The present invention relates to an apparatus generating and selecting ions used in a heavy ion cancer therapy facility according to independent claims.
From U.S. Pat. No. 4,870,287 a proton beam therapy system is known for selectively generating and transporting proton beams from a single proton source. The disadvantage of such a system is, that the flexibility to treat patients is quite limited to relatively low effective proton beams.
It is an object of the present invention to provide an improved apparatus for generating and selecting different ions useful in an ion beam cancer therapy facility.
This object is achieved by the subject matter of independent claim 1. Features of preferred embodiments are defined by dependent claims.
According to the invention an apparatus is provided for generating, extracting and selecting ions used in an ion cancer therapy facility. The apparatus comprises an independent first and an independent second electron cyclotron resonance ion source for generating heavy and light ions, respectively. Further is enclosed a spectrometer magnet for selecting heavy ion species of one isotopic configuration positioned downstream of each ion source; a magnetic quadrupole triplet lens positioned downstream of each spectrometer magnet; a switching magnet for switching between high-LET ion species and low-LET ion species of said two independent first and second ion sources. An analyzing slit is located at the image focus of each spectrometer magnet and a beam transformer is positioned in between the analyzing slit and the magnetic quadrupole triplet.
Such an apparatus has the advantage, that the possibility to help patients is largely improved by providing two independent ion sources and a switching magnet to select the proper ion species for an optimal treatment. Further the apparatus according to the present invention has the additional advantage that two independent spectrometer lines (one for each ion source) increase the selectivity of the apparatus and improve the purity of the ion species by separating with high accuracy the ion species selected for acceleration in the linac from all the other ion species extracted simultaneously from the ion sources.
For the intensity controlled rasterscannner ion beam application system different beam intensities within an intensity range of 1/1000 are provided in a preferred embodiment of the invention for each individual synchrotron cycle. The apparatus according to the present invention has the advantage to control the beam intensity at a low energy level in that the beam is destroyed along a low energy beam transport (LEBT) line in between the magnetic quadrupol triplet and an radio frequency quadrupole accelerator (RFQ). In particular, irises with fixed apertures are provided after a switching magnet as well as before and after a macropole chopper and at an RFQ entrance flange. An intensity measurement of the relative intensity reduction versus the magnet current of the center quadrupole of the magnet quadrupole triplet lens downstream of the image slit of the spectrometer is carried out for the apparatus of the present invention and shows that the beam intensity is reduced by about a factor of 430 starting from the default setting of the quadrupole magnet down to zero current. A further reduction of the beam intensity leading to a degradation factor of 1000 can be achieved by an additional reduction of the field of the third quadrupole of the magnetic quadrupole triplet. A very smooth curve is obtained, providing a good reproducibility of the different intensity levels.
Therefore, the present invention avoids unnecessary radioactive contamination of the machine since beam intensity is controlled at the lowest possible beam energy, i.e. in said low energy beam transport line. Because the synchrotron injection scheme is not changed for the different beam intensity levels, i.e. the number of turns injected into the synchrotron are the same in all cases, the full dynamic range of 1000 is provided by the intensity control scheme in the LEBT according to the present invention. In the apparatus of the present invention the beam loss occurs mainly in the LEBT, i.e. the relative intensity reduction is almost the same measured directly behind the LEBT at a low energy level and measured in the Therapy beam line at an high energy level.
Furthermore, beam profiles are measured at different locations along the accelerator chain and at the final beam delivery system of the therapy beam line. No differences could be observed in the beam profiles as well as in the beam positions for the different beam intensities. This is a very important advantage of the present invention in order to provide reliable and constant and not intensity dependent beam parameters at the treatment locations particularly when the when the apparatus of the present invention is applied for a heavy ion cancer therapy facility.
The beam transformer positioned in between the analyzing slit and the magnetic quadrupole triplet has the advantage to measure and monitor one-line the ion beam current of the ion species selected for acceleration without destroying the ion beam. Because this transformer is positioned upstream of the magnetic quadrupole triplet used for the intensity reduction the beam transformer monitors continuously the non-degraded ion beam current while intensity of the linear accelerator beam can be changed from pulse to pulse using triplet magnets. This is very important for an on-line monitoring of the performance of the selected ion source.
In a first preferred embodiment a solenoid magnet is located at the exit of each ion source. This embodiment of the present invention has the advantage that the ion beams extracted of each ion source are focused by a solenoid magnet into the object point of the spectrometer.
In an other preferred embodiment a magnetic quadrupole singlet is positioned downstream of each ion source. This quadrupole singlet has the advantage to increase the resolution power of each spectrometer system and to provide a flexible matching between the ion sources and the spectrometer systems.
In a further preferred embodiment the ion sources comprise exclusively permanent magnets. These permanent magnets provide a magnetic field for the ion sources and have the advantage that no magnet coils are required, which would have a large power consumption for each ion source. Additionally to the large power consumption these magnet coils have the disadvantage, that they need a high pressure water cooling cycle, which is avoided in the case of permanent magnets within the ion sources of the present invention. This has the advantage to reduce the operating costs and increase the reliability of the apparatus of the present invention.
A further preferred embodiment of the present invention comprises beam diagnostic means which are located upstream each spectrometer magnet. Such beam diagnostic means can measure the cross-sectional profile of the beam and/or the totally extracted ion current. Said beam diagnostic means preferably comprises profile grids and/or Faradays cups.
A further embodiment of the present invention provides a beam diagnostic means located at each image slit. This embodiment has the advantage to measure the beam size and beam intensity for different extracted ion species and to record a spectrum.
In a preferred embodiment of the invention, said focusing solenoid magnet is positioned downstream of said macropulse chopper and upstream of said radiofrequency quadrupole accelerator. This has the advantage that the beam is focused by the solenoid magnet directly to the entrance electrodes of the radio frequency quadrupole within a very short distance between the solenoid lens and the beginning of the RFQ electrodes of about 10 cm.
A further preferred embodiment of the present invention provides diagnostic means comprising a Faraday cup and/or profile grids within the low energy beam transport system (LEBT) downstream of a switching magnet. These diagnostic means are not permanently within the range of the ion beam, but are positioned into the range of the ion beam for measurement purposes. The Faraday cup captures all ions passing the switching magnet and the profile grids measure the local distribution of ions within the beam cross section. During an operation cycle these diagnostic means are driven out of the range of the ion beam.
In a further preferred embodiment of the present invention the alternating stems within said radio frequency quadrupole are mounted on a common water cooled base plate. This has the advantage that the energy loss of the RFQ is conducted toward to outside of the chamber and do not damage the stems or the electrodes of the RFQ.
In a further preferred embodiment of the present invention the base plate is made of an electrical insulating material. This has the advantage that the stems are not short circuit, though they are acting as inductivity whilst said mini-vane pairs forming electrodes are acting as capacitance for a xcex/2 resonance/structure.