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After 25 years of successful research in the nuclear and radiation physics domain, the KVI-CART research center in Groningen is upgraded and re-established as the PARticle Therapy REsearch Center (PARTREC). Using the superconducting cyclotron AGOR and being embedded within the University Medical Center Groningen, it operates in close collaboration with the Groningen Proton Therapy Center. PARTREC uniquely combines radiation physics, medical physics, biology and radiotherapy research with an R program to improve hadron therapy technology and advanced radiation therapy for cancer. A number of further upgrades, scheduled for completion in 2023, will establish a wide range of irradiation modalities, such as pencil beam scanning, shoot-through with high energy protons and SOBP for protons, helium and carbon ions. Delivery of spatial fractionation (GRID) and dose rates over 300 Gy/s (FLASH) are envisioned. In addition, PARTREC delivers a variety of ion beams and infrastructure for radiation hardness experiments conducted by scientific and commercial communities, and nuclear science research in collaboration with the Faculty of Science and Engineering of the University of Groningen., Proceedings of the 15th International Conference on Heavy Ion Accelerator Technology, HIAT2022, Darmstadt, Germany

In Proton therapy, the potential of using high dose rates in cancer treatment is being explored. High dose rates could improve efficiency and throughput in standard clinical practice, allow efficient utilization of motion mitigation techniques for moving targets, and potentially enhance normal tissue sparing due to the FLASH effect. However, high dose rates are difficult to reach when lower energy beams are applied in cyclotron-based proton therapy facilities, because they result in large beam sizes and divergences downstream of the degrader, incurring large losses from the cyclotron to the patient. In current facilities the emittance after the degrader is reduced using circular collimators (emittance selection collimators after the energy degrader); this however does not provide an optimal matching to the acceptance of the following beamline, causing a low transmission for these energies. We, therefore, propose to use a collimation system asymmetric in both beam size and divergence, which allows to maximize the transmission of low energy beams, while resulting in symmetric emittance in both planes as required for a gantry system. Using a specifically designed asymmetric collimation system, we found in simulations that low energy (70 MeV) beam transmission increases almost 6 times compared to the currently used circular collimator system [1]. Such a system could easily be implemented in facilities interested in increasing dose rates for efficient motion mitigation and FLASH experiments alike. [1] Maradia et. al., “A new emittance selection system to maximize beam transmission for low-energy beams in cyclotron-based proton therapy facilities with gantry,” doi: https://doi.org/10.1002/mp.15278.

Purpose or Objective Our objective is to design a universal dynamic energy modulator (ridge filter) for PBS proton therapy. By using a ridge filter, the Bragg peak is broadened, thus lowering the number of energies required for homogeneous target coverage. Treatment delivery time in PBS proton therapy depends on beam-on time and the dead time (time required to change energy layers and/or lateral position). By lowering the number of required energies, we want to reduce the treatment delivery time. Material and Methods To reduce the number of energy layers, we developed a new energy modulation unit that comprises two identical ridge filters placed just before the isocenter. Both ridge filters are movable relative to each other to change the Bragg peak’s characteristics dynamically. For predicting the Bragg peak shape with the ridge filter, we used Monte Carlo simulations implemented in TOPAS with the beam model of PSI Gantry 2. To compare the reduction in energy layers with ridge filter, we generated eight different spread out Bragg peaks (SOBPs) with a thickness range from 4 to 11 cm with and without the ridge filter. Results We showed that a maximum broadening of the Bragg peak is achieved (almost 2 cm SOBP) if the filter is aligned, peaks with peaks. However, if the filter is aligned peak with valley, the ridge filter acts as a range shifter. Additionally, we showed an 11 cm wide SOBP generated by the ridge filter while aligning peak with valley for the first two high-energy beams (to get the sharper fall-off) and for the remaining lower energies, the filter is aligned in peak-to-peak position (to maximize the Bragg peak broadening). In this way, the dynamic ridge filter produces a sharper distal fall-off compared to a normal ridge filter. And we showed the number of energy layers required to generate different widths of SOBP with and without ridge filter. With the dynamic ridge filter, we managed to reduce the required energy layers by a factor of three compared to a SOBP generated without a ridge filter. Conclusion In this study, we showed that by using a newly developed dynamic ridge filter we could reduce the number of energy layers required to generate different SOBP by a factor of three while being independent of energy. As we can use the same ridge filter design for different types of tumors, the use of a dynamic ridge filter will not increase the complexity of treatment planning. As this design is not patient-specific or beam model-specific, it is easily adaptable for other proton therapy facilities, too.

