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Trapping technologies of positrons, the antimatter counterpart of electrons, are indispensable for various atomic, molecular, and optical experiments and for material analyses that use positron swarms. Efficient trapping of high-intensity positron beams generated by electron linear accelerators (LINACs) will improve the quality and throughput rate of experiments but have yet to be practically realized. In the present work, we demonstrate the efficient trapping and extraction of a LINAC-based positron beam by using a silicon carbide (SiC) remoderator with a center hole. The positron beam was remoderated by 4H-SiC wafers in the back-reflection geometry followed by accumulation in an electromagnetic trap with CF 4 cooling gas. A rotating electric field was driven to spatially compress the accumulated positrons, enabling the lossless extraction of the positrons through the SiC hole. A trapping efficiency in the higher 20% range was achieved. The proposed trapping scheme employing a center-hole SiC remoderator is thus a practical technique to accumulate and cool positron beams generated by LINACs.

Purpose Medical linear accelerators are the most costly standard equipment used in radiation oncology, however the service costs for these machines are not well understood. With an increasing demand for linear accelerators due to a global increase in cancer incidence, it is important to understand the expected maintenance costs of a larger global installed base so that these costs can be incorporated into budgeting. The purpose of this investigation is to analyze the costs for medical linear accelerator service and maintenance at our institution, in order to estimate the service cost ratio. Methods We collected the costs of parts used for all service work done on 32 medical linear accelerators over a two year period. The data was segregated by center, machine, linear accelerator type, and failure area in the machine. Results We found the service cost ratio (excluding software support expenses) to be 3.13% [2.74%, 3.52%,]. We observed a variability of parts costs, and overall variability of the service cost ratio to be between 2.14% and 5.25%. This result is lower than other estimates for service costs for medical equipment in general and medical linear accelerators specifically. Two‐thirds of the service costs were due to labor costs, which indicate the importance of a well‐trained service technician workforce. Conclusions We estimated the service cost ratio for medical linear accelerators to be 3.13% [3.52%, 2.74%] of the initial capital cost. This result was lower than other estimates of the service cost ratio.

PurposeOsteoarthritis is a common disease, with a prevalence of symptomatic disease of 8.9%. One treatment option is radiotherapy. Most published samples were treated with an orthovoltage technique or with a telecobalt device. A lot of radiotherapy institutions are nowadays using linear accelerators for treatment of osteoarthritis. There is a discussion on whether the treatment results achieved with a linear accelerator are comparable to those with the orthovoltage technique. The aim of this study is to analyze the results of radiotherapy for osteoarthritis with a linear accelerator and compare the results with reference to different joints.Materials and MethodsThe analysis was performed in patients of two German radiotherapy institutions and included 295 irradiated joints. Pain was documented with the numeric rating scale (NRS). Evaluation of the NRS was done before and directly after each radiation therapy course as well as for the follow-up of 24 months.The median age of the patients was 65 years, with 39.0% male and 61.0% female patients. Most frequently, osteoarthritis of the knee (34.6%) or the finger (15.9%) was treated.ResultsWe could find a significant response to radiotherapy. Median pain for the whole sample was 7 on the NRS before radiotherapy, 4 after 6 weeks, and 3 after 12 and 24 months. The percentage of patients with 0 or 1 on the NRS was 33.8% 12 months after radiotherapy. All investigated subgroups had a significant reduction of pain.ConclusionRadiotherapy of osteoarthritis with a linear accelerator is an effective treatment which is very well tolerated. All analyzed subgroups show a good response to radiotherapy for at least 24 months. Orthovoltage therapy seems to be superior to treatment with a linear accelerator in a case-related analysis of the published samples. Further investigations should be performed for a definitive answer to this question.

