference points, the therapy equipment is positioned so that stored digital information outlining the three-dimensional boundary of the tumor can generate commands for movement of the therapy apparatus by means of actuators through the X, Y, Z axis in the same manner as a (CNC) machine tool. As a result, the point of convergence or intersection of radiation beams or other modality can transcribe the space within the volume of the tumor point by point and plane by plane, at a speed which can effectively impart the necessary radiation dosage or temperature rise to the tumor, until the entire volume of the tumor and its boundary layer, as determined by the physician, has received and been treated by the radiation or other prescribed modality.

The second aspect of the invention involves the use of multiple sources of radiation or microwave electromagnetic emitters or electron beams or other modality in several planes and from different directions in a manner such that

all beams have a point of convergence at the tumor. For instance, in an annular phased array, microwave apertures or point of intersection of various x-ray emitters can form a defined and concentrated point at which all various emitters converge their beams or pass through.

In the case of microwaves, this invention also includes provisions for switching between various emitters so that the focal point in the case of phased array (or point of intersection in the case of multiple source emitters) is at all times receiving microwave energy from one or more sources while several of the sources are in the switched off position. This allows dissipation of heat by means of blood flow and conduction from the healthy tissues.

The above described and many other features and attendant advantages of the present invention will become better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an exemplary preferred system for applying a lethal dose of radiation to tumor cells in accordance with the present invention.

FIG. 2 is a view of FIG. 1 taken in the 2-2 plane.

FIG. 3 is a partial top view of FIG. 1 showing exemplary movement of the radiation sources.

FIG. 4 is a schematic representation of a general radiation control center or system which is designed to receive image data from the tumor imager and use this data to provide control of the beam directors in order to focus the radiation beams on the tumor body.

DETAILED DESCRIPTION OF THE INVENTION With the present invention, the patient is securely strapped down or otherwise secured on a non-metallic surface. An accurate three-dimensional image of the tumor using a magnetic resonance imaging (MRI) system or a CAT scan or such is obtained and digitized. The digitized information is then used to direct the travel of an annular device around the patient to which is attached

two or more sources of electromagnetic, ultrasound or other deep heat generating medium. The sources of radiation must be capable of providing a concentrated and narrow beam so that the point of intersection of the multiple beams is at or near the geometrical center of the annular structure. Means are provided for rotational travel of the annular structure around its geometrical center back and forth in predetermined arcs and speeds of rotation with means for adjustment depending on the procedure applied. Means are also provided for changing the angle of sources of energy so that the point of intersection of the beams can be moved away along a line at or close to the geometric center of the annular structure and perpendicular to its plane.

The annular structure is supported by an overall structure which can travel in the X, Y, Z axis by means of computer controlled actuators receiving movement signals from the computer fed with the three-dimensional digitized image data of the tumor.

As the energy sources are activated, the annular structure is given a circular movement around its geometric center and the geometric center of the annular structure which is also the center and point of intersection. The multiple sources are controlled to systematically move the beam intersection or focal point within the volume of the tumor to be treated at a pre-determined speed which is calculated to generate the desired temperature rise within the tumor. The calculations must take into account the intensity of the energy source, specific absorption rate (SAR) of the tissue and intensity of blood flow within the tissue.

In general, the rotational speed and travel arc of the annular structure around its geometrical center is calculated with respect to the absolute location of the tumor and with respect to the relative location of the tumor body with respect to the surrounding healthy skin, fat, tissue and bones in the path of heat generating radiation beams. In this way, the geometric center of the annular structure and therefore point of application of the multiple beams remains within the tumor at all times. At the same time, by applying rotational movements to the beam sources, the pathway of the beams through healthy body parts is varied. As a result, natural blood flow reduces any heat buildup in the momentary pathway of the beams. Since the beams are constantly changing their pathway, any momentary temperature rise is reduced before the healthy tissues are subjected to toxic levels of radiation.

The above-described general procedure is preferably carried out using a system of the type shown generally at 10 in FIGS. 1 and 2. The system 10 inclues a three-dimensional tumor imager, such as an MRI or CAT scan which is shown generically at 12. Although a CAT scan or MRI is preferred, any imaging system may be used which is capable of providing image data which establishes accurately the location of the tumor body 14 within the patient 16.