In proton therapy, high dose rates can reduce treatment delivery times, allowing for efficient mitigation of tumor motion and increased patient throughput. With cyclotrons, however, high dose rates are difficult to achieve for low-energies as, typically, the emittance after the degrader is matched in both transversal planes using circular collimators, which does not provide an optimal matching to the acceptance of the following beamline. Transmission can however be substantially improved by transporting maximum acceptable emittances in both orthogonal planes, but at the cost of gantry angle-dependent beam shapes at isocenter. Here we demonstrate that equal emittances in both planes can be recovered at the gantry entrance using a thin scattering foil, thus ensuring gantry angle-independent beam shapes at the isocenter. We demonstrate experimentally that low-energy beam transmission can be increased by a factor of 3 using this approach compared to the currently used beam optics, whilst gantry angle-independent beam shapes are preserved. We expect that this universal approach could also bring a similar transmission improvement in other cyclotron-based proton therapy facilities., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Objective: We studied the feasibility of pencil beam scanning (PBS) proton therapy treatments within a single breath-hold at PSI’s Gantry 2. Treatment delivery time in PBS proton therapy depends on beam-on time and the dead time between proton spots (time required to change energy and/or lateral position). We studied ways to reduce beam-on and lateral scanning time, without sacrificing dosimetric plan quality, aiming at a single field delivery time of 15 seconds at maximum. We tested this approach on five lung cases with varying target volume. Methods: To reduce the beam-on time, we increased the beam current at the isocenter by developing new beam optics for PSI’s PROSCAN beamline and Gantry 2. Experimentally we obtained up to factor 5 higher transmission efficiency for all proton energies. To reduce the dead time between the spots, we used spot-reduced plan optimization. First, a 3-field IMPT treatment plan was generated for all three-lung cases using the in-house clinical planning system ‘PSIplan’. Spot-reduced plans were subsequently generated while mimicking relevant dosimetric plan parameters of the clinical plans to ensure comparable plan quality. The spot reduction technique reduced the number of spots by 95% compared with the clinical planning system for the lung cases considered. For the clinical and spot-reduced plans, 2-Gy(RBE) fractions were delivered with PSI’s Gantry 2 using the clinical and transmission-efficient beam-optics, respectively. We extracted delivery times, including both beam-on time and dead time, from the log-files. Results: A single field delivery with PSI plan and clinical beam optics takes about 40 to 100 seconds depending on the size, shape, and location of the target. The use of new optics and spot-reduced planning reduced delivery time by a factor of 4 to 6 and it is possible to deliver a single field within 15 seconds of the single breath-hold window for a very large lung case. For intermediate and small lung tumors, it is possible to deliver a field even within 7-10 seconds. Conclusion: In this feasibility study, we showed that it is possible to deliver a single field using intensity modulated proton therapy within a single breath-hold for locally advanced non-small cell lung cancers. To this goal, both beam-on time and dead time were shortened, using new beam optics in the delivery and spot reduction optimization in the planning. This is a very promising option to treat moving targets effectively with a breath-hold technique.

Most of the conventional beam optics of cyclotron-based proton gantries were designed to provide point-to-point focus in both planes with an imaging factor between 1 and 2 from the entrance of the gantry to the patient. This means that a small beam size at the gantry entrance is required to achieve the required small beam size at the patient. Due to the typically used beam emittance, this in turn results in large beam divergence at the gantry entrance, increasing the possibility of beam losses along the gantry as the beam envelope gets close to the apertures. To maximize transmission through the gantry, we propose a novel beam optics concept using 3:1 imaging. It reduces the beam divergence at the gantry entrance by factor 3 while still achieving a small beam size at the patient. The beam envelope is better controlled and keeps clear of the apertures compared to the 1:1 or 1:2 imaging beam envelope. For PSI Gantry 2, the novel 3:1 imaging beam optics increase the proton beam transmission for lower energies by 40% compare to 1:1 imaging beam optics. The usage of small imaging factors can help to maximize transmission for different gantry lattices, thus reducing treatment times., Proceedings of the 12th International Particle Accelerator Conference (IPAC 2021), ISBN:978-3-95450-214-1

