Momentum Acceptance Research Articles

Design of a large momentum acceptance proton therapy gantry utilizing AG-CCT magnets

Design of a large momentum acceptance proton therapy gantry utilizing AG-CCT magnets

Efficient algorithms for dynamic aperture and momentum acceptance calculation in synchrotron light sources

New algorithms useful for the calculation of dynamic aperture and momentum acceptance in circular accelerators, particularly synchrotron light sources, are developed and presented. The flood-fill tool from raster graphics inspired us to efficiently compute dynamic apertures by minimizing required trackings on stable initial coordinates, leading to several factors of speedup with respect to standard algorithms. A novel technique for momentum acceptance calculations, Fast Touschek Tracking, is developed. Thorough benchmarking using modern accelerator codes shows that the new technique can provide one or two orders of magnitude faster computation of local momentum acceptances with only limited loss of accuracy. Published by the American Physical Society 2024

Design of a large energy acceptance beamline using fixed field accelerator optics

Large energy acceptance arcs have been proposed for applications such as cancer therapy, muon accelerators, and recirculating linacs. The efficacy of hadron therapy can be improved by reducing the energy layer switching time, however this is currently limited by the small momentum acceptance of the beam delivery system (<±1%). A “closed-dispersion arc” with a large momentum acceptance has the potential to remove this bottleneck, however such a beamline has not yet been constructed. We have developed a design methodology for large momentum acceptance arcs with Fixed Field Accelerator optics, applying it to a demonstrator beam delivery system for protons at 0.5–3.0 MeV (±42% momentum acceptance) as part of the Technology for Ultra-Rapid Beam Operation project at the University of Melbourne. Using realistic magnetic fields, a beamline has been designed with zero dispersion at either end. An algorithm has been devised for the construction of permanent magnet Halbach arrays for this beamline with multipole error below one part in 104, using commercially available magnets. The sensitivity to errors has been investigated, finding that the delivered beam is robust in realistic conditions. This study demonstrates that a closed-dispersion arc with fixed fields can achieve a large momentum acceptance, and we outline future work required to develop these ideas into a complete proof-of-principle beam delivery system that can be scaled up for a medical facility. Published by the American Physical Society 2024

Dose estimation using in-beam positron emission tomography: Demonstration for 11C and 15O ion beams

Ion therapy has been well established for many decades owing to sharp depth-dose gradient and high cell-killing capability of ions. However, monitoring of the incident ions is needed to reduce ion range uncertainty for effective tumor treatment. Positron-emitting ion beams, known as radioactive ion (RI) beams, can be used as the optimal clinical approach for simultaneously treating and monitoring the incident ions using positron emission tomography (PET) imaging. The low intensity of RI beams, which previously was the main difficulty of their clinical use, was recently addressed by the development of accelerator technology. Since the quantity of interest in ion therapy is the dose and a direct comparison of planned and delivered doses is highly desirable, we focused on predicting the depth dose from PET images for RI beams in this work for the first time. We developed a method for predicting the depth dose of polyenergetic ion beams of 11C and 15O from PET images of these ion beams. The depth dose in water was measured for mono- and polyenergetic ion beams. The monoenergetic ion beams had a momentum acceptance (MA) of ±0.25%, while the polyenergetic beams had an MA of ±2.5%. PET imaging was performed during and shortly after irradiation of a polymethylmethacrylate (PMMA) phantom with mono- and polyenergetic radioactive ion beams. The energy distribution of each polyenergetic ion beam was obtained from the measured momentum distribution of that beam. A set of depth dose and PET profiles in PMMA was constructed for several monoenergetic ion beams using measured data of a monoenergetic ion beam and the range-energy relation. To estimate the depth dose for each polyenergetic beam, a linear combination of weighted PET profiles of monoenergetic beams was iteratively fitted to the measured PET profile of the polyenergetic beam, and the resulting weights were combined with the corresponding monoenergetic depth doses to predict the depth dose distribution. Significance. The depth doses of the polyenergetic ion beams were predicted with mean relative errors of 2.20% and 1.95% for 11C and 15O ion beams, respectively. These errors represent the mean value of the differences between the predicted and measured values, normalized to the maximum measured value. The predicted distal fall-off positions at 80% of the Bragg peak were within 0.13 mm of the measured values for both ion beams. The applicability of the method was demonstrated for a head phantom irradiated with 11C ion beams using Monte Carlo simulation and the predicted distal fall-off positions at 80% of the Bragg peak was within 0.08 mm of the simulated values.

