Minibeam Collimator Research Articles

Monitoring electron and proton beam profiles with segmented silicon sensors

The FRIDA INFN project characterized thin silicon sensors for monitoring electron FLASH beams, showing a response linearity up to ∼10 Gy/pulse on 9 MeV electrons. The use of segmented silicon configurations could provide the spatial resolution useful in Spatially Fractionated Radiotherapy (SFRT). Within the MIRO INFN project, a strip sensor integrated with a multichannel readout chip is being developed and tested for monitoring FLASH and SFRT electron and proton beams. One hundred and twenty-eight strips are independently read by two front-end TERA chips. Preliminary tests were performed on 6–10 MeV electron beams at the LINAC at Physics Department of the University of Torino, with and without using a tungsten minibeam collimator, and on 62–226 MeV proton beams at CNAO (Pavia). The capability to spatially resolve electron and proton beams at conventional dose-rates has been proved.

Preclinical photon minibeam radiotherapy using a custom collimator: Dosimetry characterization and preliminary in-vivo results on a glioma model

PurposeThe purpose of this study is to investigate the dosimetric characteristics of a collimator for minibeam radiotherapy (MBRT) with film dosimetry and Monte Carlo (MC) simulations. The outcome of MBRT with respect to conventional RT using a glioma preclinical model was also evaluated. MethodsA multi-slit collimator was designed to be used with commercial small animal irradiator. The collimator was built by aligning 0.6 mm wide and 5 mm thick parallel lead leaves at 0.4 mm intervals. Dosimetry characteristics were evaluated by Gafchromic (CG) films and TOPAS Monte Carlo (MC) code.An in vivo experiment was performed using a glioma preclinical model by injecting two million GL261cells subcutaneously and treating with 25 Gy, single fraction, with MBRT and conventional RT. Survival curves and acute radiation damage were measured to compare both treatments. ResultsA satisfactory agreement between experimental results and MC simulations were obtained, the measured FWHM and distance between the peaks were respectively 0.431 and 1.098 mm.In vivo results show that MBRT can provide local tumor control for three weeks after RT treatment and a similar survival fraction of open beam radiotherapy. No severe acute effects were seen for the MBRT group. ConclusionsWe developed a minibeam collimator and presented its dosimetric features. Satisfactory agreement between MC and GC films was found with differences consistent with uncertainties due to fabrication and set-up errors. The survival curves of MBRT and open field RT are similar while atoxicity is dramatically lower with MBRT, preliminarily confirming the expected effect.

Design and characterisation of a minibeam collimator utilising Monte Carlo simulation and a clinical linear accelerator

Objective. Spatially fractionated radiotherapy is showing promise as a treatment modality. Initial focus was on beams of photons at low energy produced from a synchrotron but more recently research has expanded to include applications in proton therapy. Interest in photon beams remains and this is the focus of this paper Approach. This study presents a 3D printed tungsten minibeam collimator intended to produce peak-to-valley dose ratios (PVDR) of between seven and ten with a 1 MV, bremsstrahlung generated, photon beam. The design of the collimator is motivated by a Monte Carlo study estimating the PVDR for different collimator designs at different energies. This collimator was characterised on a clinical linear accelerator (Elekta VersaHD) as well as an orthovoltage unit. Main results. The performance of the fabricated collimator was measured on Elekta VersaHD running in unflattened mode with a 6 MV beam. On the Elekta VersaHD units the PVDR was measured to be between approximately 1.5 and 2.0 at 3 cm deep. For measurements with the orthovoltage unit PVDRs of greater than 10 were observed at a depth of 4 cm. Significance. The results confirmed that the predictions from simulation could be reproduced on linear accelerators currently in clinical usage, producing PVDRs between 2–2.5. Using the model to predict PVDRs using 1 MV photon beams, the threshold considered to produce enhanced normal tissue dose tolerance ( > 7) was surpassed. This suggests the possibility of using such techniques with versions of existing Linac technology which have been modified to operate at low energy and high beam currents.

