High-energy Proton Beam Research Articles

First 70Zn(p,x) nuclear cross section measurements for theranostic 67Cu radionuclide production extended up to 100 MeV

In this work the nuclear reaction routes 70Zn(p,x)64,67Cu, 66,67Ga, and 65,69mZn, induced by a high-energy proton beam up to 100 MeV have been investigated. Demand for 67Cu is increasing worldwide because it is known to be one of the best radionuclides having theranostic properties. Thus, efforts to improve its global production are underway. In previous studies, experimental data about nuclear cross-section measurements on 70Zn-enriched targets induced by proton beams were limited to an energy range of up to 70 MeV. Our goal was to extend nuclear data on 70Zn over a wider and unexplored so far region from 42 MeV to 98 MeV. As a result, our data turned out to be in good agreement with the literature ones in the overlapping energy range. In addition, to the best of our knowledge, new nuclear data exceeding 70 MeV were provided, demonstrating an excellent analytical method for producing 67Cu in the extended energy range.

Design of a compact beam transport system for laser-driven proton therapy

Abstract We put forward a new design of a compact beam transport system for intense laser-driven proton therapy, where instead of using conventional pulsed solenoids, our design relies on a helical coil irradiated by a nanosecond laser pulse to generate strong magnetic fields for focusing protons. A pair of dipole magnets and apertures are employed to further filter protons with large divergences and low energies. Our numerical studies combine particle-in-cell simulations for laser-plasma interaction to generate high-energy monoenergetic proton beams, finite element analysis for evaluating the magnetic field distribution inside the coil, and Monte-Carlo simulations for beam transport and energy deposition. Our results show that with this design, a spread-out Bragg peak in a range of several centimeters to a deep-seated tumor with a dose of approximately 16.5 cGy and fluctuation around 2% can be achieved. The instantaneous dose rate reaches up to 109 Gy/s, holding the potential for future FLASH radiotherapy research.

Novel indium phosphide charged particle detector characterization with a 120 GeV proton beam

Thin film detectors which incorporate semiconductor materials other than silicon have the potential to build upon their unique material properties and offer advantages such as faster response times, operation at room temperature, and radiation hardness. To explore the possibility, promising candidate materials were selected, and particle tracking detectors were fabricated. An indium phosphide detector with a metal-intrinsic-metal structure has been fabricated for particle tracking. The detector was tested using radioactive sources and a high energy proton beam at Fermi National Accelerator Laboratory. In addition to its simplistic design and fabrication process, the indium phosphide particle detector showed a very fast response time of hundreds of picoseconds for the 120 GeV protons, which are comparable to the ultra-fast silicon detectors. This fast-timing response is attributed to the high electron mobility of indium phosphide. Such material properties can be leveraged to build novel detectors with superlative performance.

Selective electron beam sensing through coherent Cherenkov diffraction radiation

We exploit the coherent emission of Cherenkov diffraction radiation (ChDR) by a relativistic electron beam to sense its position even in the presence of other particle beams. ChDR is produced in alumina inserts embedded in the vacuum chamber walls and recorded in a narrow band centered at 30 GHz. This nontrivial solution has been implemented for plasma wakefield accelerators, where the electron beam to be sensed can copropagate with another high-energy proton beam that generates the plasma wakefield. In addition, at variance with most existing position detectors, this method is insensitive to spurious electric charges due to the presence of plasma. We present the overall design of the detector as well as experimental results obtained in the AWAKE facility at CERN. Published by the American Physical Society 2024

Laser-driven high-energy proton beams from cascaded acceleration regimes

Laser-driven ion accelerators can deliver high-energy, high-peak current beams and are thus attracting attention as a compact alternative to conventional accelerators. However, achieving sufficiently high energy levels suitable for applications such as radiation therapy remains a challenge for laser-driven ion accelerators. Here we generate proton beams with a spectrally separated high-energy component of up to 150 MeV by irradiating solid-density plastic foil targets with ultrashort laser pulses from a repetitive petawatt laser. The preceding laser light heats the target, leading to the onset of relativistically induced transparency upon main pulse arrival. The laser peak then penetrates the initially opaque target and triggers proton acceleration through a cascade of different mechanisms, as revealed by three-dimensional particle-in-cell simulations. The transparency of the target can be used to identify the high-performance domain, making it a suitable feedback parameter for automated laser and target optimization to enhance stability of plasma accelerators in the future.

