Electron beam source and switchyard design for two-energy operation of x-ray Compton sources

Object. The purpose of this work was to investigate the targeting and dosimetric characteristics of a linear accelerator (LINAC) system dedicated for stereotactic radiosurgery compared with those of a commercial gamma knife (GK) unit. Methods. A phantom was rigidly affixed within a Leksell stereotactic frame and axial computerized tomography scans were obtained using an appropriate stereotactic localization device. Treatment plans were performed, film was inserted into a recessed area, and the phantom was positioned and treated according to each treatment plan. In the case of the LINAC system, four 140° arcs, spanning ± 60° of couch rotation, were used. In the case of the GK unit, all 201 sources were left unplugged. Radiation was delivered using 3- and 8-mm LINAC collimators and 4- and 8-mm collimators of the GK unit. Targeting ability was investigated independently on the dedicated LINAC by using a primate model. Measured 50% spot widths for multisource, single-shot radiation exceeded nominal values in all cases by 38 to 70% for the GK unit and 11 to 33% for the LINAC system. Measured offsets were indicative of submillimeter targeting precision on both devices. In primate studies, the appearance of an magnetic resonance imaging—enhancing lesion coincided with the intended target. Conclusions. Radiosurgery performed using the 3-mm collimator of the dedicated LINAC exhibited characteristics that compared favorably with those of a dedicated GK unit. Overall targeting accuracy in the submillimeter range can be achieved, and dose distributions with sharp falloff can be expected for both devices.

The cyanobacterial cytochrome b(6)f complex is central for the coordination of photosynthetic and respiratory electron transport and also for the balance between linear and cyclic electron transport. The development of a purification strategy for a highly active dimeric b(6)f complex from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 enabled characterization of the structural and functional role of the small subunit PetP in this complex. Moreover, the efficient transformability of this strain allowed the generation of a ΔpetP mutant. Analysis on the whole-cell level by growth curves, photosystem II light saturation curves, and P700(+) reduction kinetics indicate a strong decrease in the linear electron transport in the mutant strain versus the wild type, while the cyclic electron transport via photosystem I and cytochrome b(6)f is largely unaffected. This reduction in linear electron transport is accompanied by a strongly decreased stability and activity of the isolated ΔpetP complex in comparison with the dimeric wild-type complex, which binds two PetP subunits. The distinct behavior of linear and cyclic electron transport may suggest the presence of two distinguishable pools of cytochrome b(6)f complexes with different functions that might be correlated with supercomplex formation.

We examined the effect of carbon metabolism inhibition, temperature, and water stress on the relationship between the linear electron transport and photosynthetic CO2 assimilation in sweet sorghum, Sorghum bicolor (L.) Moench. Carbon metabolism was inhibited either by removing CO2 from the air or by feeding glyceraldehyde to the leaves. Irrespective of the method used, the linear electron transport and photosynthesis were coordinately inhibited. However, when photosynthesis was totally inhibited, a residual electron transport between 20 and 35 µmol m-2 s-1 could be measured. The residual electron transport increased with increasing leaf temperature up to 38ºC and was higher in water-stressed leaves than in control leaves. Temperature affected photosynthesis in intact leaves. The optimal temperature for photosynthesis in control leaves was between 30 and 35ºC. The ratio between linear electron transport and photosynthesis showed a temperature dependency similar to that of photosynthesis. As a consequence, the electrons required to fix one mole of CO2 were 5.5 at suboptimal temperatures but were 6.5 at 30ºC. Our results indicate that the relationship between linear electron transport and photosynthesis is not perfectly steady in nature but is subject to transient changes. The observed changes in the linear electron transport were mostly related to changes in the efficiency of light trapping by open photosystem II (PSII) reaction centres, while the fractions of open PSII reaction centres were relatively constant during the experiment. Water stress severely reduced the photosynthetic CO2 assimilation of sweet sorghum leaves. The greater the water stress, the lower the temperature at which optimal photosynthesis was reached. The linear electron transport was coordinately inhibited by water stress but a residual electron transport was again found when photosynthesis was extremely reduced by water stress. Under water-stress conditions the fraction of PSII reaction centres in an open state was very low but constant, and the temperature dependent reduction of linear electron transport was caused by the reduction of the efficiency of energy capture of PSII reaction centres.