Dosimetric study for breathing-induced motion effects in an abdominal pancreas phantom for carbon ion mini-beam radiotherapy.

Particle mini-beam therapy exhibits promise in sparing healthy tissue through spatial fractionation, particularly notable for heavy ions, further enhancing the already favorable differential biological effectiveness at both target and entrance regions. However, breathing-induced organ motion affects particle mini-beam irradiation schemes since the organ displacements exceed the mini-beam structure dimensions, decreasing the advantages of spatialfractionation. In this study, the impact of breathing-induced organ motion on the dose distribution was examined at the target and organs at risk(OARs) during carbon ion mini-beam irradiation for pancreaticcancer. As a first step, the carbon ion mini-beam pattern was characterized with Monte Carlo simulations. To analyze the impact of breathing-induced organ motion on the dose distribution of a virtual pancreas tumor as target and related OARs, the anthropomorphic Pancreas Phantom for Ion beam Therapy (PPIeT) was irradiated with carbon ions. A mini-beam collimator was used to deliver a spatially fractionated dose distribution. During irradiation, varying breathing motion amplitudes were induced, ranging from 5to 15mm. Post-irradiation, the 2D dose pattern was analyzed, focusing on the full width at half maximum (FWHM), center-to-center distance (ctc), and the peak-to-valley dose ratio (PVDR). The mini-beam pattern was visible within OARs, while in the virtual pancreas tumor a more homogeneous dose distribution was achieved. Applied motion affected the mini-beam pattern within the kidney, one of the OARs, reducing the PVDR from 3.78 0.12 to 1.478 0.070 for the 15mm motion amplitude. In the immobile OARs including the spine and the skin at the back, the PVDR did not change within 3.4% comparing reference and motionconditions. This study provides an initial understanding of how breathing-induced organ motion affects spatial fractionation during carbon ion irradiation, using an anthropomorphic phantom. A decrease in the PVDR was observed in the right kidney when breathing-induced motion was applied, potentially increasing the risk of damage to OARs. Therefore, further studies are needed to explore the clinical viability of mini-beam radiotherapy with carbon ions when irradiating abdominalregions.

PMBRT: Principles and Design of Advanced Proton Radiotherapy Techniques

The development history of pMBRT, the biological role of minibeam, the mechanism of minibeam protection of tissues, the generation of minibeam (collimator method and magnetic focusing method), and the analysis of advantages and disadvantages of proton minibeam matrix arrays is introduced with advanced proton minibeam arrays (pMBRT). It is proposed that the combination of proton minibeam arrays and magnetic resonance fields can help to exploit the normal tissue protective function of pMBRT, and improve the precision of proton therapy.

Comprehensive dosimetric commissioning of proton minibeam radiotherapy on a single gantry proton system.

Proton minibeam radiation therapy (pMBRT) can deliver spatially fractionated dose distributions with submillimeter resolution. These dose distributions exhibit significant heterogeneity in both depth and lateral directions. Accurate characterization of pMBRT doses requires dosimetry devices with high spatial resolution and a wide dynamic range. Furthermore, the dependency of dosimetric measurements on Linear Energy Transfer (LET), as observed in conventional proton therapy, is also present in pMBRT depth dose measurements. This work demonstrates the process of performing comprehensive dosimetric measurements to characterize the pMBRT collimator on a clinical single-gantry proton machine, utilizing commercially available dosimetry devices. The minibeam collimator is designed to be mounted on the clinical nozzle as a beam-modifying accessory. Three collimators, each with a slit opening of 0.4 mm, are thoroughly evaluated. The center-to-center (c-t-c) distances of the slits for these collimators are 2.8 mm, 3.2 mm, and 4.0 mm, respectively. High spatial resolution dosimetry devices are essential for PMBRT dose characterizations. To meet this requirement, two-dimensional (2D) dose measurement devices, Gafchromic films, are used to measure lateral profiles at various depths. Films are also used for depth dose profile measurements in solid water. Additionally, high-resolution point dose detectors, microDiamond, and Razor diode detectors are employed for lateral profile measurements at various depths. Percent depth dose (PDD) measurements of pMBRT in solid water, with various proton energies, collimators, and air gaps, are performed using Gafchromic films. The film's LET dependency for proton beams is corrected to ensure accurate pMBRT PDD measurements. The Monte Carlo simulation tool TOPAS is utilized to compare and validate all experimental measurements. At depths where LET is not a concern, film dose measurements were consistent with microDiamond and Razor diode point measurements. The point detectors need to be orientated with the thin side aligned to the incoming beam. Comparison of the lateral dose profiles extracted from TOPAS simulations, films, microDiamond, and Razor diode detectors shows a passing rate exceeding 98% in 1D gamma analysis at 3% 0.1 mm criteria.However, when the microDiamond detector is orientated to face the pMBRT beam, its spatial resolution may not be sufficient to capture the peak and valley dose accurately. Nevertheless, an accuracy within 2% can still be achieved when comparing the average dose. The PDD measurements show that the peak valley dose ratio (PVDR) of pMBRT can be altered at different depths with different air gaps using the same collimator or different collimators of different c-t-c distances. Our study demonstrates that comprehensive dose measurements for pMBRT can be conducted using standard clinical dose measurement devices. These measurements are indispensable for guiding and ensuring accurate dose reporting in pre-clinical studies using the pMBRT technique.

