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We report the high-gradient tests results of a novel traveling wave accelerating structure for $\beta =0.3$ based on a novel approach of operating at the first negative spatial harmonic. Accelerating gradients of 50 MV/m and peak electric fields of 160 MV/m were achieved in a single structure consisting of 15 coupled cells during tests at the advanced photon source. This work was performed by RadiaBeam, in collaboration with the Argonne National Laboratory, as a part of a Research and Development Program for the development of an ultrahigh-gradient linear accelerator, the Advanced Compact Carbon Ion Linac, for hadron therapy.

In this article, we propose the conceptual design, with supporting beam dynamics results, of a normal conducting, separated-sector cyclotron with a strong-focusing field gradient designed to accelerate light ions with a charge-to-mass ratio of 1/2 up to 15–20 MeV/u. The design can support a host of applications for therapy, radiobiology, material science, and instrumentation development. The light-ion species, which can include a mixed ion beam, can be dynamically chosen to provide a range of characteristic signals appropriate for specific material identification such as special nuclear materials. A conservative baseline concept is presented which has been optimized for radioisotope production of alpha emitters and theranostic radiopharmaceuticals. The modular design is also demonstrated to be scalable in gross physical parameters by a factor of 2–3, thereby reducing the size, weight, and power requirements (SWaP) and enabling near-term security applications.

X-ray induced acoustic computed tomography (XACT) provides X-ray absorption based contrast with acoustic detection. For its clinical translation, XACT imaging often has a limited field of view. This can result in image artifacts and overall loss of quantification accuracy. In this article, we aim to demonstrate model-based XACT image reconstruction to address these problems. An efficient matrix-free implementation of the regularized LSQR (MF-LSQR) based minimization scheme and a non-iterative model back-projection (MBP) scheme for computing XACT reconstructions have been demonstrated in this paper. The proposed algorithms have been numerically validated and then employed to perform reconstructions from experimental measurements obtained from an XACT setup. While the commonly used back-projection algorithm produces limited-view and noisy artifacts in the region of interest, model-based LSQR minimization overcomes these issues. The model based algorithms also reduce the ring artifacts caused due to the non-uniformity response of the multichannel data acquisition. Using the model-based reconstruction algorithms, we are able to obtain reasonable XACT reconstructions for acoustic measurements of up to 120° view. Although the MBP is more efficient than the model-based LSQR algorithm, it provides only the structural information of the region of interest. Overall, it has been demonstrated that the model-based image reconstruction yields better image quality for XACT than the standard back-projection. Moreover, the combination of model-based image reconstruction with different regularization methods can solve the limited view problem for XACT imaging (in many realistic cases where the full-view dataset is unavailable) and hence pave the way for the future clinical translation.

The three most popular radiation oncology technologies are based on using beams of photons, electrons, and hadrons (protons and heavy ions). Photon radiotherapy is currently a quite mature and advanced technology. However, it continues to evolve toward improvement of its medical effectiveness and set new requirements for the radiation source, which is typically an electron linear accelerator (linac). For example, novel techniques that involve tumor irradiation from 4π angle or FLASH ultrafast delivery of large doses cannot be efficiently realized with the existing accelerators. At the same time, hadron radiotherapy promises improved treatment outcomes in certain cases. Efforts are underway to develop more compact hadron linac technologies with the ability to change the beam energy in millisecond time scales for efficient spot scanning. In this paper we will overview the current trends in linac technologies for electron, photon and hadron therapy, and provide examples of such developments at RadiaBeam.

RadiaBeam has developed a 6 MeV accelerator that is compact and light enough to be placed on a robotic arm or light truck. The main drivers of size and weight in conventional accelerators are the power source and the shielding. Small dimensions are enabled by operation at 9.3 GHz frequency (X-band), which allows reducing the size and weight of all accelerator components. Thanks to the robust design of the accelerating structure, the accelerator can be used as a source for novel cargo inspection and radiotherapy techniques. In this paper, we present the linac design and its components, as well the results of the experimental demonstration of beam acceleration.