The geometric accuracy and precision of an image-guided treatment system were assessed. Image guidance is performed using an x-ray volume imaging (XVI) system integrated with a linear accelerator and treatment planning system. Using an amorphous silicon detector and x-ray tube, volumetric computed tomography images are reconstructed from kilovoltage radiographs by filtered backprojection. Image fusion and assessment of geometric targeting are supported by the treatment planning system. To assess the limiting accuracy and precision of image-guided treatment delivery, a rigid spherical target embedded in an opaque phantom was subjected to 21 treatment sessions over a three-month period. For each session, a volumetric data set was acquired and loaded directly into an active treatment planning session. Image fusion was used to ascertain the couch correction required to position the target at the prescribed iso-center. Corrections were validated independently using megavoltage electronic portal imaging to record the target position with respect to symmetric treatment beam apertures. An initial calibration cycle followed by repeated image-guidance sessions demonstrated the XVI system could be used to relocate an unambiguous object to within less than 1 mm of the prescribed location. Treatment could then proceed within the mechanical accuracy and precision of the delivery system. The calibration procedure maintained excellent spatial resolution and delivery precision over the duration of this study, while the linear accelerator was in routine clinical use. Based on these results, the mechanical accuracy and precision of the system are ideal for supporting high-precision localization and treatment of soft-tissue targets.

Purpose: The objective of this work is to develop an automated quality assurance (AQUA) system for linear accelerators, which will integrate multiple mechanical, dosimetric and imaging tests in a daily session of reasonable duration (30–45 min). Methods: AQUA is a web‐based application with a centralized database containing a library of quality assurance (QA) tests defined in a user‐scriptable language. AQUA communicates the test to the linear accelerator (and measuring devices) and analyzes the resulting data. The software supports concurrent testing of multiple linear accelerators. Five tests were implemented in the first AQUA prototype: Collimator and gantry rotation isocenter, radiation field‐size (multileaf collimator (MLC) and jaws), gantry angle readout and kV‐MV isocenter coincidence. Test results are obtained from the analysis of MV 2D images and cone‐beam CT datasets of a phantom setup on the treatment couch. Tests were performed on a nightly basis on one linear accelerator and elapsed time was recorded. The field‐size test reproducibility was extensively studied using simple multi‐segment beams and its accuracy was assessed using films. Results: For the first AQUA prototype which is semi‐automated, the elapsed time for the five AQUA tests was 45 min (setup, imaging and analysis). Results (n=17) for the different components tested were within institutional tolerances. The AQUA field size detection algorithm applied to 127 images of a static field showed a maximum variation in detected leaf position of ±0.15mm. AQUA was able to detect MLC positioning errors as small as 0.5mm. Field widths measured with AQUA were almost consistently smaller than with film with a maximum deviation of 0.34 mm (n=18). Conclusions: The AQUA system was developed and allows for semi‐automated and quantitative daily testing of multiple machine parameters. Work is on‐going to improve automation and efficiency and increase the number of available tests.Supported in part by Elekta Inc

The European Spallation Source (ESS) is one of Europe’s largest planned research infrastructures. The project is funded by a collaboration of 17 European countries and is under design and construction in Lund, Sweden. Three families of Superconducting Radio-Frequency (SRF) cavities are being prototyped, counting the spoke resonators with a geometric beta of 0.5, medium-beta elliptical cavities (β=0.67) and high beta elliptical cavities (β=0.86). The ESS linac will produce 2.86 ms long proton pulses with a repetition rate of 14 Hz (4 % duty cycle), a beam current of 62.5 mA and an average beam power of 5 MW. A control system is being developed to operate the different accelerator systems. All operating modes of the superconducting linac shall ensure a safe operation of the accelerator. This paper presents the preliminary functional analysis and the operating modes of the 704 MHz SRF linac.

