System and Method for Multiple Particle Therapy

1. Field of the Invention

The present invention relates to a system for particle beam therapy and, in particular, concerns a system for producing a beam comprising multiple types of particles, including protons and neutrons, which are delivered to a target isocenter within the patient to be treated.

2. Description of the Related Art

Radiation therapy is used to treat, among other things, various forms of cancer. In particular, radiation therapy is often used to treat tumors and cancerous tissues within the body of a patient. Generally, radiation therapy involves directing a beam of sub-atomic particles at a region within the body of the patient containing the cancerous tissue. Ideally, when the sub-atomic particles contact the cancerous tissue, the energy of the sub-atomic particles destroys these cells or prevents these cells from reproducing or growing. Various types of sub-atomic particles are used in various forms of radiation therapy including, photons (X-rays), neutrons and protons. Each form of particle therapy has certain advantages and disadvantages.

For example, neutrons have a comparatively high Radio Biologic Effect (RBE), which is an empirically measured value indicative of the amount of damage to cells that is caused by the particle. Hence, neutrons can be very effective in destroying or damaging cancerous cells. However, it is generally very difficult to control a neutron beam so as to direct neutrons from a remote source into particular localized regions of a patient's body. Further, as neutrons travel through the body, they release energy at a generally constant rate along their path of travel. Neutrons deposit energy along their path and are also slowed significantly as a result of penetrating tissue. Neutrons have the unfortunate tendency to damage healthy tissue surrounding the tissue of interest, i.e., healthy tissue along the path of travel of the neutrons. Additionally, neutrons present a particular safety hazard in that they can penetrate deeply into almost any type of material including steel and concrete. Thus, if large quantities of neutrons are generated, radiation shielding becomes a significant problem.

In contrast, protons generally have a lower RBE. However, they are easier to control and exhibit a characteristic known as the Bragg peak whereby the energy released by a proton penetrating tissue rapidly increases when the proton slows to a threshold level. Consequently, by controlling the energy of the protons so that they slow down at the proper time, it is possible to cause most of their energy to be released in the proximity of the region of the cancerous cells. Protons are, therefore, very effective in destroying cancerous cells within the body of a patient while minimizing damage to surrounding cells.

While proton therapy can be very effective in some circumstances, there are sometimes cases where the RBE of a beam of protons may be insufficient to destroy the cancerous cells within a particular region. In these cases, proton radiation therapy is typically discontinued in favor of other therapies.

The beam therapy system of the present invention comprises a radiation therapy apparatus which produces beams comprised of two different sub-atomic particles, preferably protons and neutrons. The radiation therapy apparatus is particularly advantageous for treatment of conditions that are unresponsive to proton therapy alone.

In the preferred embodiment, the apparatus comprises a proton beam therapy system and a neutron generator which generates neutrons in response to bombardment by protons. In operation, a proton beam, produced by the proton beam therapy system, is directed toward a target isocenter which is proximate a region of malignant cells. A piece of neutron-rich material, such as Beryllium, is positioned in the path of the proton beam so that at least a portion of the protons collide with atoms within the material and produce neutrons that propagate in the general direction of the path of the proton beam. The apparatus produces a multiple particle beam containing both protons and neutrons which propagates towards the target isocenter in the patient's body. Malignant cells located proximate the target isocenter can thus be bombarded with neutrons alone, protons alone, or both neutrons and protons.

In one embodiment, the plate of a neutron-rich material is interposed between the nozzle of the proton beam therapy system and the patient. As the proton beam passes through the plate, some of the protons collide with atoms in the plate, resulting in the production of neutrons. The nature of the collision causes most of the neutrons to be propelled in the general direction of the proton beam towards the target isocenter in the patient's body.

As is generally understood, the Radio Biologic Effect (RBE) of the neutrons is significantly higher than the Radio Biologic Effect (RBE) of the protons. Hence, the overall effectiveness of the multiple particle beam in damaging the malignant cells can be greater than the overall effectiveness of the proton beam alone.

The number of neutrons that are created by the proton beam passing through the neutron-rich material is dependent, in part, upon the type and thickness of the material. Hence, in one embodiment, plates of different thicknesses can be positioned in an arm that is attached to the nozzle of the proton beam system. In another embodiment, the plate of the neutron-rich material has a varying type or thickness so that the number of neutrons created by the proton beam can be varied by having the proton beam either impinge on different positions on the plate or on different types of plates.