Background The impact of beam dosimetry changes brought on by target degradation has not been well investigated. Purpose To determine the optimal dosimetry metrics for detecting target degradation and to investigate the impact of beam dosimetry changes brought on by target degradation. Methods The EGSnrc Monte Carlo programs were used to model the Varian Novalis Tx linear accelerator. By altering the central portion of the photon target with a cylindrical vacuum zone, few target degradation scenarios were simulated and compared with the nominal condition. For square photon beams defined by the jaws, the effects of target degradation on beam output, beam quality (percentage depth dose, PDD), beam profile (off‐axis factor), relative output factor (ROF), and wedge factor (WF) were examined. Few degradation scenarios were used to retroactively model the effects on patient‐specific quality assurance (PSQA). Results Under the realistic degradation conditions (0.6–0.7 mm depth, 1.0–2.0 mm widths), the 6MV beam output decreased by 5.7%–24.1% and the 30 cm field diagonal profile sag in the horns by a max deviation of 3.8%–5.9%, however, the PDD20,10 varied within 1%, and the flatness deviated by 0.74%–1.35%, respectively. As the photon target got more degraded, the beam output, beam quality and profile showed a downgrade trend from the baseline. The PDD20,10 varied from 0.7% to ‐2.8% in the 10 cm field. Before the target degraded with a 2 mm width and 0.889 mm depth hole, ROF and WF were stable (within 2% deviation). The pelvic case gamma result showed obvious decrease (90.9%) under degradation depth 0.7 mm and width 2.0 mm. Conclusion A technical approach was created and verified for precise Monte Carlo simulation of linear accelerator target degradation scenarios. The parameters with the highest sensitivity for detecting target degradation were beam output and large field diagonal profile deviation in the 0.95 field size range.

BackgroundSingle-isocenter dynamic conformal arc (SIDCA) therapy is a technically efficient way of delivering stereotactic radiosurgery (SRS) to multiple metastases simultaneously. This study reports on the safety and feasibility of linear accelerator (LINAC) based SRS with SIDCA for patients with multiple brain metastases.MethodsAll patients who received SRS with this technique between November 2017 and June 2019 within a prospective registry trial were included. The patients were irradiated with a dedicated planning tool for multiple brain metastases using a LINAC with a 5 mm multileaf collimator. Follow-up was performed every 3 months, including clinical and radiological examination with cranial magnetic resonance imaging (MRI). These early data were analyzed using descriptive statistics and the Kaplan–Meier method.ResultsA total of 65 patients with 254 lesions (range 2–12) were included in this analysis. Median beam-on time was 23 min. The median follow-up at the time of analysis was 13 months (95% CI 11.1–14.9). Median overall survival and median intracranial progression-free survival was 15 months (95% CI 7.7–22.3) and 7 months (95% CI 3.9–10.0), respectively. Intracranial and local control after 1 year was 64.6 and 97.5%, respectively. During follow-up, CTCAE grade I adverse effects (AE) were experienced by 29 patients (44.6%; 18 of them therapy related, 27.7%), CTCAE grade II AEs by four patients (6.2%; one of them therapy related, 1.5%), and CTCAE grade III by three patients (4.6%; none of them therapy related). Two lesions (0.8%) in two patients (3.1%) were histopathologically proven to be radiation necrosis.ConclusionSimultaneous SRS using SIDCA seems to be a feasible and safe treatment for patients with multiple brain metastases.

The microbunching instability in the linear accelerator (linac) of a free-electron laser facility has always been a problem that degrades the electron beam quality. In this paper, a quite simple and inexpensive technique is proposed to smooth the electron beam current profile to suppress the instability. By directly adding a short undulator with a transverse gradient field right after the injector to couple the transverse spread into the longitudinal direction, additional density mixing in the electron beam is introduced to smooth the current profile, which results in the reduction of the gain of the microbunching instability. The magnitude of the density mixing can be easily controlled by varying the strength of the undulator magnetic field. Theoretical analysis and numerical simulations demonstrate the capability of the proposed technique in the accelerator of an x-ray free-electron laser.