The pre-injector of the Taiwan Light Source (TLS) is consists of a 140 kV thermionic gun and a 50 MeV travelling wave type linear accelerator (linac) system. A linac control system has been renewed to avoid obsolescence. It is also utilized to improve performance, decouple the vacuum interlock logic from the linac control system, and provide a better control functionality for top-up operation. One VME crate system is dedicated for the linac control, the new hardware equipped with high resolution of analogue interface to provide better control. Vacuum interlock logic will be done via a dedicated programmable logic controller (PLC). The remained linac devices, which are necessary for sequential control such as door access interlock, klystron warm up, gun warm up, trigger interlock, gun high voltage interlock, klystron modulator high voltage interlock, water flow interlock, will be done by another PLC. Both interlock and sequential control of PLC will be controlled by the VME crate. All of the other functions without interlock or sequence requirement will be controlled by the VME crate directly as well. New control system is expected to provide better control functionality, better performance, easy for maintenance, and useful easy to add new hardware equipments.

Background and purposeMagnetic resonance (MR)-guided linear accelerator (MR-Linac) systems have changed radiotherapy workflows. The addition of daily online contour adaptation allows for higher precision treatment, but also increases the workload of those involved. We train radiation therapists (RTTs) to perform daily online contour adaptation for MR-Linac treatment of prostate cancer (PCa) patients. The purpose of this study was to evaluate these prostate contours by performing an interfraction and interobserver analysis. Materials and methodsClinical target volume (CTV) contours generated online by RTTs from 30 low-intermediate risk PCa patients, treated with 5x7.25 Gy, were used. Two physicians (Observers) judged the RTTs contours and performed adaptations when necessary. Interfraction relative volume differences between the first and the subsequent fractions were calculated for the RTTs, Observer 1, and Observer 2. Additionally, interobserver dice’s similarity coefficient (DSC) for fraction 2–5 was calculated with the RTTs- and physician-adapted contours. Clinical acceptability of the RTTs contours was judged by a third observer. ResultsMean (SD) online contour adaptation time was 12.6 (±3.8) minutes and overall median (interquartile range [IQR]) relative volume difference was 9.3% (4.4–13.0). Adaptations by the observers were mostly performed at the apex and base of the prostate. Median (IQR) interobserver DSC between RTTs and Observer 1, RTTs and Observer 2, and Observer 1 and 2 was 0.99 (0.98–1.00), 1.00 (0.98–1.00), and 1.00 (0.99–1.00), respectively. Contours were acceptable for clinical use in 113 (94.2%) fractions. Dose-volume histogram (DVH) analysis showed significant CTV underdosage for one of the seven identified outliers. ConclusionDaily online contour adaptation by RTTs is clinically feasible for MR-Linac treatment of PCa.

PurposeTo verify the dose distribution and number of monitor units (MU) for dynamic treatment techniques like volumetric modulated single arc radiation therapy - Rapid Arc - each patient treatment plan has to be verified prior to the first treatment. The purpose of this study was to develop a patient related treatment plan verification protocol using a two dimensional ionization chamber array (MatriXX, IBA, Schwarzenbruck, Germany).MethodMeasurements were done to determine the dependence between response of 2D ionization chamber array, beam direction, and field size. Also the reproducibility of the measurements was checked. For the patient related verifications the original patient Rapid Arc treatment plan was projected on CT dataset of the MatriXX and the dose distribution was calculated. After irradiation of the Rapid Arc verification plans measured and calculated 2D dose distributions were compared using the gamma evaluation method implemented in the measuring software OmniPro (version 1.5, IBA, Schwarzenbruck, Germany).ResultsThe dependence between response of 2D ionization chamber array, field size and beam direction has shown a passing rate of 99% for field sizes between 7 cm × 7 cm and 24 cm × 24 cm for measurements of single arc. For smaller and larger field sizes than 7 cm × 7 cm and 24 cm × 24 cm the passing rate was less than 99%. The reproducibility was within a passing rate of 99% and 100%. The accuracy of the whole process including the uncertainty of the measuring system, treatment planning system, linear accelerator and isocentric laser system in the treatment room was acceptable for treatment plan verification using gamma criteria of 3% and 3 mm, 2D global gamma index.ConclusionIt was possible to verify the 2D dose distribution and MU of Rapid Arc treatment plans using the MatriXX. The use of the MatriXX for Rapid Arc treatment plan verification in clinical routine is reasonable. The passing rate should be 99% than the verification protocol is able to detect clinically significant errors.