Ultra-high dose rate in radiotherapy (FLASH) has been shown to increase the therapeutic index with markedly reduced normal tissue toxicity and the same or better tumor cell killing. The challenge to achieve FLASH using x-rays, besides developing a high output linac, is to intensity-modulate the high-dose-rate x-rays so that the biological gain is not offset by the lack of physical dose conformity. In this study, we develop the ROtational direct Aperture optimization with a Decoupled ring-collimator (ROAD) to achieve simultaneous ultrafast delivery and complex dose modulation. The ROAD design includes a fast-rotating slip-ring linac and a decoupled collimator-ring with 75 pre-shaped multi-leaf-collimator (MLC) modules. The ring-source rotates at 1 rotation per second (rps) clockwise while the ring-collimator is either static or rotating at 1 rps counterclockwise, achieving 75 (ROAD-75) or 150 (ROAD-150) equal-angular beams for one full arc. The Direct Aperture Optimization (DAO) for ROAD was formulated to include a least-square dose fidelity, an anisotropic total variation term, and a single segment term. The FLASH dose (FD) and FLASH biological equivalent dose (FBED) were computed voxelwise, with the latter using a spatiotemporal model accounting for radiolytic oxygen depletion. ROAD was compared with clinical volumetric modulated arc therapy (VMAT) on a brain, a lung, a prostate, and a head and neck cancer patient. The mean dose rate of ROAD-75 and ROAD-150 are 76.2 Gy s(−1) and 112 Gy s(−1) respectively to deliver 25 Gy single-fraction dose in 1 s. With improved PTV homogeneity, ROAD-150 reduced (max, mean) OAR physical dose by (4.8 Gy, 6.3 Gy). The average R50 and integral dose of (VMAT, ROAD-75, ROAD-150) are (4.8, 3.2, 3.2) and (89, 57, 56) Gy × Liter, respectively. The FD and FBED showed model dependent FLASH effects. The novel ROAD design achieves ultrafast dose delivery and improves physical dosimetry compared with clinical VMAT, providing a potentially viable engineering solution for x-ray FLASH radiotherapy.

Despite significant dosimetric gains, clinical implementation of the 4π non-coplanar radiotherapy on the widely available C-arm gantry system is hindered by limited clearance, and the need to perform complex coordinated gantry and couch motion. A robotic radiotherapy platform would be conducive to such treatment but a new conflict between field size and MLC modulation resolution needs to be managed for versatile applications. This study investigates the dosimetry and delivery efficiency of purposefully creating many isocenters to achieve simultaneously high MLC modulation resolution and large tumor coverage. An integrated optimization framework was proposed for simultaneous beam orientation optimization (BOO), isocenter selection, and fluence map optimization (FMO). The framework includes a least-square dose fidelity objective, a total variation term for regularizing the fluence smoothness, and a group sparsity term for beam selection. A minimal number of isocenters were identified for efficient target coverage. Colliding beams excluded, high-resolution small-field 4π intensity-modulated radiotherapy (IMRT) treatment plans with 50 cm source-to-isocenter distance (SID-50) on 10 Head and Neck (H&N) cancer patients were compared with low-resolution large-field plans with 100 cm SID (SID-100). With the same or better target coverage, the average reduction of [Dmean, Dmax] of 20-beam SID-50 plans from 20-beam SID-100 plans were [2.09 Gy, 1.19 Gy] for organs at risk (OARs) overall, [3.05 Gy, 0.04 Gy] for parotid gland, [3.62 Gy, 5.19 Gy] for larynx, and [3.27 Gy, 1.10 Gy] for mandible. R50 and integral dose were reduced by 5.3% and 9.6%, respectively. Wilcoxon signed-rank test showed significant difference (p

Although linear accelerators are used in many security, industrial and medical applications, the existing technologies are too large and expensive for several critical applications such as radioactive source replacement, field radiography and mobile cargo scanners. One of the main requirements for these sources is to be highly portable to allow field operation. In response to this problem, RadiaBeam has designed a hand-portable 1 MeV X-ray source, scalable to higher energies, based on Ku-band split electron linac, that can be used for Ir-192 radioisotope replacement. In this paper, we present its multiphysics and engineering design studies, as well as an accelerating structure prototype along with RF measurements.

A novel, low-dose Mobile Intelligent X-ray Inspection (MIXI) concept is being developed at RadiaBeam Technologies. The MIXI concept relies on a linac-based, adaptive, ramped energy source of short X-ray packets of pulses, a new type of fast X-ray detector, rapid processing of detector signals for intelligent control of the linac, and advanced radiography image processing. The key parameters for this system include: better than 3 mm line pair resolution; penetration greater than 320 mm of steel equivalent; scan speed with 100% image sampling rate of up to 15 km/h; and material discrimination over a range of thicknesses up to 200 mm of steel equivalent. Its minimal radiation dose, size and weight allow MIXI to be placed on a lightweight truck chassis.