PurposeThis study evaluated the trends in the platform for stereotactic radiotherapy to the brain (SRT), utilizing the open data of the National Database published by the Ministry of Health, Labour, and Welfare.Materials and methodsThis study analyzed data from FY2014 to FY2021. The practices included in the study were gamma knife surgery (GKS) and SRT with a linear accelerator (LINAC). The total number of outpatient and inpatient cases in each SRT system was evaluated annually.ResultsFrom April 2014 to March 2022, the study included 212,016 cases (102,691 GKS and 109,325 LINAC) of the registered 1,996,540 radiotherapy cases. In the first year, 13,117 (54.1%) cases were GKS, and 11,128 (45.9%) were LINAC; after that, GKS decreased, and LINAC increased, reaching the same rate in FY2017. Compared to the first year, the final year showed 11,702 GKS (− 1415 or − 10.8%) and 17,169 LINAC (+ 6041 or + 54.3%), with an increase of 4626 total SRT cases to 28,871 (+ 19.1%). The percentage of outpatient treatment also increased from 4.6 to 11.8% for GKS and from 44.7 to 57.9% for LINAC.ConclusionThe study found a gradual decrease in the selection of GKS, an increasing trend in the selection of LINAC, and an increase in the overall number of stereotactic irradiations. In particular, the proportion of outpatient treatment increased, indicating that more than half of LINAC was selected for outpatient treatment.

Background Monte Carlo simulation of radiation transport for medical linear accelerators (linacs) requires accurate knowledge of the geometrical description of the linac head. Since the geometry of Varian TrueBeam machines has not been disclosed, the manufacturer distributes phase-space files of the linac patient-independent part to allow researchers to compute absorbed dose distributions using the Monte Carlo method. This approach limits the possibility of achieving an arbitrarily small statistical uncertainty. This work investigates the use of the geometry of the Varian Clinac 2100, which is included in the Monte Carlo system PRIMO, as a surrogate. Methods Energy, radial and angular distributions extracted from the TrueBeam phase space files published by the manufacturer and from phase spaces tallied with PRIMO for the Clinac 2100 were compared for the 6, 8, 10 and 15 MV flattened-filtered beams. Dose distributions in water computed for the two sets of PSFs were compared with the Varian Representative Beam Data (RBD) for square fields with sides ranging from 3 to 30 cm. Output factors were calculated for square fields with sides ranging from 2 to 40 cm. Results Excellent agreement with the RBD was obtained for the simulations that employed the phase spaces distributed by Varian as well as for those that used the surrogate geometry, reaching in both cases Gamma ( 2 % , 2 mm) pass rates larger than 99 % , except for the 15 MV surrogate. This result supports previous investigations that suggest a change in the material composition of the TrueBeam 15 MV flattening filter. In order to get the said agreement, PRIMO simulations were run using enlarged transport parameters to compensate the discrepancies between the actual and surrogate geometries. Conclusions This work sustains the claim that the simulation of the 6, 8 and 10 MV flattening-filtered beams of the TrueBeam linac can be performed using the Clinac 2100 model of PRIMO without significant loss of accuracy.

A fundamental parameter to evaluate the beam delivery precision and stability on a clinical linear accelerator (linac) is the focal spot position (FSP) measured relative to the collimator axis of the radiation head. The aims of this work were to evaluate comprehensive data on FSP acquired on linacs in clinical use and to establish the ability of alternative phantoms to detect effects on patient plan delivery related to FSP. FSP measurements were conducted using a rigid phantom holding two ball-bearings at two different distances from the radiation source. Images of these ball-bearings were acquired using the electronic portal imaging device (EPID) integrated with each linac. Machine QA was assessed using a radiation head-mounted PTW STARCHECK phantom. Patient plan QA was investigated using the SNC ArcCHECK phantom positioned on the treatment couch, irradiated with VMAT plans across a complete 360° gantry rotation and three X-ray energies. This study covered eight Elekta linacs, including those with 6 MV, 18 MV, and 6 MV flattening-filter-free (FFF) beams. The largest range in the FSP was found for 6 MV FFF. The FSP of one linac, retrofitted with 6 MV FFF, displayed substantial differences in FSP compared to 6 MV FFF beams on other linacs, which all had FSP ranges less than 0.50 mm and 0.25 mm in the lateral and longitudinal directions, respectively. The PTW STARCHECK phantom proved effective in characterising the FSP, while the SNC ArcCHECK measurements could not discern FSP-related features. Minor variations in FSP may be attributed to adjustments in linac parameters, component replacements necessary for beam delivery, and the wear and tear of various linac components, including the magnetron and gun filament. Consideration should be given to the ability of any particular phantom to detect a subsequent impact on the accuracy of patient plan delivery.