Investigating Slit-Collimator-Produced Carbon Ion Minibeams with High-Resolution CMOS Sensors

Particle minibeam therapy has demonstrated the potential for better healthy tissue sparing due to spatial fractionation of the delivered dose. Especially for heavy ions, the spatial fractionation could enhance the already favorable differential biological effectiveness at the target and the entrance region. Moreover, spatial fractionation could even be a viable option for bringing ions heavier than carbon back into patient application. To understand the effect of minibeam therapy, however, requires careful conduction of pre-clinical experiments, for which precise knowledge of the minibeam characteristics is crucial. This work introduces the use of high-spatial-resolution CMOS sensors to characterize collimator-produced carbon ion minibeams in terms of lateral fluence distribution, secondary fragments, track-averaged linear energy transfer distribution, and collimator alignment. Additional simulations were performed to further analyze the parameter space of the carbon ion minibeams in terms of beam characteristics, collimator positioning, and collimator manufacturing accuracy. Finally, a new concept for reducing the neutron dose to the patient by means of an additional neutron shield added to the collimator setup is proposed and validated in simulation. The carbon ion minibeam collimator characterized in this work is used in ongoing pre-clinical experiments on heavy ion minibeam therapy at the GSI.

Development and characterization of a versatile mini-beam collimator for pre-clinical photon beam irradiation.

Interest in spatial fractionation radiotherapy has exponentially increased over the last decade as a significant reduction of healthy tissue toxicity was observed by mini-beam irradiation. Published studies, however, mostly use rigid mini-beam collimators dedicated to their exact experimental arrangement such that changing the setup or testing new mini-beam collimator configurations becomes challenging andexpensive. In this work, a versatile, low-cost mini-beam collimator was designed and manufactured for pre-clinical applications with X-ray beams. The mini-beam collimator enables variability of the full width at half maximum (FWHM), the center-to-center distance (ctc), the peak-to-valley dose ratio (PVDR), and the source-to-collimator distance (SCD). The mini-beam collimator is an in-house development, which was constructed of 10× 40mm2 tungsten or brass plates. These metal plates were combined with 3D-printed plastic plates that can be stacked together in the desired order. A standard X-ray source was used for the dosimetric characterization of four different configurations of the collimator, including a combination of plastic plates of 0.5, 1, or 2mm width, assembled with 1 or 2mm thick metal plates. Irradiations were done at three different SCDs for characterizing the performance of the collimator. For the SCDs closer to the radiation source, the plastic plates were 3D-printed with a dedicated angle to compensate for the X-ray beam divergence, making it possible to study ultra-high dose rates of around 40Gy/s. All dosimetric quantifications were performed using EBT-XD films. Additionally, in vitro studies with H460 cells were carriedout. Characteristic mini-beam dose distributions were obtained with the developed collimator using a conventional X-ray source. With the exchangeable 3D-printed plates, FWHM and ctc from 0.52 to 2.11mm, and from 1.77 to 4.61mm were achieved, with uncertainties ranging from 0.01% to 8.98%, respectively. The FWHM and ctc obtained with the EBT-XD films are in agreement with the design of each mini-beam collimator configuration. For dose rates in the order of several Gy/min, the highest PVDR of 10.09 ± 1.08 was achieved with a collimator configuration of 0.5mm thick plastic plates and 2mm thick metal plates. Exchanging the tungsten plates with the lower-density metal brass reduced the PVDR by approximately 50%. Also, increasing the dose rate to ultra-high dose rates was feasible with the mini-beam collimator, where a PVDR of 24.26 ± 2.10 was achieved. Finally, it was possible to deliver and quantify mini-beam dose distribution patterns in vitro. With the developed collimator, we achieved various mini-beam dose distributions that can be adjusted according to the needs of the user in regards to FWHM, ctc, PVDR and SCD, while accounting for beam divergence. Therefore, the designed mini-beam collimator may enable low-cost and versatile pre-clinical research on mini-beamirradiation.