Reduced interface effect of proton beam irradiation on the electrical properties of WSe2/hBN field effect transistors

Two-dimensional transition metal dichalcogenide (TMDC) semiconductors are emerging as strong contenders for electronic devices that can be used in highly radioactive environments such as outer space where conventional silicon-based devices exhibit nonideal characteristics for such applications. To address the radiation-induced interface effects of TMDC-based electronic devices, we studied high-energy proton beam irradiation effects on the electrical properties of field-effect transistors (FETs) made with tungsten diselenide (WSe2) channels and hexagonal boron-nitride (hBN)/SiO2 gate dielectrics. The electrical characteristics of WSe2 FETs were measured before and after the irradiation at various proton beam doses of 1013, 1014, and 1015 cm−2. In particular, we demonstrated the dependence of proton irradiation-induced effects on hBN layer thickness in WSe2 FETs. We observed that the hBN layer reduces the WSe2/dielectric interface effect which would shift the transfer curve of the FET toward the positive direction of the gate voltage. Also, this interface effect was significantly suppressed when a thicker hBN layer was used. This phenomenon can be explained by the fact that the physical separation of the WSe2 channel and SiO2 dielectric by the hBN interlayer prevents the interface effects originating from the irradiation-induced positive trapped charges in SiO2 reaching the interface. This work will help improve our understanding of the interface effect of high-energy irradiation on TMDC-based nanoelectronic devices.

Single high-energy arc proton therapy with Bragg peak boost (SHARP).

Because of the co-location of critical organs at risk, base of skull tumours require steep dose gradients to achieve the prescribed dosimetric criteria. When available, proton beam therapy (PBT) is often considered a desirable modality for these cases, but in many instances, compromises in target coverage are still required to achieve critical organ at risk (OAR) tolerance doses. A number of techniques have been proposed to further improve the penumbra of PBT. In the current study, we propose a novel, collimator-free treatment planning technique that combines high-energy shoot-through proton beams with conventional Bragg peak spot placement. The small spot size of the high-energy pencil beams provides a sharp penumbra at the target boundary, and the Bragg peak spots provide a higher linear energy transfer (LET) boost to the target centre. Three base of skull chordoma patients were retrospectively planned with three different PBT treatment planning techniques: (1) conventional intensity-modulated proton therapy (IMPT); (2) high-energy proton arc therapy (HE-PAT); and (3) the novel technique combining HE-PAT and IMPT, referred to as single high-energy arc with Bragg peak boost (SHARP). The Monaco 6 treatment planning system was used. SHARP was found to improve the PBT penumbra in the plane perpendicular to the HE-PAT beams. Minimal penumbra differences were observed in the plane of the HE-PAT beams. SHARP reduced dose-averaged LET to surrounding organs at risk. A novel PBT treatment planning technique was successfully implemented. Initial results indicate the potential for SHARP to improve the penumbra of PBT treatments for base of skull tumours.

Feasibility study of multiple-energy Bragg peak proton FLASH on a superconducting gantry with large momentum acceptance.

While the Bragg peak proton beam (BP) is capable of superior target conformity and organs-at-risk sparing than the transmission proton beam (TB), its efficacy in FLASH-RT is hindered by both a slow energy switching process and the beam current. A universal range shifter (URS) can pull back the high-energy proton beam while preserving the beam current. Meanwhile, a superconducting gantry with large momentum acceptance (LMA-SC gantry) enables fast energy switching. This study explores the feasibility of multiple-energy BP FLASH-RT on the LMA-SC gantry. A simultaneous dose and spot map optimization algorithm was developed for BP FLASH-RT treatment planning to improve the dose delivery efficiency. The URS was designed to be 0-27cm thick, with 1cm per step. BP plans using the URS were optimized using single-field optimization (SFO) and multiple-field optimization (MFO) for ten prostate cancer patients and ten lung cancer patients. The plan delivery parameters, dose, and dose rate metrics of BP plans were compared to those of TB plans using the parameters of the LMA-SC gantry. Compared to TB plans, BP plans significantly reduced MUs by 42.7% (P<0.001) with SFO and 33.3% (P<0.001) with MFO for prostate cases. For lung cases, the reduction in MUs was 56.8% (P<0.001) with SFO and 36.4% (P<0.001) with MFO. BP plans also outperformed TB plans by reducing mean normal tissue doses. BP-SFO plans achieved a reduction of 56.7% (P<0.001) for prostate cases and 57.7% (P<0.001) for lung cases, while BP-MFO plans achieved a reduction of 54.2% (P<0.001) for the prostate case and 40.0% (P<0.001) for lung cases. For both TB and BP plans, normal tissues in prostate and lung cases received 100.0% FLASH dose rate coverage(>40Gy/s). By utilizing the URS and the LMA-SC gantry, it is possible to perform multiple-energy BP FLASH-RT, resulting in better normal tissue sparing, as compared to TB plans.