The neutrons emerge from the neutron-rich material with a generally Gaussian distribution. Although the neutrons propagate in the general direction of the proton beam, the neutrons emerging from the neutron-rich plate are not well collimated and, in this sense, there is some beam "spread". Since the neutrons can damage healthy tissue as well as the cancerous or tumorous tissue at the target isocenter, the neutron-rich material is preferably positioned as close to the patient's body as possible to minimize the effect of the beam spread caused by the neutron generation. Preferably, the neutrons represent a small percent of the total radiation dose that is delivered to the patient using the multiple beam therapy system. This relatively low proportion of neutrons to protons further minimizes the collateral damage to the healthy tissue surrounding the target isocenter.

Hence, the preferred embodiment provides a system which can simultaneously or sequentially deliver two different types of particles to a target isocenter within a patient's body thereby producing a heightened Radio Biologic Effect. Implementation can be accomplished inexpensively by modifying an existing proton beam therapy system, i.e., by adding a piece of neutron-rich material in the path of the proton beam.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings.

FIG. 1 is a perspective view of a particle beam therapy system of the preferred embodiment; and

FIG. 2 is a partial schematic view of a treatment station of the particle beam therapy system of the preferred embodiment illustrating the nozzle of a proton beam therapy system with a plate of neutron-rich material for producing neutrons.

Reference will now be made to the drawings wherein like numerals refer to like parts throughout. FIG. 1 illustrates a multiple particle beam therapy system 100 which comprises a proton beam therapy system 102 and a neutron source 104. The proton beam therapy system 102 comprises a proton source 110 connected to an accelerator 112 by an injector 114. The accelerator 112 accelerates the protons in a beam to a desired energy level and, via a beam transport system 116, delivers the proton beam to a patient supported in a fixed position at a treatment station 118. The proton beam therapy system 102 is under operator control via a computer control system (not shown).

At the treatment station 118, a gantry 128 which is rotatable about an axis of rotation supports a patient 142. The beam transport system 116 comprises a nozzle 150 which directs the protons towards a specific target isocenter within the body of a patient. While FIG. 1 illustrates only a single treatment station 118, it can be appreciated that the proton beam therapy system could comprise multiple treatment stations, each having a gantry rotatable about an axis. One embodiment of the proton beam therapy system 102 is more fully described in U.S. Pat. No. 4,870,287 which is hereby incorporated herein by reference.

As is well known in the art, protons are accelerated to a desired energy level in the accelerator 112, which in this preferred embodiment, is comprised of a synchrotron. Magnets are then used to extract the accelerated protons into the beam transport system 116. Switching magnets are used to direct the proton beam through the beam transport system 116 to the treatment station 118 wherein the patient 142 is positioned on a treatment platform 134. The energy level of the protons is preferably selected so that, when the proton beam is directed towards a target isocenter within the patient's body, the Bragg peak of the protons comprising the beam occurs within the region of the target isocenter to maximize the amount of energy delivered to the cells at the target isocenter.

As is understood in the art of proton beam therapy, it is important to deliver the proton beam accurately to the target isocenter. Further, proton beam therapy is generally enhanced when the proton beam can be delivered from a variety of different angles. Hence, it is generally desirable to place the patient 142 in a fixed position relative the nozzle of the beam delivery system 102 and to move the nozzle to various positions via the movable gantry 128 such that the beam is delivered from a variety of different angles. U.S. Pat. No. 4,905,267 and U.S. Pat. No. 5,117,829 each disclose systems for aligning a patient for radiation treatment and each of these references are hereby incorporated herein by reference. Further, U.S. Pat. No. 4,917,334 and U.S. Pat. No. 5,039,057 each disclose a gantry system which allows for delivery of a radiation beam over a continuous range of different angles and each of these patents are hereby incorporated herein by reference. Further, various other methods of selecting treatment for patients, apparatuses for enhancing the delivery of radiation beams to patients, and the like, are disclosed in U.S. Pat. Nos. 5,017,789, 5,240,218 and 5,260,581 which are also hereby incorporated herein by reference.