This paper provides a brief overview of new screening methods that employ Modulated-Energy X-ray Pulses (MEXP) to provide a number of near-simultaneous multi-energy measurements in transmission-, backscatter-, and Computed Tomography (CT) security systems. In transmission X-ray cargo screening, these multi-energy measurements improve material discrimination, maximize penetration, and enhance contrast resolution while simultaneously reducing inspection time and dose to the environment, thus resulting in a smaller exclusion zone. In backscatter systems, the use of this method will increase penetration and improve image quality of concealed objects located deeper below the surface. Specifically, different depths within an object can be probed simultaneously. In CT, our MEXP approach mitigates the main disadvantages of the conventional dual-energy technique: a) distortion of image of the boundaries between regions with large difference in density; b) limited range of object thickness where material decomposition is valid; c) ambiguity and artifacts caused by sampling different regions due to motion of the object between interlaced pulses with distinct energies. Results of testing of the prototype of high speed Adaptive, Multi-Energy Cargo Inspection System (AMEXIS) will be presented. Progress in the development of MEXP-based backscatter inspection system, and systems for cargo screening with Adaptive CT will also be shown.

X-ray multi-energy adaptive security radiography and computed tomography inspection techniques have superior performance compared to conventional dual-energy methods where two image slices are acquired by alternating energies. This new technique allows improving the quality of radiographic and CT images, expanding the range of areal densities of the interrogated objects over which effective discrimination of materials by atomic number is possible, eliminating artifacts in the image of boundaries of different densities, and reducing the time of inspection and the required dose. For this new inspection technology, RadiaBeam Technologies is developing several new types of x-ray sources that are based on linear electron accelerators. To provide an adaptive mode of operation of inspection systems, such accelerators use fast feedback from the detector array. Depending on the application, the range of the electron energy can vary from 180 keV up to 9 MeV. In this paper, we discuss the requirements for such linear accelerators, some details about their designs, and present the results of high-power and beam testing of the S- and X- band accelerators.

RadiaBeam has developed a novel, flexible linac for electrons and X-rays (FLEX) capable of energy variation from 2 to 9 MeV within a single RF pulse. This accelerator employs a robust traveling wave accelerating structure with a large energy and power acceptance that allows the unique features of deep energy and current variation required for novel adaptive cargo inspection techniques and Computed Tomography. Robust RF and water-cooling systems allow average beam powers up to 15 kW, upgradable to 57 kW, at 6 MeV, potentially making this accelerator useful for electron beam irradiation applications. The high peak currents of the electron beam produced by FLEX enable novel FLASH radiotherapy methods with fast dose delivery. In this paper, we present the linac design and its components, as well the results of the experimental demonstration of beam acceleration with energy variation.

A tubular disk-and-ring, tapered accelerating structure for small electron linacs and MicroLinacs is considered. It consists of metal and dielectric elements inserted into a metallic tube to eliminate multi-cell, multi-step brazing. The structure enables a wide range of phase velocities (including non-relativistic), a wide bandwidth allowing large number of cells (for standing wave mode) or short filling time (for traveling wave mode), combination of compensated and purely π-mode cells, alternative periodic focusing built-in to the RF structure (the disks), and combining of RF and vacuum windows. RF and accelerating performance of such a long structure having up to four dozens cells is analyzed. Some of beam dynamics, thermal, and vacuum aspects of the structure and MicroLinac performance are considered as well.