An enhanced radiation pressure acceleration scheme for accelerating protons using the uniform density plasma channel

High-energy proton beams have broad application prospects in medical imaging, tumor therapy and nuclear fusion physics. Laser plasma acceleration is a new particle acceleration method with great potential because its acceleration gradient can reach 10&lt;sup&gt;3&lt;/sup&gt;–10&lt;sup&gt;6&lt;/sup&gt; times that of traditional acceleration method, so it can theoretically accelerate electrons and ions to high energies in the scale of a few centimeters to a few meters. Radiation pressure acceleration (RPA) is considered to be the most promising mechanism of high energy proton acceleration in laser plasma acceleration, but the Rayleigh-Taylor instability (RTI) inherent in the process of radiation pressure acceleration will cause transverse density modulation on the target surface, resulting in the premature termination of the proton acceleration process and the failure to obtain high energy proton beams. In order to obtain high-energy proton beams, an acceleration scheme combining radiation pressure acceleration with laser wakefield is proposed. In this scheme, a high-energy proton beam with peak energy of 22.2 GeV, cut-off energy of 36.4 GeV and charge of 0.67 nC is obtained by adding a uniform density plasma channel at the back end of the thin target with critical density, the cut-off energy of the high energy proton can be increased by two orders of magnitude compared with the proton only in the radiation pressure acceleration process. The results confirm that in a uniform-density plasma channel connected behind a thin target, the laser wakefield can capture protons pre-accelerated by the radiation pressure process and maintain the acceleration for a long period of time, finally obtain high-energy protons. The acceleration of protons in plasma channels with different uniform densities is also investigated in this work, and it is found that the higher the density, the higher the peak energy, cut-off energy and charge of the accelerated protons are. The combined acceleration scheme is instructive for the generation and application of high-energy proton beams.

Response of the FBX aqueous chemical dosimeter to high energy proton and electron beams used for radiotherapy research

The response of the FBX aqueous chemical dosimeter to 10 MeV electron and 100 MeV proton beams was investigated, and the results were compared with those obtained for cobalt-60 gamma rays over a dose range of 0–30 Gy. The sensitivities of the FBX dosimeter in which the absorbance values were measured at the wavelength of maximum absorption (λmax) and 548 nm are approximately the same and amount to 0.091, 0.088, and 0.081 Gy-1 for 10 MeV electrons, cobalt 60 γ-rays, and 100 MeV proton beams, respectively. The corresponding calibration coefficients are 10.99, 11.36, and 12.35 Gy, in their respective order. The molar absorption coefficients that were calculated for cobalt-60 gamma rays amount to 17824 ± 560, 16417 ± 248, and 17694 ± 437 M−1cm−1 at the wavelengths λmax, 540 nm, and 548 nm, respectively. The radiation chemical yield-G (Fe3+) at the wavelengths of λmax and 548 nm has approximately the same values and amounts to 51.1 × 10−7, 49.4 × 10−7, and 45.4 × 10−7 mol.J−1 for 10 MeV electrons, cobalt-60 γ-rays, and 100 MeV proton beams, respectively, and both of them are lower by ∼ 8% than that obtained at the wavelength of 540 nm. A linear response of the FBX dosimeters prepared in the current study was achieved up to 12 Gy, compared with the linear response up to 5 Gy reported in the previous literature. Furthermore, by measuring the absorbance values at the wavelength of the isobestic point, i.e., 555 nm, the linearity of the FBX dosimetric solution may be extended to cover the entire dose range used, i.e., 0.2–30 Gy. Consequently, with good reproducibility (less than 1%), the prepared FBX dosimeter can be utilized for radiotherapy research over the dose range of 0.2–30 Gy.