Plastic scintillator fiber detectors for heavy ion trajectory reconstruction for the Super-FRS at FAIR

At the FAIR facility, currently under construction at GSI (Darmstadt), a 1.5 AGeV uranium beam with intensities up to 2.5 × 1011 238U/spill will impinge on a graphite target at the entrance of the Super-FRS for the production of a wide range of rare isotopes by projectile fission and fragmentation. The next generation in-flight magnetic separator Super-FRS, operated up to a magnetic rigidity of 20 Tm with a large angular acceptance (Δθ = ± 40 mrad, Δϕ = ± 20 mrad) and momentum acceptance (Δ p/p = ± 2.5%), requires a new generation of tracking detectors with a position resolution of 0.2 mm (σx ) over large detector areas reaching up to 570 cm2. Besides gas detectors, planar detectors made of scintillating fibers are an option worth investigating not only because of the comparable material budget but especially for the fast response and high-rate capability. A one-dimensional prototype consisting of 128 fibers with active area of 25.6 × 100 mm2 coupled to Multi-Pixel-Photon Counters (MPPCs) and readout by FPGA TDC is described together with some recent 197Au beam test results.

Mixed-size spot scanning with a compact large momentum acceptance superconducting (LMA-SC) gantry beamline for proton therapy

Objective. Lowering treatment costs and improving treatment quality are two primary goals for next-generation proton therapy (PT) facilities. This work will design a compact large momentum acceptance superconducting (LMA-SC) gantry beamline to reduce the footprint and expense of the PT facilities, with a novel mixed-size spot scanning method to improve the sparing of organs at risk (OAR). Approach. For the LMA-SC gantry beamline, the movable energy slit is placed in the middle of the last achromatic bending section, and the beam momentum spread of delivered spots can be easily changed during the treatment. Simultaneously, changing the collimator size can provide spots with various lateral spot sizes. Based on the provided large-size and small-size spot models, the treatment planning with mixed spot scanning is optimized: the interior of the target is irradiated with large-size spots (to cover the uniform-dose interior efficiently), while the peripheral of the target is irradiated with small-size spots (to shape the sharp dose falloff at the peripheral accurately). Main results. The treatment plan with mixed-size spot scanning was evaluated and compared with small and large-size spot scanning for thirteen clinical prostate cases. The mixed-size spot plan had superior target dose homogeneities, better protection of OAR, and better plan robustness than the large-size spot plan. Compared to the small-size spot plan, the mixed-size spot plan had comparable plan quality, better plan robustness, and reduced plan delivery time from 65.9 to 40.0 s. Significance. The compact LMA-SC gantry beamline is proposed with mixed-size spot scanning, with demonstrated footprint reduction and improved plan quality compared to the conventional spot scanning method.

Organic Farming in Vegetable Crops: Challenges and Opportunities

In recent times, organic farming has assumed greater significance and become a buzzword, gaining momentum and instant acceptance by producers and consumers simultaneously. Rising health complications due to the overuse of different agricultural chemicals and their consequent presence as residues above maximum permitted residue levels in food (MRLs) has bolstered the demand for a renewed emphasis on organic farming, particularly in vegetables due to the very short possible withholding period before their consumption after harvest. Vegetables are highly perishable in nature and indispensable in regular consumption. Even as the practice of organic farming is indeed very attractive in terms of nutritional and edible quality of vegetables, prevention of diseases in humans, maintenance of soil biology in diversity, population, activity levels, and preservation of soil health, it still raises queries as to whether the crops can be managed in the field without using any inorganic fertilizers or pesticides in a sustainable way over a longer period of time without affecting yields. As the challenge remains to feed the burgeoning population, it is important to ponder upon the current status, challenges, modalities, certification and prospects presented by organic cultivation of vegetable crops.