Purpose: To deliver high quality intensity modulated radiotherapy (IMRT) using a novel generalized sparse orthogonal collimators (SOCs), the authors introduce a novel direct aperture optimization (DAO) approach based on discrete rectangular representation. Methods: A total of seven patients—two glioblastoma multiforme, three head & neck (including one with three prescription doses), and two lung—were included. 20 noncoplanar beams were selected using a column generation and pricing optimization method. The SOC is a generalized conventional orthogonal collimators with N leaves in each collimator bank, where N = 1, 2, or 4. SOC degenerates to conventional jaws when N = 1. For SOC-based IMRT, rectangular aperture optimization (RAO) was performed to optimize the fluence maps using rectangular representation, producing fluence maps that can be directly converted into a set of deliverable rectangular apertures. In order to optimize the dose distribution and minimize the number of apertures used, the overall objective was formulated to incorporate an L2 penalty reflecting the difference between the prescription and the projected doses, and an L1 sparsity regularization term to encourage a low number of nonzero rectangular basis coefficients. The optimization problem was solved using the Chambolle–Pock algorithm, a first-order primal–dual algorithm. Performance of RAO was compared to conventional two-step IMRT optimization including fluence map optimization and direct stratification for multileaf collimator (MLC) segmentation (DMS) using the same number of segments. For the RAO plans, segment travel time for SOC delivery was evaluated for the N = 1, N = 2, and N = 4 SOC designs to characterize the improvement in delivery efficiency as a function of N. Results: Comparable PTV dose homogeneity and coverage were observed between the RAO and the DMS plans. The RAO plans were slightly superior to the DMS plans in sparing critical structures. On average, the maximum and mean critical organ doses were reduced by 1.94% and 1.44% of the prescription dose. The average number of delivery segments was 12.68 segments per beam for both the RAO and DMS plans. The N = 2 and N = 4 SOC designs were, on average, 1.56 and 1.80 times more efficient than the N = 1 SOC design to deliver. The mean aperture size produced by the RAO plans was 3.9 times larger than that of the DMS plans. Conclusions: The DAO and dose domain optimization approach enabled high quality IMRT plans using a low-complexity collimator setup. The dosimetric quality is comparable or slightly superior to conventional MLC-based IMRT plans using the same number of delivery segments. The SOC IMRT delivery efficiency can be significantly improved by increasing the leaf numbers, but the number is still significantly lower than the number of leaves in a typical MLC.

A coherent, mm-sub-mm-wave source driven by a RF electron gun is proposed for wide research applications as well as auxiliary inspection and screening, safe imaging, cancer diagnostics, surface defectoscopy, and enhanced time-domain spectroscopy. It allows generation of high peak and average THz-sub-THz radiation power provided by beam pre-bunching and chirping in the RF gun followed by microbunching in magnetic compressor, and resonant Cherenkov radiation of an essentially flat beam in a robust, ∼inch-long, planar, mm-sub-mm gap structure. The proof-of-principle has been successfully demonstrated in Phase I on a 5 MeV beam of L-band thermionic injector of Idaho Accelerator Center. The system can also deliver an intense, ps-sub-ps bursts of low-to-moderate dose of relativistic electrons and X-ray radiation produced by the same beam required for pulsed radiolysis as well as to enhance screening efficiency, throughput and safety.

The development of high-gradient accelerating structures for low-$\ensuremath{\beta}$ particles is the key for compact hadron linear accelerators. A particular example of such a machine is a hadron therapy linac, which is a promising alternative to cyclic machines, traditionally used for cancer treatment. Currently, the practical utilization of linear accelerators in radiation therapy is limited by the requirement to be under 50 m in length. A usable device for cancer therapy should produce 200--250 MeV protons and/or $400--450\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$ carbon ions, which sets the requirement of having $35\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ average ``real-estate gradient'' or gradient per unit of actual accelerator length, including different accelerating sections, focusing elements and beam transport lines, and at least $50\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ accelerating gradients in the high-energy section of the linac. Such high accelerating gradients for ion linacs have recently become feasible for operations at S-band frequencies. However, the reasonable application of traditional S-band structures is practically limited to $\ensuremath{\beta}=\mathrm{v}/\mathrm{c}g0.4$. However, the simulations show that for lower phase velocities, these structures have either high surface fields ($g200\text{ }\text{ }\mathrm{MV}/\mathrm{m}$) or low shunt impedances ($l35\text{ }\text{ }\mathrm{M}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$). At the same time, a significant ($\ensuremath{\sim}10%$) reduction in the linac length can be achieved by using the $50\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ structures starting from $\ensuremath{\beta}\ensuremath{\sim}0.3$. To address this issue, we have designed a novel radio frequency structure where the beam is synchronous with the higher spatial harmonic of the electromagnetic field. In this paper, we discuss the principles of this approach, the related beam dynamics and especially the electromagnetic and thermomechanical designs of this novel structure. Besides the application to ion therapy, the technology described in this paper can be applied to future high gradient normal conducting ion linacs and high energy physics machines, such as a compact hadron collider. This approach preserves linac compactness in settings with limited space availability.