High-energy quasi-monoenergetic proton beam from micro-tube targets driven by Laguerre–Gaussian lasers

High-energy proton beams with low energy spread and angular divergence are highly valuable in various applications, such as proton therapy, ultrafast science, and nuclear physics. Laser-driven ion sources are being explored as a more compact and cost-effective alternative to conventional accelerators. However, producing high-quality proton beams using lasers has been a significant challenge. In this study, we propose a novel approach to achieve high-energy quasi-monoenergetic proton beams by utilizing a Laguerre–Gaussian (LG) laser to irradiate a solid hollow tube target. Our three-dimensional particle-in-cell simulations demonstrate that the LG laser efficiently pulls out and accelerates electrons. As these electrons exit the rear side of the tube, a charge-separation electric field for proton acceleration is self-established. Meanwhile, a considerable part of the electrons are confined to the laser axis by the ponderomotive force of the LG laser, generating a longitudinal bunching field and transverse focusing field. As a result, protons are accelerated and focused in these fields, producing a high- quality proton beam with high energy (247 MeV) and low energy spread (∼2%) using an LG laser with an intensity of W cm−2 and a tube target with an electron density of 40nc . In comparison to a standard Gaussian laser, the LG laser exhibits superior performance in terms of proton cut-off energy, energy spread, and angular divergence.

Investigating the hard X-ray production via proton spallation on different materials to detect elements.

Various atomic and nuclear methods use hard (high-energy) X-rays to detect elements. The current study aims to investigate the hard X-ray production rate via high-energy proton beam irradiation of various materials. For which, appropriate conditions for producing X-rays were established. The MCNPX code, based on the Monte Carlo method, was used for simulation. Protons with energies up to 1650 MeV were irradiated on various materials such as carbon, lithium, lead, nickel, salt, and soil, where the resulting X-ray spectra were extracted. The production of X-rays in lead was observed to increase 16 times, with the gain reaching 0.18 as the proton energy increases from 100 MeV to 1650 MeV. Comparatively, salt is a good candidate among the lightweight elements to produce X-rays at a low proton energy of 30 MeV with a production gain of 0.03. Therefore, it is suggested to irradiate the NaCl target with 30 MeV proton to produce X-rays in the 0-2 MeV range.

Radiation-Tolerant Deep Learning Processor Unit (DPU)-Based Platform Using Xilinx 20-nm Kintex UltraScale FPGA

This paper presents a platform and design approach for enabling radiation-tolerant deep learning acceleration on SRAM-based 20nm Kintex UltraScale™ FPGAs, for terrestrial and high-radiation environments. The presented platform is suitable for deep neural network (DNN) implementations with an emphasis on image classification and includes solutions to mitigate both radiation-induced Single Event Functional Interrupts (SEFIs) and network datapath corruptions. The radiation-tolerant deep learning platform combines Xilinx’s Deep Learning Processing Unit (DPU) IP, Triple Modular Redundancy (TMR) MicroBlaze soft processor IP and Soft Error Mitigation (SEM)-IP to mitigate SEFIs. Furthermore, a technique known as Fault Aware Training (FAT) was applied to effectively mitigate single event effects in the datapath. Test results from a high-energy proton beam (> 60 MeV) experiment using the ResNet-18 Convolutional Neural Network (CNN) for image classification are presented. The Single Event Upset (SEU) rate, system-level SEFI rate and neural network classification/datapath performance are compared between the radiation-tolerant platform and a standard, non-mitigated approach. Results show that datapath classification errors dominate the system response (90%) vs. SEFIs (10%). When compared to standard non-mitigated training techniques, the radiation-tolerant platform using fault aware training methods shows dramatic improvements in overall system response: the overall single event cross-section was reduced by half and 40% reduction in misclassification errors were observed. Also, datapath events with classification accuracy degradation larger than 5% were completely mitigated. The SEFI rate was reduced by 100X with implemented solutions and can be further reduced by optimizing the physical separation between TMR modules.