Treatment delivery time in proton therapy depends on beam-on time and the time required to change energy layers and/or lateral position. For cyclotron-based facilities, low energy beams (100-70 MeV) are inefficiently transported through beamlines due to their large emittance after the degrader (~400 pi*mm*mrad 2-sigma emittance), whereas the beamline and Gantry can only transport small emittances (e.g. 30 pi*mm*mrad for PSI Gantry 2) resulting in a low dose rate at the patient and increased beam-on time. In this work, we aim to maximize the emittance transported through the gantry for low energy beams. By choosing a small divergence, but large beam size, at the gantry entrance, it is possible to transport higher emittances through the gantry without compromising transmission. Additionally, in order to retrieve small beam sizes at the patient, we propose a 2:1 imaging of the gantry beam optics between the gantry coupling point and the patient. This concept has been experimentally validated on Gantry 2 at PSI. A beam with an emittance of 90 pi*mm*mrad and ~60% transmission was transported through the gantry. As we are transporting only a narrow part of the large Gaussian beam after the degrader, this 3 times higher emittance corresponds to ~3 times more transported particles. With this, treatment times for example cases (lung and liver) have been estimated to reduce by a factor of 2 to 3. Such a beam optic could therefore have substantial potential for reducing treatment times, and be of particular advantage for the treatment of moving targets.

At PSI, a dedicated proton therapy facility, with a superconducting cyclotron, delivers 250 MeV beam energy, pulsed at 72.85 MHz. The measurement of beam currents (0.1-10 nA) is generally performed by ionisation chambers (ICs), but at the expense of reduced beam quality, and scattering issues. There is a strong demand to have an accurate signal with a minimal beam disturbance. A cavity resonator, on fundamental resonance mode, has been built for this purpose. The cavity, coupled to the second harmonic of the pulse rate, provides signals proportional to the beam current. It is installed in a beamline to measure for the energy range 238-70 MeV. Good agreement is reached between the expected and measured sensitivity of the cavity. The cavity delivers information for currents down to 0.15 nA with a resolution of 0.05 nA when integrated over one second. Its application is limited to a machine-safety monitor to trigger inter-locks, within the existing domain of the proton therapy due to the low beam current limits. With new advancements in proton therapy, especially FLASH, the cavity resonator’s application as an online beam-monitoring device is feasible., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

The beam line for radionuclide production on the PSI Cyclotron Facility starts with an electrostatic beam splitter, which peels protons of a few tens of microampere from a beam around two milliampere. The peeled beam is then guided onto a target station for routine production of a variety of radionuclides [1]. Beam Delivery Simulation (BDSIM), a Geant4 based simulation tool, enables the simulation of not only beam transportation through optics elements like dipoles and quadrupoles, but also particle passage through components like collimator and degrader [2-3]. Furthermore, BDSIM facilitates user built elements with accompanying electromagnetic field, which is essential for the modeling of the first element of the beam line, the electrostatic beam splitter. With a model including all elements from beam splitter to target, BDSIM simulation delivers a better specification of the beam along the complete line, for example, beam profile, beam transmission, energy spectrum, as well as power deposit, which is of importance not only for present operation but also for further development., Proceedings of the 22nd International Conference on Cyclotrons and their Applications, Cyclotrons2019, Cape Town, South Africa

Low beam currents (0.1-10 nA) are used for tumour treatment in the proton radiation therapy facility at PSI. The facility houses a superconducting cyclotron with extraction energy of 250 MeV pulsed at 72.85 MHz. Online measurement of the beam position is traditionally performed with the help of ionisation chambers (ICs), however, at the expense of reduced beam quality and scattering issues. There is a strong demand to have this measurement performed with minimal beam disturbance since the beam position is directly associated with the dose-rate applied. A cavity resonator, working on the principle of an electric dipole mode resonance, whose frequency is coupled to the second harmonic of the pulse rate, has been built to measure beam position in a purely non-invasive manner. Followed by a reasonable agreement between the test-bench and the simulation results, the cavity is installed in one of the beamlines. Here, we report on the measurement of the cavity BPM as a function of beam current and position and its shortcomings. The cavity BPM can deliver position information within the accuracy and resolution demands of 0.50 mm, when measured with a spectrum analyzer., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

Low proton beam intensities (0.1-40 nA) are used for medical treatment of tumours at the PROSCAN facility in Paul Scherrer Institut (PSI). A cavity resonator using four quadrants operating in a dipole mode resonance has been developed to measure beam positions at these low intensities. The TM110 resonance frequency of 145.7 MHz is matched to the second harmonic of the beam pulse repetition rate (i.e.72.85 MHz). HFSS (High Frequency Structural Simulator) provides the BPM geometry and important parameters such as pickup position; dielectric dimensions etc. Comparison of test bench measurement and simulation provides good agreement. The measured position and signal sensitivity are limited by the noise, so that a position signal can be derived at beam intensities of at least 10 nA . We will discuss potential methods to increase the sensitivity. The dipole cavity resonator can be a promising candidate as a non-invasive position di-agnostic at the low proton beam intensities used in pro-ton therapy, Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