Heavy Ion Injection of Fixed-Field Alternating Gradient Accelerator

Abstract Much research in recent years has focused on circular accelerators that accelerate and store secondary particles with a large momentum spread, such as muons, unstable nuclei, and heavy ions with different charge states. A fixed-field alternating gradient (FFAG) accelerator with large transverse and momentum acceptance has obvious advantages for such requirements. A versatile beam injection method is required to accelerate secondary particles with a large momentum spread and different charge states with an FFAG accelerator. In the present study, a method for charge exchange injection of positive heavy ions using the large momentum acceptance of an FFAG accelerator is proposed. A charge injection system, which converts a He1+ beam to a He2+ beam, is developed for a 150 MeV FFAG accelerator at the Center for Accelerator and Beam Applied Science (CABAS) of Kyushu University. As the first step to verify the injection method, an orbit shift from one charge state to the other is demonstrated. This is the first demonstration of heavy ion injection using an FFAG accelerator.

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.

Progress Toward TURBO: A Novel Beam Delivery System for Charged Particle Therapy

TURBO – Technology for Ultra Rapid Beam Operation – is a novel beam delivery system (BDS) in development at the University of Melbourne. The BDS determines several aspects of treatment delivery where a key bottleneck is the deadtime associated with beam energy variation. Beamlines at treatment facilities have a ±1% momentum acceptance range, requiring all the magnetic fields to adjust to deliver different energy beams at multiple depths in the tumour volume. A BDS using Fixed Field Alternating Gradient (FFA) optics could reduce the energy layer switching time (ELST) by enabling the transport of a large range of beam energies within the same fixed fields. We present recent progress and ongoing developments with TURBO, a proof-of-concept demonstrator adapted for low energy protons. Characterisation measurements were performed to determine realistic parameters for beam transport and particle tracking modelling. Simulation and experimental studies are shown for an energy degrader. We mention considerations of canted-cosine-theta magnets and further work to explore the clinical feasibility of a scaled-up BDS for charged particle therapy.

The solenoidal large intensity device (SoLID) for JLab 12 GeV

The solenoidal large intensity device (SoLID) is a new experimental apparatus planned for Hall A at the Thomas Jefferson National Accelerator Facility (JLab). SoLID will combine large angular and momentum acceptance with the capability to handle very high data rates at high luminosity. With a slate of approved high-impact physics experiments, SoLID will push JLab to a new limit at the QCD intensity frontier that will exploit the full potential of its 12 GeV electron beam. In this paper, we present an overview of the rich physics program that can be realized with SoLID, which encompasses the tomography of the nucleon in 3D momentum space from semi-inclusive deep inelastic scattering, expanding the phase space in the search for new physics and novel hadronic effects in parity-violating DIS, a precision measurement of J/ψ production at threshold that probes the gluon field and its contribution to the proton mass, tomography of the nucleon in combined coordinate and momentum space with deep exclusive reactions, and more. To meet the challenging requirements, the design of SoLID described here takes full advantage of recent progress in detector, data acquisition and computing technologies. In addition, we outline potential experiments beyond the currently approved program and discuss the physics that could be explored should upgrades of CEBAF become a reality in the future.

Exploring beamline momentum acceptance for tracking respiratory variability in lung cancer proton therapy: a simulation study

Objective. Investigating the aspects of proton beam delivery to track organ motion with pencil beam scanning therapy. Considering current systems as a reference, specify requirements for next-generation units aiming at real-time image-guided treatments. Approach. Proton treatments for six non-small cell lung cancer (NSCLC) patients were simulated using repeated 4DCTs to model respiratory motion variability. Energy corrections required for this treatment site were evaluated for different approaches to tumour tracking, focusing on the potential for energy adjustment within beamline momentum acceptance (dp/p). A respiration-synchronised tracking, taking into account realistic machine delivery limits, was compared to ideal tracking scenarios, in which unconstrained energy corrections are possible. Rescanning and the use of multiple fields to mitigate residual interplay effects and dose degradation have also been investigated. Main results. Energy correction requirements increased with motion amplitudes, for all patients and tracking scenarios. Higher dose degradation was found for larger motion amplitudes, rescanning has beneficial effects and helped to improve dosimetry metrics for the investigated limited dp/p of 1.2% (realistic) and 2.4%. The median differences between ideal and respiratory-synchronised tracking show minimal discrepancies, 1% and 5% respectively for dose coverage (CTV V95) and homogeneity (D5-D95). Multiple-field planning improves D5-D95 up to 50% in the most extreme cases while it does not show a significant effect on V95. Significance. This work shows the potential of implementing tumour tracking in current proton therapy units and outlines design requirements for future developments. Energy regulation within momentum acceptance was investigated to tracking tumour motion with respiratory-synchronisation, achieving results in line with the performance of ideal tracking scenarios. ±5% Δp/p would allow to compensate for all range offsets in our NSCLC patient cohort, including breathing variability. However, the realistic momentum of 1.2% dp/p representative of existing medical units limitations, has been shown to preserve plan quality.