X-ray Computed Tomography (CT) is a widely used tool for security and industrial non-destructive testing (NDT). Scanned objects in these uses typically contain multiple materials with different atomic numbers. In these cases, Dual-Energy CT (DECT) has numerous advantages over conventional single-energy CT, including improved image quality, reduction of effect of scatter and other artefacts, and better material decomposition. Therefore, DECT has become the standard for inspection of objects containing multiple materials [1–2]. In this paper, we present a new CT technology: Adaptive Computed Tomography with Modulated-energy X-ray pulses (ACTM) [3]. ACTM is based on adaptive cargo radiography techniques [4–6] that have been developed over the last few years. To perform CT imaging, we propose to utilize the exact and fast Katsevich image reconstruction algorithm [7–12].Key enabling ACTM techniques are:•Linear accelerator with deep energy control.•Multi-energy spectrum in each slice provided by packets of short X-ray pulses with end-point energy ramp up (> 1 MHz rate of energy switching).•Fast detectors with reduced sensitivity to scatter radiation.•Detector readout with silicon photomultipliers (SiPM) provides time-resolved measurement of short X-ray pulses.•Electronics and an algorithm for automatic, dynamic adjustment of SiPM responsivity in detector channels provides increased dynamic range of X-ray imaging.•Real-time algorithm for X-ray pulse-by-pulse selection of high and low energy windows for dual-energy material decomposition.•Filtered Backprojection (FBP) helical image reconstruction based on the theoretically exact Katsevich algorithm.The ACTM method for dual- (or, multi-) energy CT mitigates the main disadvantages of the conventional interlaced approach:•Ambiguity and artifacts caused by sampling different regions due to motion of the object between interlaced pulses with distinct energies.•Distortion of CT image of the boundaries between regions with large difference in Z.•Small range of object thicknesses where material decomposition is valid.

The security market requirements for state-of-the-art mobile and portal radiography inspection systems include high imaging resolution (better than 5 mm line pair), penetration beyond 300 mm steel equivalent, material discrimination (three groups of Z) at speeds up to 16 km/h with 100% image sampling, low dose and small radiation exclusion zone. New research into radiography methods and systems has been actively pursued in order to achieve these challenging requirements. Recently, a significant portion of the R&D effort has been devoted to re-examining betatron based X-ray inspection systems. The advantages of the betatron-based inspection systems over conventional linac-based designs include small focal spot (which improves resolution), low weight and form-factor, a simpler control system and relatively low cost. A novel, low-dose Multi-Energy Betatron-based Cargo Inspection System, MEBCIS, presented in this paper relies on an innovative technique of extracting two X-ray pulses with lower-and higher-energies within a single betatron acceleration cycle (in contrast to conventional dual-energy betatrons with one X-ray pulse produced during separate betatron acceleration cycles). In addition to the new betatron, new types of fast X-ray Scintillation-Cherenkov detectors, rapid processing of detector signals, an adaptive detector feedback algorithm for control of the betatron, and algorithms for intelligent material discrimination are parts of the overall MEBCIS system. The key advantage of the MEBCIS concept is that the material discrimination data is acquired in a single scan line rather than two. Thus, for the same betatron pulse rate, the scan rate can be twice as fast (better throughput) or can be done with a lower dose, even without adaptive dynamic pulse adjustment. Application of these techniques will maximize material discrimination, penetration, and contrast resolution while simultaneously reducing dose to the environment, resulting in a smaller exclusion zone. Its minimal size and weight will allow MEBCIS to be placed on a lightweight truck chassis.

