1. Field of the Invention
The invention is in the field of particle sources and more specifically in the field of particle sources configured for medical applications.
2. Related Art
It has been shown that high-energy particles can be advantageously used for medical treatment of cancer. These high-energy particles typically have energies greater than 20 MeV (million electron volts). For example, protons with energies between 70 MeV and 250 MeV can be used to deposit energy at a very precise depth within a human body.
High-energy protons are generated in a particle accelerator and delivered to a patient at a treatment station. A typical treatment station includes an adjustable gurney or chair configured to position the patient relative to a fixed proton beam. In some instances, the output of the particle accelerator is directed through two alternative paths using particle transport optics such as magnets and electric fields. For example, in one instance a first set of particle transport optics is used to direct protons from above a patient and a second set of particle transport optics is used to direct protons toward the patient from the side at an angle 90 degrees from the first set of particle transport optics. One limitation of this arrangement is that each separate path requires a separate set of expensive particle transport optics and a separate particle beam nozzle.
During a treatment the depth of proton penetration and the position of the proton beam may be varied in order to treat a three dimensional volume within a patient. Depth control is achieved by varying the energy of the protons. This variation can be achieved by passing the protons through varying lengths of an energy adsorbing material or by using a particle source capable of generating particles at selectable energies. The proton beam may be applied over an area perpendicular to the depth dimension by either scanning or scattering the proton beam. Scattering or energy variation of the proton beam is optionally performed in more than one stage. For example, a first scattering step may be applied as the protons leave the particle accelerator and a second scattering step may be applied after the protons pass through final beam steering elements. Two steps are required when the final beam steering elements cannot handle a desired final spatial or energetic distribution.
A path through which particles are transported typically includes a proton nozzle. Proton nozzles can be designed for special purposes, for example, double scattering nozzles, single scattering nozzles, scanning nozzles, and other specialized nozzles known in the art. Different medical treatments require the use of different proton nozzles each weighing one thousand or more pounds and costing hundreds of thousands of dollars. Changing nozzles is a time consuming and labor intensive process that limits the flexibility of treatments particularly between successive patients and causes system downtime.
For the various reasons discussed above, and additional reasons, there is a need for improved sources of high-energy particles.