Fast trajectory reconstruction techniques for the large acceptance magnetic spectrometer VAMOS++

The large angular and momentum acceptance magnetic spectrometer VAMOS++, at GANIL, France, is frequently used for nuclear structure and reaction dynamics studies. It provides an event-by-event identification of heavy ions produced in nuclear reactions at beam energies around the Coulomb barrier. The highly non-linear ion optics of VAMOS++ requires the use of the heavy ion trajectory reconstruction methods in the spectrometer to obtain the high-resolution definition of the measured atomic mass number. Three different trajectory reconstruction methods, developed and used for VAMOS++, are presented in this work. The performances obtained, in terms of resolution of reconstructed atomic mass number, are demonstrated and discussed using a single data-set of fission fragments detected in the spectrometer.

Effects of nonvanishing net charge on balance functions and their integrals

We investigate the impact of non-vanishing net-charge in collision systems on measurements of balance functions and their integrals. We show that the nominal balance function definition yields integrals that deviate from unity because of the non-vanishing net-charge. However, the integral of unified balance functions is shown to appropriately converge to unity when measured in a sufficiently wide experimental acceptance. We furthermore explore the rate of convergence of unified balance functions integrals and study distortions imparted on the shape of balance functions when measurements are carried out in limited transverse momentum ($p_{\rm T}$) and rapidity ($y$) acceptances, such as those featured by experiments at the Large Hadron Collider or the Relativistic Heavy Ion Collider. We show that the shape and integral of unified balance functions may be strongly biased by reductions in the rapidity and transverse momentum acceptances of existing experiments.

Improving delivery efficiency using spots and energy layers reduction algorithms based on a large momentum acceptance beamline.

Intensity-modulated proton therapy (IMPT) is a well-known delivery method of proton therapy. Besides higher plan quality, reducing the delivery time is also essential to IMPT plans. It can enhance patient comfort, reduce treatment costs, and improve delivery efficiency. From the perspective of treatment efficacy, it contributes to mitigating the intra-fractional motions and improving the accuracy of radiotherapy, especially for moving tumors. However, there is a tradeoff problem between the plan quality and delivery time. We consider the potential of a large momentum acceptance (LMA) beamline and apply the spots and energy layers reduction method to reduce the delivery time. The delivery time for each field consists of the energy layer switching time, spot traveling time, and dose delivery time. The larger momentum spread and higher intensity beam offered by the LMA beamline contribute to reducing the total delivery time compared to the conventional beamline. In addition to the dose fidelity term, an L1 and logarithm items were added to the objective function to increase the sparsity of the low-weighted spots and energy layers. After that, the low-weighted spots and layers were iteratively excluded in the reduced plan, which reduced the energy layer switching time and spot traveling time. We used the standard, reduced, and LMA-reduced plans to validate the proposed method and tested it on prostate and nasopharyngeal cases. Then, we compared and evaluated the plan quality, treatment time, and plan robustness against delivery uncertainty. Compared with the standard plans, the number of spots in the LMA-reduced plans was on average reduced by 13 400 (95.6%) for prostate cases and by 48 300 (80.7%) for nasopharyngeal cases and the number of energy layers was on average reduced by 49 (61.3%) for prostate cases and by 97 (50.5%) for nasopharyngeal cases. And, the delivery time of the LMA-reduced plans was shortened from 34.5 to 8.6 s for prostate cases and from 163.8 to 53.6 s for nasopharyngeal cases. The LMA-reduced plans had comparable robustness to the spot monitor unit (MU) error compared with the standard plans, but the LMA-reduced plans became more sensitive to spot position uncertainty. The delivery efficiency can be significantly improved using the LMA beamline and spots and energy layers reduction strategies. The method is promising to improve the efficiency of motion mitigation strategies for treating moving tumors.