To deliver high quality intensity modulated radiotherapy (IMRT) using a novel generalized sparse orthogonal collimators (SOCs), the authors introduce a novel direct aperture optimization (DAO) approach based on discrete rectangular representation.A total of seven patients-two glioblastoma multiforme, three headneck (including one with three prescription doses), and two lung-were included. 20 noncoplanar beams were selected using a column generation and pricing optimization method. The SOC is a generalized conventional orthogonal collimators with N leaves in each collimator bank, where N = 1, 2, or 4. SOC degenerates to conventional jaws when N = 1. For SOC-based IMRT, rectangular aperture optimization (RAO) was performed to optimize the fluence maps using rectangular representation, producing fluence maps that can be directly converted into a set of deliverable rectangular apertures. In order to optimize the dose distribution and minimize the number of apertures used, the overall objective was formulated to incorporate an L2 penalty reflecting the difference between the prescription and the projected doses, and an L1 sparsity regularization term to encourage a low number of nonzero rectangular basis coefficients. The optimization problem was solved using the Chambolle-Pock algorithm, a first-order primal-dual algorithm. Performance of RAO was compared to conventional two-step IMRT optimization including fluence map optimization and direct stratification for multileaf collimator (MLC) segmentation (DMS) using the same number of segments. For the RAO plans, segment travel time for SOC delivery was evaluated for the N = 1, N = 2, and N = 4 SOC designs to characterize the improvement in delivery efficiency as a function of N.Comparable PTV dose homogeneity and coverage were observed between the RAO and the DMS plans. The RAO plans were slightly superior to the DMS plans in sparing critical structures. On average, the maximum and mean critical organ doses were reduced by 1.94% and 1.44% of the prescription dose. The average number of delivery segments was 12.68 segments per beam for both the RAO and DMS plans. The N = 2 and N = 4 SOC designs were, on average, 1.56 and 1.80 times more efficient than the N = 1 SOC design to deliver. The mean aperture size produced by the RAO plans was 3.9 times larger than that of the DMS plans.The DAO and dose domain optimization approach enabled high quality IMRT plans using a low-complexity collimator setup. The dosimetric quality is comparable or slightly superior to conventional MLC-based IMRT plans using the same number of delivery segments. The SOC IMRT delivery efficiency can be significantly improved by increasing the leaf numbers, but the number is still significantly lower than the number of leaves in a typical MLC.

The security market requirements for high throughput rail cargo radiography inspection systems include better than 5 mm line pair imaging resolution, penetration beyond 400 mm steel equivalent, scan speeds of up to 60 km/h, material discrimination (four groups of Z) in 100 % of cargo at speeds reaching 45 km/h, low dose and small radiation exclusioi zone. In order to achieve these requirements, which cannot be met t conventional dual energy radiography systems, a team lead by RadiaBeam Technologies, LLC (RBT) has initiated a research into new radiography methods and imaging detector materials with the goal of developing an Adaptive Railroad Cargo Inspection System (ARCIS). The ARCIS technical concept relies on linac-based, adaptive, ramped energy source of packets of short X-ray pulses sampled by a new type of fast X-ray detectors with rapid hardware processing for intelligent linac control, and advanced radiography image processing and material discrimination analysis. The following ARCIS key enabling technologies overcome the limitations of the conventional dual energy interlaced cargo inspection systems: • Multi-energy material discrimination in a single scan line provided by packets of short pulses from an X-ray source with end-point energy ramp up (> 1 MHz rate of energy switching); • Real-time intelligent setting of packet's maximum energy depend on X-ray attenuation in cargo; • Fast Scintillation-Cherenkov detectors with reduced sensitivity to scatter radiation; • Detector readout with Silicon Photomultiplier (SiPM) provides time-resolving of short X-ray pulses; • Self-control adaptive dynamic adjustment of SiPM responsivity in detector channel for increased dynamic range.

A novel high speed Adaptive Railroad Cargo Inspection System (ARCIS) is being developed at RadiaBeam Technologies. The ARCIS concept relies on linac-based, adaptive, ramped energy source of short X-ray packets of pulses, a new type of fast X-ray detectors, rapid processing of detector signals for intelligent control of the linac, and advanced radiography image processing. The requirements for this system include better than 5 mm line pair resolution, penetration greater than 400 mm of steel equivalent, scan speeds up to 60 km/h, material discrimination within 100% of image and minimal average dose. To meet these requirements a new S-band travelling wave linac with deep energy control has been designed. This paper discusses the linac design approach and its principal components, as well as engineering and manufacturing aspects.

We report observations of an intense sub-THz radiation extracted from a ∼3 MeV electron beam with a flat transverse profile propagating between two parallel oversized copper gratings with side openings. Low-loss radiation outcoupling is accomplished using a horn antenna and a miniature permanent magnet separating sub-THz and electron beams. A tabletop experiment utilizes a radio frequency thermionic electron gun delivering a thousand momentum-chirped microbunches per macropulse and an alpha-magnet with a movable beam scraper producing sub-mm microbunches. The radiated energy of tens of micro-Joules per radio frequency macropulse is demonstrated. The frequency of the radiation peak was generated and tuned across two frequency ranges: (476–584) GHz with 7% instantaneous spectrum bandwidth, and (311–334) GHz with 38% instantaneous bandwidth. This prototype setup features a robust compact source of variable frequency, narrow bandwidth sub-THz pulses.

