US 20100308235 A1
Interposing a programmable path length of one or more materials into a particle beam modulates scattering angle and beam range in a predetermined manner to create a predetermined spread out Bragg peak at a predetermined range. Materials can be “low Z” and “high Z” materials that include fluids. A charged particle beam scatterer/range modulator can comprise a fluid reservoir having opposing walls in a particle beam path and a drive to adjust the distance between the walls of the fluid reservoir under control by a programmable controller. A “high Z” and, independently, a “low Z” reservoir, arranged in series, can be used. When used for radiation treatment, the beam can be monitored by measuring beam intensity, and the programmable controller can adjust the distance between the opposing walls of the “high Z” reservoir and, independently, the distance between the opposing walls of the “low Z” reservoir according to a predetermined relationship to integral beam intensity. Beam scattering and modulation can be done continuously and dynamically during a treatment in order to deposit dose in a target volume in a predetermined three dimensional distribution.
33. An apparatus for scattering and/or modulating a range of a charged particle beam, the apparatus comprising:
high Z material having a path length in a path of a charged particle beam;
low Z material having a path length in the path of the charged particle beam, at least one of the high Z and low Z materials including a liquid; and
a controller configured to adjust the path lengths of the high Z and low Z materials during exposure of a target to the charged particle beam.
34. The apparatus of
35. The apparatus of
36. The apparatus of
37. The apparatus of
38. The apparatus of
a source of charged particles that provides the charged particle beam.
39. The apparatus of
40. The apparatus of
41. The apparatus of
42. The apparatus of
a beam monitor configured to measure intensity of the charged particle beam, the beam monitor communicating the intensity to the controller, the controller adjusting the low Z and, independently, the high Z path lengths according to integral intensity.
43. The apparatus of
44. A method of scattering and/or modulating a range of a charged particle beam, comprising:
directing the charged particle beam through a high Z material having a path length in a charged particle beam path;
directing the charged particle beam through a low Z material having a path length in the charged particle beam path, at least one of the high Z and low Z materials including a liquid; and
adjusting the path lengths of the high Z and low Z materials during exposure of a target to the charged particle beam.
45. The method of
46. The method of
47. The method of
measuring intensity of the charged particle beam; and
wherein adjusting the path lengths of the high Z and low Z materials includes adjusting the path lengths according to the intensity.
48. The method of
49. The apparatus of
50. The method of
producing the charged particle beam.
51. The method of
52. The method of
53. The method of
54. The method of
This application is a continuation of U.S. application Ser. No. 11/724,055, filed Mar. 14, 2007, now U.S. Pat. No. 7,718,982, which is a continuation of Ser. No. 10/949,734, filed Sep. 24, 2004, now U.S. Pat. No. 7,208,748, which claims the benefit of U.S. Provisional Application No. 60/590,088, filed on Jul. 21, 2004. The entire teachings of the above applications are incorporated herein by reference.
Charged particles have been used in the field of radiation therapy for cancer for more than 50 years. In order to create a clinically useful dose distribution that conforms to the shape of the target volume within the patient, a number of beam shaping and modulating materials are interposed between the particle accelerator and the patient. A proton beam has a significant clinical advantage over conventional high energy x-ray beams which attenuate exponentially in tissue. The physics of the energy deposition is advantageous and different for protons compared to high energy x-rays (photons).
A proton beam delivers a small entrance dose, then delivers a large dose as the protons stop in the tissue. This large deposition of dose at the end of the tissue penetration range of the protons is called a Bragg peak, after the physicist who discovered the effect.
The beam, emerging from the particle accelerator, is shaped by inserting devices and materials into the beam. One objective of shaping the beam is to deliver a uniform dose of radiation throughout the volume of a target, such as a tumor in a patient's body. The range (i.e. the depth of beam penetration into the tissue) needs to be modulated to ensure that a uniform or other predetermined dose of radiation is delivered between the proximal and the distal surfaces of the target. (As used herein, the terms “proximal” and “distal” are used with respect to the beam path. The term “proximal” specifically refers to the area of entry of a beam into a target.) Furthermore, the beam needs to be spread out laterally in order to treat large tumors. (As used herein, the terms “lateral” refers to any direction substantially perpendicular to the beam path.) The beam is manipulated and shaped by a series of scatterers and apertures.