Optical design and higher-order aberrations with the superconducting gantry based on limited ramping fields

One of the major challenges in proton therapy is the cost and scale of the treatment facility, which depends mainly on the dimensions of the gantry. A potential method that promises to make the gantry lighter and more compact is superconducting magnet technology. However, the rapid ramping requirements during energy modulation are the primary reason for magnet quenching. To alleviate these restrictions, we propose a superconducting bending section consisting of a TBA lattice for a gantry optical design. With only three magnetic field settings needed to deliver 70–200 MeV proton beams, it achieves ±10% large momentum acceptance owing to its significant dispersion function suppression capabilities. Another feature that contributes to reducing the footprint is the installation of a degrader on the proposed gantry, allowing the degraded beam to be guided directly to the isocenter without being filtered by the Energy Selection System. For verifying the feasibility of the concept, we assess the possibility of beam scraping in the beam path and beam spot distortion at the isocenter. These efforts are accomplished by modeling realistic field distributions with ANSYS Maxwell and then performing 7th-order transfer mapping through COSY Infinity. Regarding the influence of broad energy spread on beam depth dose distribution, TOPAS is used to simulate and compare the integrated depth dose for various therapeutic energies.

Beam optics studies for a novel gantry for hadron therapy

The design of smaller and less costly gantries for carbon ion particle therapy represents a major challenge to the diffusion of this treatment. Here we present the work done on the linear beam optics of possible gantry layouts, differing for geometry, momentum acceptance, and magnet technology, which share the use of combined function superconducting magnets with a bending field of 4 T. We performed parallel– to–point and point–to–point optics matching at different magnification factors to provide two different beam sizes at the isocenter. Moreover, we considered the orbit distortion generated by magnet errors and we introduced beam position monitors and correctors. The study, together with considerations on the criteria for comparison, is the basis for the design of a novel and compact gantry for hadrontherapy.

Reconstruction and beam-transport study of the cERL dump line for high-power IR-FEL operation

Infrared (IR) SASE-FEL emission was successfully generated for macro pulses of about 1 μs with the maximum repetition rate of 5 Hz at the cERL. In the future, high-power FEL operation will be planned to increase electron bunches drastically with energy recovery. Therefore, the dump line was redesigned and reconstructed to increase the momentum acceptance and to improve the magnet system for avoiding serious beam loss in the high power FEL operation. Furthermore, the first beam-transport study was performed by transporting the beam directly from the injector to the beam dump through the reconstructed dump line. In this paper, we present the reconstructed dump line and the beam-transport study. The new dump line can be a model for dump lines of high-power ERL-FELs.

TURBO: A novel beam delivery system enabling rapid depth scanning for charged particle therapy

Charged particle therapy (CPT) is a well-established modality of cancer treatment and is increasing in worldwide presence due to improved accelerator technology and modern techniques. The beam delivery system (BDS) determines the overall timing and beam shaping capabilities, but is restricted by the energy variation speed: energy layer switching time (ELST). Existing treatment beamlines have a ±1% momentum acceptance range, needing time to change the magnetic fields as the beam is delivered in layers at various depths across the tumour volume. Minimising the ELST can enable the delivery of faster, more effective and advanced treatments but requires an improved BDS. A possibility for this could be achieved with a design using Fixed Field Alternating Gradient (FFA) optics, enabling a large energy acceptance to rapidly transport beams of varying energies. A scaled-down, novel system – Technology for Ultra Rapid Beam Operation (TURBO) – is being developed at the University of Melbourne, to explore the potential of rapid depth scanning. Initial simulation studies, beam and field measurements, project plans and clinical considerations are discussed.

Online optimisation of the MAX IV 3 GeV storage ring octupoles

The MAX IV 3 GeV storage ring lattice contains three separate families of octupole magnets. During the lattice design, they served the purpose of minimising the amplitude-dependent tune shift. Ensuring the optimal settings of the octupoles is important in order to achieve the desired machine performance in terms of transverse dynamic acceptance and momentum acceptance. This paper describes the online optimisation process used to find octupole settings which improve the Touschek lifetime, and better recreate the desired amplitude-dependent tune shift, as well as their effect on transverse dynamic acceptance and momentum acceptance.