Purpose: To develop a robust and efficient platform for the optimization and robotic delivery of highly noncoplanar intensity modulated radiotherapy, which enables significant reduction of normal tissue toxicity and escalation of tumor dose. Methods: An innovative high-output compact 3 MV linac was designed for mounting onto a commercial robotic system in order to access the entire 4π beam solution space without moving the patient couch. The use of intermediate energy X-rays for radiotherapy was evaluated in comparison to clinical plans delivered using 6 MV X-rays and a state-of-the-art delivery system. Monte Carlo simulations of a 3 MV percent depth dose curve were performed for intermediate energy dose calculation. The beam model was used to create a convolution/superposition-based dose calculation engine for 3MV X-rays. The 4π greedy column generation algorithm was used for optimized beam selection and fluence map optimization. Results: A detailed design of the first 3 MV linac capable of producing a competitively high dose rate of >800 cGy/min at 100 cm was completed and verified through extensive simulation. The complete linac head including a multileaf collimator can access most of the 4π solution space including the posterior orientations without changing the couch height. When compared to 6 MV clinical plans, the proposed 3 MV 4π plans demonstrated significantly better dose compactness and normal tissue sparing in brain, prostate, and partial breast treatment plans. Conclusion: We demonstrate the design of a highly versatile radiotherapy machine to natively deliver non-coplanar 4π radiotherapy without the need to move the patient during treatment. This novel platform is efficient and capable of providing dosimetry that is 30–50% more compact than existing therapy platforms. The new system is projected to be cost effective due to improved treatment time and automation. NIH R43CA183390, NIH R01CA188300

Special Nuclear Materials (SNM) (e.g. U-235, Pu-239) can be detected by active interrogation with gamma rays (>6 MeV) through photofission. For long-range detection (∼1 km), an intense beam of gamma rays (∼10 14 per second) is required in order to produce measurable number of neutrons. The production of such fluxes of gamma rays, and in the pulse formats useful for detection, presents many technical challenges, and requires novel approaches to the accelerator and laser technology. RadiaBeam is currently designing a gamma ray source based on Inverse Compton Scattering (ICS) from a high-energy electron beam. To achieve this, improvements in photoinjector, linac, final focus, and laser system are planned. These enhanced sub-systems build on parallel work being performed at RadiaBeam, UCLA, and elsewhere. A high-repetition rate photoinjector, a high-gradient S-band linac, and a laser pulse recirculator will be used. The proposed system will be a transportable source of high-flux, high-energy quasi-monochromatic gamma rays for active interrogation of special nuclear materials.

RadiaBeam is developing a novel linear accelerator which produces both kilovoltage (∼100 keV) X‐rays for imaging, and megavoltage (6 to 20 MeV) X‐rays for therapy. We call this system the DEXITron: Dual Energy X‐ray source for Imaging and Therapy. The Dexitron is enabled by an innovation in the electromagnetic design of the linac, which allows the output energy to be rapidly switched from high energy to low energy. In brief, the method involves switching the phase of the radiofrequency (RF) power by 180 degrees at some point in the linac such that, after that point, the linac decelerates the beam, rather than accelerating it. The Dexitron will have comparable cost to other linacs, and avoids the problems associated with current IGRT equipment.

The fixed-field alternating-gradient (FFAG) betatron has emerged as a viable alternative to RF linacs as a source of high-energy radiation for industrial and security applications. For industrial applications, high average currents at modest relativistic electron beam energies, typically in the 5 to 10 MeV range, are desired for medical product sterilization, food irradiation and materials processing. For security applications, high power X-rays in the 3 to 20 MeV range are needed for rapid screening of cargo containers and vehicles. In a FFAG betatron, high-power output is possible due to high duty factor and fast acceleration cycle: electrons are injected and accelerated in a quasi-CW mode while being confined and focused in the fixed-field alternating- gradient lattice. The beam is accelerated via magnetic induction from a betatron core made with modern low- loss magnetic materials. Here we present the design and status of a prototype FFAG betatron, called the Radiatron, as well as future prospects for these machines.