In a beam shaping system, the beam is first directed at a first scatterer/range modulator, which scatters the proton beam through an angle wide enough to treat a therapy field of about 20-30 cm. Following scattering and range modulation by the first scatterer, the beam is directed to a compensated second scatterer. The purpose of this element is to flatten the cross section of the beam emerging from the first scatterer. This allows the Bragg peak to be planar and uniform in intensity at the isocenter distance.
The third element of the beam shaping system is a range matching bolus. This is typically a thick cylinder of acrylic plastic into which the inverse of the 3-dimensional shape of the distal surface of the target volume has been machined. This element also includes a correction for the profile of the external surface of the patient from the beam direction and a correction for the inhomogenieties such as bone or air in the path. Most tissue is substantially equivalent to water, but corrections for these different materials can be calculated from the CT image data set. The resulting three dimensional structure is placed in the beam path to ensure that the Bragg peak conforms to the distal surface of the target, resulting in minimum dose to critical structures located beyond the target volume.
The fourth element of the beam shaping system shapes the beam laterally to match the shape of the target volume as seen from the direction of the beam's origin by using apertures made specifically for that treatment. This is usually accomplished by machining a profiled aperture into a thick piece of brass or other high Z material and placing it in close proximity to the patient. The beam is limited in lateral extent by this element and therefore conforms to the shape of the target volume.
Interposing a programmable path length of one or more scattering and/or absorbing materials into a particle beam may be used to modulate scattering angle and beam range in a predetermined manner. A charged particle beam scatterer/range modulator can comprise high Z material, having an adjustable path length in a particle beam path, low Z material having an adjustable path length in the particle beam path, and a programmable controller that independently adjusts the high Z and low Z path lengths during exposure of a target to the beam. The high Z and the low Z materials can be liquid. The path length of the low Z material and, independently, the path length of the high Z material can be continuously adjustable.
The charged particle beam scatterer/range modulator can comprise a fluid reservoir having opposing walls in a particle beam path, a drive to adjust the distance between the walls of the fluid reservoir, and a programmable controller for the drive to adjust the distance between the walls of the reservoir during exposure of a target to the beam. The distance between the opposing walls of the reservoir can be continuously adjustable. A first and second fluid reservoir can be arranged in series in the particle beam path. The first and the second reservoirs can independently contain high Z and low Z materials. The distance between the opposing walls of the first reservoir and, independently, the distance between the opposing walls of the second reservoir can be continuously adjustable.
A source of charged particles that provides a charged particle beam and a charged particle beam scatterer/range modulator can be employed in a radiation treatment apparatus. A beam monitor can be used to measure beam intensity and communicate beam intensity to the programmable controller. The programmable controller can adjust the low Z and, independently, the high Z path lengths according to a predetermined relationship between the time integral of the beam intensity and the desired path lengths of the low Z and high Z materials. The programmable controller can adjust the low Z and, independently, the high Z path lengths continuously and dynamically.
The source of charged particles can be a cyclotron. The cyclotron can be a synchrocyclotron. Any charged particles may be used, for example, the charged particles can be protons.
The high Z material and the low Z material of a charged particle beam scatterer/range modulator can be disposed in an extraction channel of the synchrocyclotron. Where the charged particle beam scatterer/range modulator comprises a fluid reservoir, having opposing walls in a particle beam path, such fluid reservoir can similarly be disposed in an extraction channel of the synchrocyclotron.
Embodiments of the present invention have a number of advantages. By independently and continuously changing thicknesses of high Z and low Z material, the path of the particle can be varied continuously over the course of a treatment. This can effectively produce uniquely variable, substantially arbitrary profiles of spread out Bragg peaks, thus delivering both a conformal and a non-uniform dose of radiation to the target. The first scatterer/range modulator of the present invention matches the dose deposition by the beam to the treatment volume in three dimensions, resulting in a highly conforming dose distribution. This leads to the best clinical outcome for the patient. The local control rate of the cancer treatment increases with increasing dose to the tumor, while the complication rate (due to unnecessary dose to critical structures) increases with the dose given to the surrounding normal tissue. By using a precisely shaped proton beam, the ratio of treatment volume dose to the dose given to surrounding tissue is increased markedly over treatments given with photon (x-ray) beams.