In calculations based on particle tracking in 3D magnetic field maps alignment of the components of a magnetic lattice is essential to obtain desired properties of beam optics. In this contribution we propose a method to control and correct misalignments during the process of the beam optics design. These misalignments would result from overlapping fringe fields of different field maps. The 3D field maps are obtained from the software for electromagnetic calculations OPERA. The full 3D map is saved in the tracking coordinate system and a ROOT (An Object Oriented Data Analysis Framework) ntuple is then created for analysis. The trajectory of the reference particle is calculated by means of OPAL - open source code developed at the Paul Scherrer Institut (PSI). The transverse magnetic field profiles allow possible misalignments to be precisely determined and the corresponding corrections to be calculated. Moreover, the multipole content in discrete locations along the lattice can be controlled by performing a polynomial fit, which calculates the magnetic field harmonics with respect to the reference track. This method was used at PSI for a design of a model of the magnetic lattice for a superconducting gantry for proton therapy with a large momentum acceptance., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The present invention discloses a system (2, 2') for particle beam therapy, comprising as seen in the flow direction of the particle beam (4): a) an adjustable gantry (10, 10') for the beam delivery to a target volume, said gantry comprising: a1) a beam coupling section (6) for the incoming particle beam (4); said incoming particle beam (4) being oriented substantially horizontally thereby defining a horizontal plane; a2) a first beam bending section (8, 8') comprising a number of beam deflection and/or focusing magnets (12, 14) wherein the first bending section (8, 8') either bends the particle beam (4) with an adjustable angle into the vertical plane, or with 90 degrees in the horizontal plane, but with the mechanical possibility to rotate with an adjustable angle along the axis of the incoming particle beam (4); a3) a beam transport section (16) receiving the particle beam (4) leaving the first beam bending section (8, 8') and guiding the particle beam (4) to a second beam bending section (18); a4) the second beam bending section (18) comprising a number of beam deflection magnets and/or beam focusing magnets; a5) a beam nozzle (20) comprising a window for the exit of the particle beam (4); and b) a patient table/chair (22) being rotatable in the horizontal plane or in a plane being parallel to the horizontal plane and optionally being adjustable vertically, wherein: c) the gantry (10, 10') is supported by a tilting mechanism(24) allowing the gantry (10, 10') to be tilted vertically by an angle Φ1, Φ1 ԑ [-90°; +90°], wherein the gantry (10, 10') comprises a pivot (7, 7') being disposed in the region of the first bending section (8, 8'); and d) a rotation mechanism (26) beingdisposed in a way that the second beam bending section (18) and the beam nozzle (20) being rotatable by an angle Φ2, Φ2 ԑ [-180°; +180°] around a direction given by the angle Φ1

The beam transport system between accelerator and patient treatment location in a particle therapy facility is described. After some general layout aspects the major beam handling tasks of this system are discussed. These are energy selection, an optimal transport of the particle beam to the beam delivery device and the gantry, a device that is able to rotate a beam delivery system around the patient, so that the tumour can be irradiated from almost any direction. Also the method of pencil beam scanning is described and how this is implemented within a gantry. Using this method the particle dose is spread over the tumour volume to the prescribed dose distribution., 12 pages, Presented at the CAS- CERN Accelerator School on Accelerators for Medical Application, V\"osendorf, Austria, 26 May - 5 June, 2015

In particle therapy with protons a cyclotron is one of the most used particle accelerators. Here it will be explained how a cyclotron works, some beam dynamics aspects, its major subsystems, as well as the advantages and disadvantages of a cyclotron for this application are discussed. The difference between the standard isochronous cyclotron and the synchrocyclotron is explained. New developments are presented and especially those which aim to reduce the size of the accelerator., 11 pages, Presented at the CAS- CERN Accelerator School on Accelerators for Medical Application, V\"osendorf, Austria, 26 May - 5 June, 2015

It is the objective of the present invention to provide a degrader that has excellent degrading capabilities with, for the same energy loss in the degrader, a lower emittance increase as currently used materials, without generating a strong neutron flux and without having severe toxic characteristics. This objective is achieved according to the present invention by a degrader (2) for use in the field of the application of a particle beam (6), comprising degrading active material wherein the degrading active material comprises Boron Carbide B4C. This degrader has an amount of multiple scattering that is lower than in graphite for the same energy loss. The use of B4C increases the transmission by at typically 35% for the beam degradation to low energies, which is a significant and useful amount of beam intensity increase in particle therapy. The B4C-material does not become more radio-active than graphite, so that there will be no additional problems at service activities. Further, B4C as degrading active material does not have severe toxic properties.