Feasibility study of a minibeam collimator design for a 60Co gamma irradiator

Recently much attention has been paid to microbeam and minibeam irradiations, present interest focusing on their use in study of the behaviour of single cells, groups of cells, also their application in spatially fractionated radiotherapy. Synchrotrons are the most common source for microbeam radiotherapy (MRT), albeit limited in access and typically offering photon energies very much lower than familiar in the practice of conventional radiotherapy. In this study of feasibility, the design has been investigated of a collimator coupled to a conventional 60Co gamma-irradiator sample chamber to produce a minibeam. MCNPX code Monte Carlo simulations were used to model a Gammacell 220 60Co irradiator with lead and tungsten collimators. The dose profile was evaluated in the absence and presence of the collimator, seeking to optimize collimator design. The results pertain to specific shapes of lead and tungsten collimators producing narrow (millimeter dimension) beams, sufficient in thickness but yet still fitting within the sample chamber, with a peak-to-valley dose ratio (PVDR) greater than 15. The beam size can be tailored with modification in the size of the perforated part, the collimator optimized to minimize the dose-rate at points away from the collimator centre. However the dose-rate at the centre is reduced to between 2 to 20% of that in the absence of collimator. The findings of this study encourage the development of minibeam collimator for gamma irradiators, useful for preclinical minibeam radiotherapy research in centres with little or no access to other appropriate sources.

Biological and dosimetric characterisation of spatially fractionated proton minibeams

The biological effectiveness of proton beams varies with depth, spot size and lateral distance from the beam central axis. The aim of this work is to incorporate proton relative biological effectiveness (RBE) and equivalent uniform dose (EUD) considerations into comparisons of broad beam and highly modulated proton minibeams. A Monte Carlo model of a small animal proton beamline is presented. Dose and variable RBE is calculated on a per-voxel basis for a range of energies (30–109 MeV). For an open beam, the RBE values at the beam entrance ranged from 1.02–1.04, at the Bragg peak (BP) from 1.3 to 1.6, and at the distal end of the BP from 1.4 to 2.0. For a 50 MeV proton beam, a minibeam collimator designed to produce uniform dose at the depth of the BP peak, had minimal impact on the open beam RBE values at depth. RBE changes were observed near the surface when the collimator was placed flush with the irradiated object, due to a higher neutron contribution derived from proton interactions with the collimator. For proton minibeams, the relative mean RBE weighted entrance dose (RWD) was ~25% lower than the physical mean dose. A strong dependency of the EUD with fraction size was observed. For 20 Gy fractions, the EUD varied widely depending on the radiosensitivity of the cells. For radiosensitive cells, the difference was up to ~50% in mean dose and ~40% in mean RWD and the EUD trended towards the valley dose rather than the mean dose. For comparative studies of uniform dose with spatially fractionated proton minibeams, EUD derived from a per-voxel RWD distribution is recommended for biological assessments of reproductive cell survival and related endpoints.