In a preferred embodiment of the present invention, three radiation sources 18, 20 and 22 are mounted to an annular ring 24. The radiation sources 18,20 and 22 are mounted to the annular ring 24 by way of beam directors 26,28 and 30, respectively. The beam directors 26,28 and 30 are preferably servo- actuated universal movement devices, which provide a movable universal mounting for each of the radiation sources to the annular ring 24. As best shown by the double-headed arrows in FIGS. 2 and 3, the beam directors 26, 28 and 30 allow movement of the radiation sources 18,20 and 22 in all three dimensions. The use of servomotor mountings to provide accurate three- dimensional positioning of attached radiation devices is well known. Any of the highly accurate servomounting systems may be utilized. The principal consideration is that the beam directors 26,28 and 30 include sufficient mounting hardware and servomotors to allow accurate focusing of the radiation beams on the tumor 14 as best shown in FIGS. 2 and 3, where the phantom lines traveling from the radiation sources 18,20 and 22 to the tumor body 14 are represented in phantom at 32.

In order to provide variable positioning of radiation sources 18,20 and 22, it is preferred that a rotational drive mechanism be provided which can rotate the radiation sources around the tumor as represented by double-headed arrow 34. As best shown in FIG. 2, a gear drive mechanism 36 and rollers 38 and 40 are provided for providing controlled rotation of the radiation sources 18,20 and 22 about the patient 16.

A radiation control center or system (shown as control panel 42) is provided for receiving image data from the MRI 12. The control center 42 is further designed to use this data to control the beam directors 26,28 and 30 to focus the radiation beams 32 onto the tumor body 14 as best shown in FIGS. 2 and 3. The control center 42 is designed also to provide control of the intensity of the radiation beams and rotation of annular ring 24, so that each individual beam is non-lethal to the non-tumorous cells whereas the combined

radiation intensities of the beams as they intersect or focus upon tumor body 14 combine to form a lethal temperature or radiation dose.

An exemplary control system is shown in FIG. 4 where the numerical designations to the various schematic boxes correspond to the numerical designations in FIGS. 1,2 and 3. The control system outlined in FIG. 4 is exemplary only, with it being understood that other control systems are possible provided that accurate feedback between the imaging system and radiation beam directors is provided so that accurate focusing of the radiation beams onto the tumor body is achieved.

In a preferred embodiment of the invention, the radiation sources 18,20 and 22 may be switched on and off in order to further limit the exposure of normal tissues to radiation.

The switching frequency can be adjusted from several seconds on or off for each source, to several cycles per second with further adjustments. For instance, if twenty emitters are used with five sources on and fifteen sources off at any given time, then each emitter has a duty cycle of 25%. This means that for each second of microwave energy exposure in a healthy tissue, there are three seconds during which the healthy tissue can be cooled by blood flow, while the tumor is receiving constant dosage from five sources, or twenty times the dosage of a healthy tissue without pause for cooling down.

Systematic switching of the sources have various benefits over the use of multiple sources without switching the sources in an on-and-off fashion. For example, on-and-off switching eliminates standing waves which otherwise form at the boundary of bones or fat and tissue which result in formation of hot spots regardless of how benign each source is. Furthermore, on-and-off switching allows natural heat conduction and blood flow to reduce any elevated temperatures at boundaries of various fat, tissue and bone formation.

Furthermore, by switching the microwave sources on and off based on the tumor temperature, energy output of microwave sources at the point of intersection of microwave beams, estimate of blood flow through the tumor and speed of traversing the intersection point of beams through the tumor, it is possible to calculate the temperature rise through the tumor within acceptable tolerances for effective destruction of tumor cells and without collateral damage to healthy tissues.

Switching is carried out by the electronic control center 42 which will turn the emitting sources systematically on and off and can be programmed for various exposure modes depending on the size and nature of the tumor and its location in the body as well as the nature of surrounding healthy tissues and bone structure.

Although the greatest benefit of on-and-off switching is in hyperthermia due to the relief afforded the healthy tissues to cool down and elimination of hot spots, the invention can readily be applied to x-ray and other radiation treatments as readily.

Having thus described exemplary embodiments of the present invention, it should be noted by those skilled in the art that the disclosures herein are exemplary only and that various other alternations, adaptations and modifications may be made within the scope of the present invention.

Accordingly, the present invention is not limited to the specific embodiments as illustrated herein.