The present invention provides a movable gantry (2') for delivery of a particle beam using beam scanning technique, for example for the cancer treatment in human tissue; comprising: a) an inlet section (6) for an accelerated particle beam comprising a number of quadrupole magnets; b) a first bending section (8) and optionally a second bending section (12) comprising a number of dipole and quadrupole magnets and optionally further magnets for beam correction; c) a transfer section comprising a number of quadrupole magnets and optionally further magnets for beam correction and a degrader (D); d) a last beam bending section (16) comprising a number of separate and/or combined dipole/quadrupole/higher order multipole magnets forming an achromatic section, wherein all magnets of this achromatic last bending section (16) are located downstream of the degrader (D); any dispersion in this achromatic last bending section (16) is suppressed so that it will have a momentum acceptance of more than ±5%; e) a scanning section (15) comprising two separate or one combined fast deflection magnets (K1, K2) that deflect the beam at the iso-center in a direction perpendicular to the beam direction to perform lateral scanning; and f) a beam nozzle section (18) comprising a beam nozzle and optionally beam handling equipment, such as further beam degrading or modifying elements and/or beam quality related beam verifying elements. This combination of a degrader mounted in the gantry and a design of the gantry's beam transport magnets with a large momentum acceptance creates a possibility to increase the energy acceptance of the last bending section in the gantry and implement new dose application techniques, such as a fast change of proton energy at the patient without changing the magnetic field of the last bending section in the gantry.

An increasing number of proton therapy facilities are being planned and built at hospital based centers. Many facilities use rotatable gantry beamlines to direct the proton or ion-beam at the patient from different angles. A key issue is the need to make future gantries lighter and more compact with the use of cryogen-free superconducting magnets, in particular for the final bending section which can be of large aperture. Benefits of using the superconducting technology are: (1) the possibility to have a large momentum acceptance, hence reducing the need to ramp the magnet and enabling new treatment techniques, (2) the size reduction due to a lower bend radius and (3) the weight reduction up to a factor ten. The latter will also significantly reduce the costs of the supporting structure. We present a conceptual design based on Nb3Sn superconducting combined function magnets (dipole, quadrupole, sextupole). The geometry using racetracks, the superconducting strand and cable parameters and the results of the thermal and the mechanical studies are reported. These magnets will work at a temperature of about 4.2 K cooled with cryocoolers., Proceedings of the 25th Russian Particle Accelerator Conf., RuPAC2016, St. Petersburg, Russia

Paul Scherrer Institute currently extends its PROSCAN facility with a third gantry treatment room - Gantry 3, which is realized in a research collaboration with Varian Medical Systems. The main research goals at the PROSCAN facility include further development of precise spot scanning and optimized beam delivery with low dead-time for treatment of moving targets. Consequently Gantry 3 is designed to feature advanced pencil beam scanning technology with a large scan field size of 30x40cm, integrated cone beam CT functionality and will in the future allow fast energy layer switching. The main challenge in realizing Gantry 3 is the integration of the Varian Gantry into the existing PROSCAN control system environment, allowing seamless beam operation. Installation of the additional treatment room has started in summer 2015 followed by the integration and technical commissioning phases of the Gantry in 2016, all during full operation of the existing treatment areas at our facility. We report about the special challenges and achieved performance results during commissioning of the Varian Gantry system in combination with the PSI PROSCAN facility., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The cold cathode Penning ionization gauge (PIG) type proton source of the VARIAN’s ProBeam® 250 MeV superconducting isochronous cyclotron suffers from the usual cathode/chimney erosion during operation. Furthermore, a relatively high hydrogen gas flow is needed to generate a proton beam in the µA range, which induces conditions for RF operation below optimum. In the quest to increase cathode/chimney life time and thereby directly extend service intervals, thus reducing the total cost of ownership, several experimental investigations have been performed at a dedicated test bench at PSI, Switzerland, including material studies, a detailed operation analysis and switching to a hot cathode design., Proceedings of the 21st Int. Conf. on Cyclotrons and their Applications, Cyclotrons2016, Zurich, Switzerland