Minibeam radiotherapy with small animal irradiators; in vitro and in vivo feasibility studies

Minibeam radiation therapy (MBRT) delivers an ultrahigh dose of x-ray (⩾100 Gy) in 200–1000 µm beams (peaks), separated by wider non-irradiated regions (valleys) usually as a single temporal fraction. Preclinical studies performed at synchrotron facilities revealed that MBRT is able to ablate tumors while maintaining normal tissue integrity. The main purpose of the present study was to develop an efficient and accessible method to perform MBRT using a conventional x-ray irradiator. We then tested this new method both in vitro and in vivo. Using commercially available lead ribbon and polyethylene sheets, we constructed a collimator that converted the cone beam of an industrial irradiator to 44 identical beams (collimator size ≈ 4 × 10 cm). The dosimetry characteristics of the generated beams were evaluated using two different radiochromic films (beam FWHM = 246 ± 32 µm; center-to-center = 926 ± 23 µm; peak-to-valley dose ratio = 24.35 ± 2.10; collimator relative output factor = 0.84 ± 0.04). Clonogenic assays demonstrated the ability of our method to induce radiobiological cell death in two radioresistant murine tumor cell lines (TRP = glioblastoma; B16-F10 = melanoma). A radiobiological equivalent dose (RBE) was calculated by evaluating the acute skin response to graded doses of MBRT and conventional radiotherapy (CRT). Normal mouse skin demonstrated resistance to doses up to 150 Gy on peak. MBRT significantly extended the survival of mice with flank melanoma tumors compared to CRT when RBE were applied (overall p < 0.001). Loss of spatial resolution deep in the tissue has been a major concern. The beams generated using our collimator maintained their resolution in vivo (mouse brain tissue) and up to 10 cm deep in the radiochromic film. In conclusion, the initial dosimetric, in vitro and in vivo evaluations confirmed the utility of this affordable and easy-to-replicate minibeam collimator for future preclinical studies.

Carbon and oxygen minibeam radiation therapy: An experimental dosimetric evaluation.

To perform dosimetric characterization of a minibeam collimator in both carbon and oxygen ion beams to guide optimal setup geometry and irradiation for future radiobiological studies. Carbon and oxygen minibeams were generated using a prototype tungsten multislit collimator presenting line apertures 700μm wide, which are spaced 3500μm centre-to-centre distance apart. Several radiation beam spots generated the desired field size of 15×15mm2 and production of a 50mm long spread out Bragg peak (SOBP) centered at 80mm depth in water. Dose evaluations were performed with two different detectors: a PTW microDiamond® single crystal diamond detector and radiochromic films (EBT3). Peak-to-valley dose ratio (PVDR) values, output factors (OF), penumbras, and full width at half maximum (FWHM) were measured. Measured lateral dose profiles exhibited spatial fractionation of dose at depth in a water phantom in the expected form of peaks and valleys for both carbon and oxygen radiation fields. The diamond detector and radiochromic film provided measurements of PVDR in good agreement. PVDR values at shallow depth were about 60 and decreased to about 10 at 80mm depth in water. OF in the center of the SOBP was about 0.4; this value is larger than the corresponding one in proton minibeam radiation therapy measured using a comparable collimator due to a reduced lateral scattering for carbon and oxygen minibeams. Carbon and oxygen minibeams may be produced by a mechanical collimator. PVDR values and output factors measured in this first study of these minibeam radiation types indicate there is potential for their therapeutic use. Optimization of minibeam collimator design and the number and size of focal spots for irradiation are advocated to improve PDVR values and dose distributions for each specific applied use.