Study on the accidents analyses of a single channel for XADS by using MPC-LBE code

Abstract Accelerator Driven sub-critical System (ADS), which employs the high-energy proton beam generated by accelerator to bombard the target nucleus and generate spallation neutrons as external neutrons to drive and maintain the operation of its sub-critical reactor, is of great significance in nuclear waste treatment and disposal. As the instability of proton beam would affect the power level of the reactor and threaten the safety of ADS, Beam Trip (BT) and Beam OverPower (BOP) are commonly considered to be its two typical transient accidents. As for the sub-critical reactor, the Transient OverPower (TOP) is also one of typical transient accidents that should be considered, which is mainly caused by reactivity insertion under certain cases, such as SGTR (Steam Generator Tube Rupture) accident. For the subcritical reactors, the transient evolution behaviors are strongly affected by the subcriticality value. On the one hand, the subcriticality values of ADS design should take safety margin and power gain into consideration. On the other hand, the subcriticality value is variable with the burnup of reactors. So it is necessary to study the safety characteristics of the subcritical reactors under different subcriticality values, in this paper, the transient safety characteristics of a single channel for XADS under BT, BOP and TOP accidents of different subcriticality values were investigated by using MPC-LBE code.

All-optical edge-enhanced proton imaging driven by an intense vortex laser

An all-optical approach to edge-enhanced proton radiography is realized by using a relativistic vortex laser irradiating on nanometer-thick foil. In the proof-of-principle experiments, the hollow proton beam was successfully produced by the transparent target normal electric field sheath in the break-out after-burner acceleration mechanism, using a superintense Laguerre–Gauss laser with the highest intensity of the laser exceeded 1020 W/cm2. An insect was imaged with the proton beam; the leg structures on the edge were clearly captured. By contrast, the dot proton source produced by a Gaussian laser was almost completely blocked by the insect's body, losing most edge information. Hollow-structured proton beams driven by vortex lasers conquer the dot imaging limit for high-energy proton beams, which may benefit imaging of capsule implosions in inertial confined fusion, instability research on expanding plasma, and precise positioning in medical therapy.

Development of experimental and computational frameworks to predict subcooled flow boiling in the LANL Isotope Production Facility

Cooling is crucial to maintain the integrity of target systems in isotope production facilities. At Los Alamos National Laboratory (LANL)’s Isotope Production Facility (IPF), multiple encapsulated targets are stacked and irradiated in tandem with a 100 MeV, ∼250 µA proton beam. To facilitate effective heat removal, these stacked targets are separated and cooled via a series of water channels. At these beam currents, this high-energy proton beam heats the target system, likely initiating subcooled flow boiling in the cooling channels. However, in-beam monitoring of the IPF target system is not possible due to the extreme radiation environment, and the necessarily significant shielding. To better understand high-power target performance, we developed ex-situ experimental and computational frameworks to predict the behavior of subcooled flow boiling at IPF. Subcooled flow boiling experiments on Inconel 625 samples under IPF conditions (2 bar pressure, 10 GPM flow rate (i.e., 2249 kg/m2/s), 85 K subcooling) revealed that IPF's average operating power is at the early stage of boiling with a heat transfer coefficient of 48,000 W/m2/s. The proposed modeling framework enables us to predict a complete boiling curve, i.e., single-phase heat transfer, onset of nucleate boiling, two-phase heat transfer, and critical heat flux (CHF), with specification of input boiling parameters up to intermediate heat flux levels. The estimated CHF under IPF conditions is 5.2 MW/m2. Experimental data under reduced conditions (2 bar pressure, 1.5 GPM flow rate (i.e., 337 kg/m2/s), 45 K subcooling) served as validation cases for the computational modeling. This computational model can be further extended to more complicated systems replicating the real IPF configuration, for instance, to study void distribution as a function of the incident proton beam profile and coolant velocity profile of multiple cooling channels. The proposed experimental and computational frameworks provide a means to better understand cooling systems in the isotope production facilities at different accelerators, where in-beam monitoring of the cooling process is not available.

Simulation study of quasi-monoenergetic high-energy proton beam based on multiple laser beams driving