Between 1984 and 1991 86 patients with single cerebral metastases underwent linear accelerator radiosurgery using the atraumatic and reproducible Greitz-Bergström head-fixation device. Routine one-month follow-up documented disappearance of the tumour in 16 patients, with resolution of the oedema and ventricular shift. Shrinkage of the metastasis occurred in 51 patients. In 9 patients the tumour remained stable, in 7 there was progression of tumour size. Among the patients showing shrinkage of the tumour or unchanged tumour volume, repeated radiosurgery resulted in disappearance of the metastasis in 5 and further shrinkage in 28. In 14 patients routine stereotactic CT follow-up study led to the detection of a new metastasis, again treated with excellent results. Local recurrence occurred in 2 patients and radiation necrosis in the target area in 5 patients. Radiosurgery thus proves to be an appropriate alternative to surgery. The versatility of our non-invasive and painless method permits CT staging (which we consider essential) without hospitalization of the patient.

Intensity Modulation Radiation Treatment (IMRT) technique increases significantly head leakage and the workload is also affected compared with Conventional treatment. The equivalent dose from medical Linear Accelerator (LINAC) System must be limited to prevent occupational and public exposure to radiation. Therefore, the shielding design must be adequate. The aim of this study was to reassess the shielding of our LINAC room designed for conventional treatment if we planned to treat 30% of the patients with IMRT technique at Aristide Le Dantec hospital. We propose a method to evaluate the equivalent dose by using empirical formulas from the report 151 of the National Council of Radiation Protection (NCRP151). We estimate the transmission factor for all barriers using the wall thicknesses. Equivalent doses for all surrounded areas were calculated and compared with those found during measurement. The doses observed here are below annual dose limit for occupational and public even when IMRT technique will be used for treatment of 30% of the patients in a LINAC room entirely shielded for conventional treatment. The results show also that the shielding was overestimated by at least a factor of 2. Adequacy of secondary shielding will depend on the IMRT patient workload. For conventional facilities that are being assessed for IMRT therapy, existing primary barriers will typically prove adequate. Accurate and conservative shielding design is essential for radiation protection professionals in clinical practice.

Physics design and scaling of Elise

Antimycin A (AA) is a widely used inhibitor to study photosynthesis and respiration. In photosynthesis, it is commonly used to inhibit a pathway of cyclic electron flow around photosystem I (CEF-PSI), but has also been reported to affect photosystem II (PSII), not involved in CEF-PSI. Although concerns have been raised about AA's specificity, its impact on PSII activity remains unclear. AA3 was recently proposed as a more specific inhibitor of the same CEF-PSI pathway. In the mitochondrial respiratory chain, AA inhibits complex III, like myxothiazol. Here, we investigated the direct effects of AA, AA3, and myxothiazol on PSII activity and linear photosynthetic electron transport using isolated plant PSII and thylakoid membranes. AA, but neither AA3 nor myxothiazol, directly suppressed PSII activity and linear electron transport. Furthermore, the extent of AA's effects was batch-dependent. Thus, we propose using AA3 to inhibit CEF-PSI, and myxothiazol to inhibit complex III, instead of AA.

EPICS based low-level radio frequency control system in LIPAc

RAMI analyses of the IFMIF accelerator facility and first availability allocation between systems