Dosimetric characterization of an accessory mounted mini-beam collimator across clinically beam matched medical linear accelerators

Background and Purpose. The goal of this project was the dosimetric characterization of a mini-beam collimator across three clinically beam matched medical linear accelerators (linacs). Methods and Materials. The beam quality (%DD(10)), peak-to-valley dose ratio (PVDR), collimator factor and relative output were obtained for 6 MV mini-beam collimated fields of various sizes on three clinically beam matched Varian iX medical linear accelerators. Monte Carlo simulations of the mini-beam collimated fields were used to correlate the experimental results to the accelerators’ electron beam full width-half maximum (FWHM) incident on the Bremsstrahlung target. Results. The beam quality of the mini-beam collimated field on all three linear accelerators agreed with that of the open field beam to within ±1%. PVDR on the different linacs varied by up to ±8.1% from the mean. Similarly, the collimator factors varied from the mean by up to ±3.6%. However, changes in the mini-beam collimated field due to changes in collimator inclination with respect to the beam central axis or field size were consistent across the three linacs. The collimator factors of the linacs were found to decrease by up to 7.1% in response to changes in inclination of less than 0.1°, and have an inverse relationship to field size. Monte Carlo simulations indicated that the disagreement in collimator factor can be linked to variation in the spatial width of the electron beam incident on the Bremsstrahlung target. Conclusion. A mini-beam collimator has been dosimetrically characterized on three clinically beam matched medical linear accelerators. Discrepancies in the mini-beam collimated field characteristics were observed across accelerators. Monte Carlo simulation revealed that these differences were related to the linac electron beam FWHM.

Optimization of minibeam generation by mechanical collimation in proton minibeam radiation therapy

Introduction The dose tolerances of normal tissues continue being the main barrier in radiotherapy. To lower it, we recently proposed a novel concept: proton minibeam radiation therapy (pMBRT). It allies the inherent advantages of protons with the normal tissue preservation observed when irradiated with submillimetric spatially fractionated beams. The tumor receives a homogeneous dose distribution, while normal tissues benefit from the spatial fractionation of the dose. Purpose We have recently implemented this technique at the Orsay proton therapy clinical center. This work aims at optimizing the minibeam generation by means of a mechanical collimation. Materials and methods Monte Carlo simulations (GATEv7.1) were used to evaluate different irradiation configurations, e.g. collimator dimensions and materials (Brass, Tungsten, Iron and Nickel). Clinically relevant energies were used. Neutron contamination, Peak-to-valley dose ratios (PVDR) and beam penumbras were used as figures-of-merit. Results The neutron dose due to the minibeam collimator was found to be lower than 0.002% of the primary dose. A tungsten collimator provides the higher PVDR, but the generated neutron yield is 3 times higher than in other materials. Brass seems to provide the best compromise between PVDR values and neutron contamination. Conclusion A mechanical collimation only increases the biologic neutron dose by 0.04% of the peak surface dose therefore it is suitable for pMBRT. An optimized collimation for pMBRT, providing the best compromise between a high PVDR and low neutron generation, has been obtained.

Parts per Million Powder X-ray Diffraction

Here we demonstrate the use of second harmonic generation (SHG) microscopy-guided synchrotron powder X-ray diffraction (PXRD) for the detection of trace crystalline active pharmaceutical ingredients in a common polymer blend. The combined instrument is capable of detecting 100 ppm crystalline ritonavir in an amorphous hydroxypropyl methylcellulose matrix with a high signal-to-noise ratio (>5000). The high spatial resolution afforded by SHG microscopy allows for the use of a minibeam collimator to reduce the total volume of material probed by synchrotron PXRD. The reduction in probed volume results in reduced background from amorphous material. The ability to detect low crystalline loading has the potential to improve measurements in the formulation pipeline for pharmaceutical solid dispersions, for which even trace quantities of crystalline active ingredients can negatively impact the stability and bioavailability of the final drug product.