FIG. 2 is a schematic illustration of a nozzle 150 of the proton beam therapy system 102 with an attached neutron source 104. In this embodiment, the neutron source 104 is comprised of a piece of neutron-rich material 154 that is coupled to a bracket 160 that is, in turn, mounted on the nozzle 150 so that the neutron-rich material 154 is positioned in the path of a proton beam 161 produced by the proton beam therapy system 102. The neutron source 104 can be positioned in the path of the proton beam 161 to produce neutrons or can alternatively be removed from the path of the proton beam 161 so that the patient only receives protons. Further, the neutron source 104 can be alternatively positioned within and removed from the path of the proton beam 161 so that the patient sequentially receives doses of protons and doses of neutrons as part of a treatment program. When a proton beam 161 impinges upon the neutron-rich material 154, at least a small number of the protons within the beam collide with neutron-rich atoms and cause neutrons to escape from the material 154. As is generally understood, the number of neutrons produced is dependent upon the number of protons within the proton beam, the energy of the protons, the type of the neutron-rich material and the thickness of the neutron-rich material.

In the preferred embodiment, the neutron-rich material 154 is comprised of a plate of Beryllium as this material exhibits the characteristic of having a large number of neutrons that can be generated as a result of a proton beam impinging upon the plate of Beryllium. It can be appreciated, however, that any number of other materials which exhibit this characteristic can be used. The Beryllium plate 154 is detachably mounted to the bracket 160 which allows the operator of the multiple particle beam therapy system 100 to position plates 154 of different thicknesses in front of the proton beam 161 to produce different ratios of neutrons to protons in the multiple particle beam 170. It can also be appreciated that the plate 154 could have varying thicknesses which would allow the operator to vary the ratio of neutrons to protons by simply adjusting the position of the plate 154 relative to the beam as it exits the nozzle 150.

The neutrons generated by the atomic collisions travel in generally the same direction as the proton beam 161. Hence, a multiple particle beam 170 propagates outward from the neutron-rich material 154 towards the patient 142. The protons within the multiple particle beam 170 are still directed and focused towards a target isocenter 144 within the body of the patient 142 so that the protons exhibit the Bragg peak phenomenon at the target isocenter and release a substantial portion of their energy in the proximity of the target isocenter 144. It will be appreciated that the calculations of the desired energy of the proton beam should take into consideration that the beam is travelling through the neutron-rich material in order to have the Bragg peak of the protons occur in the proximity of the desired target isocenter within the patient's body.

Further, the neutron source 104 and the energy and distribution of the proton in the proton beam can be selected so that substantially all of the protons collide with neutrons in the neutron source 104. This will result in the isocenter being bombarded with a beam that is comprised solely of neutrons. Hence, the preferred embodiment discloses a system for producing neutrons for treatment of a patient that is comprised of a neutron source and a proton treatment system.

The neutrons released from the neutron-rich material 154 propagate in a generally Gaussian shaped distribution, in which most of the neutrons are at or near the center of the path of the proton beam 161. Hence, a significant number of neutrons travel towards and through the target isocenter 144 within the body of the patient. These neutrons combine with the protons to destroy or damage tissue containing the malignant cells in the target isocenter 144. It is generally known that the Radio Biologic Effect (RBE) of a neutron is approximately 30-40% greater than the Radio Biologic Effect (RBE) of a proton. Hence, the multiple particle beam 170 produced by the present invention has a higher overall RBE than a proton particle beam alone and can thus be more effective in destroying cells of tumors, cancerous growths, etc.

Due to the destructive potential of neutrons relative to protons, it is generally desirable to limit the total number of neutrons in the multiple particle beam 170 to a small percent, for example, less than 10%, of the total particles within the beam 170 to thereby limit the amount of collateral damage to healthy tissue and cells adjacent the target isocenter 144. It may also be desirable, in some circumstances, to position the plate of neutron-rich material 154 immediately adjacent the entry site of the beam into the patient (e.g., at the patient's skin) to minimize the spread of the neutrons in the multiple particle beam 170.

The foregoing description has involved the production of the neutrons by directing the proton beam through a plate of neutron-rich material. It should be appreciated, however, that the exact manner in which the beams are generated, including the configuration of any neutron-rich material, can be varied without departing from the scope of the present invention.

It can further be appreciated that the exact configuration and composition of the multiple particle beam will be selected on a case by case basis depending upon the type of cells and the position of the cells within the patient's body that are to be targeted. Hence, the actual use of the system will vary depending upon the circumstances surrounding the treatment of the patient.

Although the foregoing description of the preferred embodiment of the present invention has shown, described and pointed out the fundamental novel features of the invention, it will be understood that various omissions, substitutions, and changes in the form of the detail of the apparatus as illustrated, as well as the uses thereof, may be made by those skilled in the art, without departing from the spirit of the present invention. Consequently, the scope of the invention should not be limited to the foregoing discussion, but should be defined by the appended claims.