High-energy proton beams have extensive and important applications. Traditional proton accelerators are bulky and costly. The high-power laser pulse technology provides a new proton acceleration scheme based on the interaction between laser and plasma, and has the advantage of miniaturization. Furthermore, comparing with traditional proton accelerators, the proton acceleration gradient by high-power laser pulses can be increased by three orders of magnitude. The proton beams with high brightness, narrow pulse width, and good directionality can be generated in theory within a very small effective size, and they are suitable for fields such as nuclear physics and particle physics, ion beam fast ignition, medical treatment, and proton beam detection. In order to realize laser proton acceleration, a great many of researches of different target configurations and acceleration mechanisms have been reported on proton acceleration driven by ultrashort and high-power lasers. However, owing to the limitation of laser intensity, the energy of proton beam driven by a single-beam laser is difficult to improve to meet the needs of medical applications. In this paper, a new method of driving proton acceleration by multiple ultrashort high-power lasers with grazing incidence on both sides of the microstrip target is proposed. A proton beam with an energy divergence of about 3% and energy of about 165 MeV can be obtained by using the two-beam driving setting. The results of two-dimensional particle-in-cell simulation show that a large number of collimated high-energy electron charges are extracted from both sides of the solid target by laser and injected into the back of the target. A longitudinal bunching field is established on the back of the target, which drives protons to accelerate and bunch to form a quasi-monoenergetic high-energy proton beam. The research also shows that the proton beam with an energy divergence of about 2% and energy of about 250 MeV can be obtained by using four grazing ultrashort high-power lasers on both sides of the microstrip target. The mechanism of multi-laser beams driving proton acceleration provides a new idea for the energy enhancement of the proton beam, and the quasi-monoenergetic high-energy proton beam is expected to be applied to the field of medical treatment.

Study of hydrodynamic-tunnelling effects induced by high-energy proton beams in graphite

The design and assessment of machine-protection systems for existing and future high-energy accelerators comprises the study of accidental beam impact on machine elements. In case of a direct impact of a large number of high-energy particle bunches in one location, the damage range in the material is significantly increased due to an effect known as hydrodynamic tunnelling. The effect is caused by the beam-induced reduction of the material density along the beam trajectory, which allows subsequent bunches to penetrate deeper into the target. The assessment of the damage range requires the sequential coupling of an energy-deposition code, like FLUKA, and a hydrodynamic code, like Autodyn. The paper presents the simulations performed for the impact of the nominal LHC beam at 7 TeV on a graphite target. It describes the optimisation of the simulation setup and the required coupling workflow. The resulting energy deposition and the evolution of the target density are discussed.

Scientific programme at the Laser Laboratory for Acceleration and Applications

In recent years, laser-driven accelerators have emerged as a promising technology for the development of compact and cost-effective sources of high-energy particles and radiation. Here, we introduce our research programme at the Laser Laboratory for Acceleration and Applications, which focusses on high-power laser systems, development of high-repetition rate targetry, and biomedical applications of laser-based accelerators. Our recent results include the generation of high-energy proton and ion beams through laser-plasma acceleration, which have potential applications in materials activation for medical imaging. We have also investigated the feasibility of using laser-driven X-rays and ion beams for radiobiological research, including FLASH therapy and hadron therapy.

Sharp dose profiles for high precision proton therapy using strongly focused proton beams

The main objective of radiotherapy is to exploit the curative potential of ionizing radiation while inflicting minimal radiation-induced damage to healthy tissue and sensitive organs. Proton beam therapy has been developed to irradiate the tumor with higher precision and dose conformity compared to conventional X-ray irradiation. The dose conformity of this treatment modality may be further improved if narrower proton beams are used. Still, this is limited by multiple Coulomb scattering of protons through tissue. The primary aim of this work was to develop techniques to produce narrow proton beams and investigate the resulting dose profiles. We introduced and assessed three different proton beam shaping techniques: (1) metal collimators (100/150 MeV), (2) focusing of conventional- (100/150 MeV), and (3) focusing of high-energy (350 MeV, shoot-through) proton beams. Focusing was governed by the initial value of the Twiss parameter alpha (alpha _0), and can be implemented with magnetic particle accelerator optics. The dose distributions in water were calculated by Monte Carlo simulations using Geant4, and evaluated by target to surface dose ratio (TSDR) in addition to the transverse beam size (sigma _T) at the target. The target was defined as the location of the Bragg peak or the focal point. The different techniques showed greatly differing dose profiles, where focusing gave pronouncedly higher relative target dose and efficient use of primary protons. Metal collimators with radii <,2~mathrm{mm} gave low TSDRs (<~0.7) and large sigma _T(>~3.6~hbox {mm}). In contrast, a focused beam of conventional (150~hbox {MeV}) energy produced a very high TSDR (>~80) with similar sigma _T as a collimated beam. High-energy focused beams were able to produce TSDRs >~100 and sigma _T around 1.5 mm. From this study, it appears very attractive to implement magnetically focused proton beams in radiotherapy of small lesions or tumors in close vicinity to healthy organs at risk. This can also lead to a paradigm change in spatially fractionated radiotherapy. Magnetic focusing would facilitate FLASH irradiation due to low losses of primary protons.