Medical linear accelerator mounted mini-beam collimator: design, fabrication and dosimetric characterization

The goal of this work was to design, build and experimentally characterize a linear accelerator mounted mini-beam collimator for use at a nominal 6 MV beam energy. Monte Carlo simulation was used in the design and dosimetric characterization of a compact mini-beam collimator assembly mounted to a medical linear accelerator. After fabrication, experimental mini-beam dose profiles and central axis relative output were measured and the results used to validate the simulation data. The simulation data was then used to establish traceability back to an established dosimetric code of practice. The Monte Carlo simulation work revealed that changes in collimator blade width have a greater influence on the valley-to-peak dose ratio than do changes in blade height. There was good agreement between the modeled and measured profile data, with the exception of small differences on either side of the central peak dose. These differences were found to be systematic across all depths and result from limitations associated with the collimator fabrication. Experimental mini-beam relative output and simulation data agreed to better than ±2.0%, which is well within the level of uncertainty required for dosimetric traceability of non-standard field geometries. A mini-beam collimator has now been designed, built and experimentally characterized for use with a commercial linear accelerator operated at a nominal 6 MV beam energy.

Automated High-Throughput Data Collection at IMCA-CAT

The Industrial Macromolecular Crystallography Association Collaborative Access Team (IMCA-CAT) operates a data collection facility at the Advanced Photon Source for protein crystallography. IMCA-CAT meets the demands of IMCA member pharmaceutical companies for reliable, high-quality, high-throughput data collection, while ensuring a secure environment for proprietary research. The 17ID micro-focused high-flux insertion device beamline, equipped with a Pilatus 6M pixel array detector, allows for very fast data collection times. The focused beam size (30 μm x 70 μm) can be easily optimized for each sample using a GM/CA-CAT mini-beam quad collimator, with user-selectable beam sizes of 50, 20, 10 and 5 μm. An Alio goniometer has a small (1.2 μm) sphere of confusion, providing stable sample positioning, and X-ray beam position is maintained within 2 μm by custom software in real time. Automated sample mounting is performed with a Rigaku ACTOR robot, accepting both Rigaku and ALS/Unipuck style magazines, providing fast yet reliable sample exchanges and enabling remote access and unattended data collection. Rigaku JDirector software for robot control and data collection has been customized to incorporate additional tools, such as diffraction-based sample centering for both manual and unattended data collection modes, vector data collection and inverse beam anomalous data collection. While targeting the needs of industrial research, the automation and rapid data collection times at 17ID are also ideally suited for structural genomics and other research efforts requiring high-throughput experiments. Access is available to interested researchers through the APS General User Program and through subscription memberships for those needing regular and guaranteed proprietary beamtime.

Collimator design for experimental minibeam radiation therapy

To design and optimize a minibeam collimator for minibeam radiation therapy studies using a 250 kVp x-ray machine as a simulated synchrotron source. A Philips RT250 orthovoltage x-ray machine was modeled using the EGSnrc/BEAMnrc Monte Carlo software. The resulting machine model was coupled to a model of a minibeam collimator with a beam aperture of 1 mm. Interaperture spacing and collimator thickness were varied to produce a minibeam with the desired peak-to-valley ratio. Proper design of a minibeam collimator with Monte Carlo methods requires detailed knowledge of the x-ray source setup. For a cathode-ray tube source, the beam spot size, target angle, and source shielding all determine the final valley-to-peak dose ratio. A minibeam collimator setup was created, which can deliver a 30 Gy peak dose minibeam radiation therapy treatment at depths less than 1 cm with a valley-to-peak dose ratio on the order of 23%.

Mini-beam collimator applications at the Advanced Photon Source

Abstract In 2007, the General Medicine and Cancer Institutes Collaborative Access Team (GM/CA CAT, Sector 23, Advanced Photon Source) began providing mini-beam collimators to its users. These collimators contained individual, 5- or 10-μm pinholes and were rapidly exchangeable, thereby allowing users to tailor the beam size to their experimental needs. The use of these collimators provided a reduction in background noise, and thus improved the signal-to-noise ratio [1] , [2] . Recent improvements in the collimator design include construction of the device from a monolithic piece of molybdenum with multiple pinholes mounted inside [3] . This allows users to select from various size options from within the beamline control software without the realignment that was previously necessary. In addition, a new, 20-μm pinhole has been added to create a “quad-collimator”, resulting in greater flexibility for the users. The mini-beam collimator is now available at multiple crystallographic beamlines and also is a part of the first Mossbauer Microscopic system at sector 3-ID.