The use, in some embodiments, of synchrocyclotron as a source of charged particles allows the present invention to avoid relying on a variable energy beam. Furthermore, the operation of the device of the present invention can be controlled by a programmable processor in a continuously variable manner by adjusting the timing of the motion of the high Z and low Z materials to generate a predetermined, non-uniform spread out Bragg peak.
In addition to the regular clinical scenarios, there is at least one special case of scattering and range modulation where a higher intensity, small beam is required, such as in the case of treating eye tumors or macular degeneration. These special cases have a shallow depth of penetration, a very small field size and the treatment time is to be minimized. In this case, the second compensated scatterer is not employed, as the field size is very small. The first scatterer/range modulator of the instant invention is particularly advantageous for this special case application.
This invention uses the underlying physical principles employed in the past and combines them with modern control system technology and a novel geometry to create a novel beam scattering and range modulation apparatus that can programmatically deliver not only the same performance as fixed scatterer/modulator components, but also uniquely variable profiles modulated in time to generate dose distributions that can be more highly conformal to the target volume. The ability to continuously and independently vary the beam path lengths through the “high Z” and “low Z” materials avoids the problem of having to plan and deliver a treatment does of radiation in a finite number of fixed spread out Bragg peaks.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Although this invention is applicable to all charged particle beams, this discussion will focus on proton beams for radiation therapy as an illustrative and advantageous example.
As discussed above, the proton beam emerging from a particle accelerator is shaped and modulated by a number of devices and material interposed in the beam path.
An embodiment of the present invention is a charged particle scatterer/range modulator, that, in some embodiments, can be used in common implementations of proton beam radiation therapy systems as a first scatterer.
The input 102 into the system 100 is, typically, the size and location of the target volume to be treated and the external contour of the patient. Target volume parameters 102 are used by the treatment planning system 104 to prescribe a three dimensional dose distribution to conformally deliver the dose to the target volume. The output of treatment planning system 104 is communicated to the proton therapy system controller 106, that generates a series of parameters used by different subsystems to implement the treatment. These parameters include distal extent of Bragg peak and depth of spread out Bragg peak 108 and calculations 110 of high and low Z path lengths as a function of integral dose, which are based on parameters 108. The parameters important to the subsystem comprising the programmable first scatterer/range modulator 112 are the path length of high and low Z material to be interposed into the proton beam as a function of integral dose as measured by the beam monitor 114. If the output of the accelerator 116 was known to be constant over time, the path length could be programmed with respect to time. In this embodiment, use of the information directly from the beam monitor 114 removes the constraint that the output of the accelerator be constant with time.
The calculated path lengths with corrections for the measured integral dose, are converted by first scatterer/range modulator control system 118 into high Z and low Z position commands 120 for linear actuators 122 and 123 that vary the path lengths 124 and 125 of the high Z and low Z materials, respectively. The high Z and low Z materials can be solid, liquid or gaseous. Liquid materials are preferred. In a preferred embodiment, linear actuators 122 and 123 are linear motors/encoders. The encoders measure the actual position and servo loops within the system (shown in greater detail with reference to
Beam 126, produced by particle accelerator 116, which, in one embodiment, is a cyclotron, is monitored by beam monitor 114 and modulated by the first scatterer/range modulator of the present invention 112. After passing through the first scatterer 112, beam 126 passes through the second compensated scatterer 128, such as the one shown in
Following continuing lateral expansion and beam conditioning at the second scatterer 128, beam 126 is further shaped by range compensating bolus 130 and, laterally, by final conformal aperture 132 before entering target volume 134 within patient 136.
Two alternative embodiments of first scatterer/range modulator 112 of
To provide reliable fluid sealing over a long life, the systems 202 and 204 include welded metal bellows 212 and 214, respectively. Bellows 212 and 214 function as expandable side walls that, together with the opposing walls 216, 218 (system 202) and 220, 222 (system 204), form fluid reservoirs of adjustable volume disposed in a particle beam path. Referring to device 200 as shown in
Referring to device 200 as shown in
Referring to device 200 as shown in
Linear bearings rail 240 constrains the motion of the bellows 212 and 214 and extensions 226, 226′ and 224, 224′ to be substantially co-linear with the particle beam axis 208.
A pair of linear motors/encoder, such as actuators 122 and 124 shown in
The fluids in the bellows are substantially incompressible. Therefore, provision is made for a set of expansion reservoirs, also constructed of welded metal bellows in this embodiment. Referring to
Referring again to
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.