Purpose: Existing efforts to replace complex multileaf collimator (MLC) by simple jaws for intensity modulated radiation therapy (IMRT) resulted in unacceptable compromise in plan quality and delivery efficiency. We introduce a novel fluence map segmentation method based on compressed sensing for plan delivery using a simplified sparse orthogonal collimator (SOC) on the 4π non-coplanar radiotherapy platform. Methods: 4π plans with varying prescription doses were first created by automatically selecting and optimizing 20 non-coplanar beams for 2 GBM, 2 head & neck, and 2 lung patients. To create deliverable 4π plans using SOC, which are two pairs of orthogonal collimators with 1 to 4 leaves in each collimator bank, a Haar Fluence Optimization (HFO) method was used to regulate the number of Haar wavelet coefficients while maximizing the dose fidelity to the ideal prescription. The plans were directly stratified utilizing the optimized Haar wavelet rectangular basis. A matching number of deliverable segments were stratified for the MLC-based plans. Results: Compared to the MLC-based 4π plans, the SOC-based 4π plans increased the average PTV dose homogeneity from 0.811 to 0.913. PTV D98 and D99 were improved by 3.53% and 5.60% of the corresponding prescription doses. The average mean and maximal OAR doses slightly increased by 0.57% and 2.57% of the prescription doses. The average number of segments ranged between 5 and 30 per beam. The collimator travel time to create the segments decreased with increasing leaf numbers in the SOC. The two and four leaf designs were 1.71 and 1.93 times more efficient, on average, than the single leaf design. Conclusion: The innovative dose domain optimization based on compressed sensing enables uncompromised 4π non-coplanar IMRT dose delivery using simple rectangular segments that are deliverable using a sparse orthogonal collimator, which only requires 8 to 16 leaves yet is unlimited in modulation resolution. This work is supported in part by Varian Medical Systems, Inc. and NIH R43 CA18339.

We report the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in an undulator strongly tapered in period and field amplitude. The IFEL driver is a CO2 10.6 μm laser with power larger than 400 GW. The Rayleigh range of the laser, ∼ 1.8 cm, is much shorter than the undulator length so that the interaction is diffraction dominated. A few per cent of the injected particles are trapped in a stable accelerating bucket. Electrons with energies up to 35 MeV are measured by a magnetic spectrometer. Three‐dimensional simulations, in good agreement with the measured electron energy spectrum, indicate that most of the acceleration occurs in the first 25 cm of the undulator, corresponding to an energy gradient larger than 70 MeV/m. The measured energy spectrum also indicates that higher harmonic Inverse Free Electron Laser interaction takes place in the second section of the undulator.

Purpose: To investigate the feasibility of using intermediate energy 2 MV x-rays for extracranial robotic intensity modulated radiation therapy. Methods: Two megavolts flattening filter free x-rays were simulated using the Monte Carlo code MCNP (v4c). A convolution/superposition dose calculation program was tuned to match the Monte Carlo calculation. The modeled 2 MV x-rays and actual 6 MV flattened x-rays from existing Varian Linacs were used in integrated beam orientation and fluence optimization for a head and neck, a liver, a lung, and a partial breast treatment. A column generation algorithm was used for the intensity modulation and beam orientation optimization. Identical optimization parameters were applied in three different planning modes for each site: 2, 6 MV, and dual energy 2/6 MV. Results: Excellent agreement was observed between the convolution/superposition and the Monte Carlo calculated percent depth dose profiles. For the patient plans, overall, the 2/6 MV x-ray plans had the best dosimetry followed by 2 MV only and 6 MV only plans. Between the two single energy plans, the PTV coverage was equivalent but 2 MV x-rays improved organs-at-risk sparing. For the head and neck case, the 2MV plan reduced lips, mandible, tongue, oral cavity, brain, larynx, left and right parotid gland mean doses by 14%, 8%, 4%, 14%, 24%, 6%, 30% and 16%, respectively. For the liver case, the 2 MV plan reduced the liver and body mean doses by 17% and 18%, respectively. For the lung case, lung V20, V10, and V5 were reduced by 13%, 25%, and 30%, respectively. V10 of heart with 2 MV plan was reduced by 59%. For the partial breast treatment, the 2 MV plan reduced the mean dose to the ipsilateral and contralateral lungs by 27% and 47%, respectively. The mean body dose was reduced by 16%. Conclusions: The authors showed the feasibility of using flattening filter free 2 MV x-rays for extracranial treatments as evidenced by equivalent or superior dosimetry compared to 6 MV plans using the same inverse noncoplanar intensity modulated planning method.