Australian Synchrotron Research Articles

Abstract ID: 198 Monte Carlo simulation and simple model of dose distribution in synchrotron radiation rotational radiotherapy of breast cancer: An experimental phantom study

External beam rotational radiotherapy of breast cancer with kilovoltage photons (kV-EBRT), with the patient in prone position, has been proposed [1] as a possible alternative to conventional radiotherapy with two tangential 6-MV X-ray beams produced by a medical linac with a supine patient. kV-EBRT uses a dedicated setup initially developed for breast CT, with a 320-kVp beam from an orthovoltage X-ray tube rotating in full circles around the breast; CT for tumour localization can be performed by using the same setup. Though dose build-up is not present, rotational summation of dose delivery allows a skin sparing comparable to conventional radiotherapy. We proposed the use of a monoenergetic synchrotron radiation (SR) collimated beam for image-guided rotational radiotherapy for the pendant breast (SR3T) [2] . The high flux of SR permits dose rates even greater to that of conventional radiotherapy, while the optimal photon energy can be selected for the treatment. In this work, we present Monte Carlo simulation and a simple model for evaluation of the 3D dose distribution in SR3T. The MC code was based on GEANT4 toolkit ver.10.00. We validated these simulations via measurements on breast phantoms performed at the Imaging and Medical Beamline of the Australian Synchrotron. We measured the dose distribution in cylindrical PMMA and polyethylene phantoms at 60 keV, using an ionization chamber, thermoluminescent dosimeters and radiochromic films. This study indicated that for a tumour localized at the centre of a mid-sized breast (14-cm diameter at chest wall), a ”skin-to-tumour” dose ratio of 14% can be reached at 60 keV with a collimated SR beam. Non uniform dose distribution to the target (dose painting) can be performed with multiple rotations around the organ. Kilovoltage SR3T with suitable radiosensitizers may exploit the dose enhancement factor due to increased photoelectric absorption, at SR beam energies in the 60–110 keV range.

Abstract ID: 21 Simulation of synchrotron-based microbeam radiation therapy using Geant4

Microbeam Radiation Therapy (MRT) is a preclinical radiotherapy modality characterised by the use of many micron-sized, spatially fractionated, high intensity radiation fields produced by a Multi-Slit Collimator and synchrotron light [1] . A typical MRT radiation field consists of multiple high dose ‘peaks’ separated by low dose ‘valleys’ (width 25–50 μm; pitch 100–400 μm) delivered with dose rates of up to 10 kGy/s. The minute field size and high dose rate of MRT requires good Quality Assurance in order to transition into the clinical field. Dose Verification and Treatment Planning Systems (TPS) are crucial aspects of quality assurance, allowing for independent prediction and verification of dose distributions delivered to patients. The most accurate form of TPS is Monte Carlo computer simulations. The Centre for Medical Radiation Physics (CMRP), University of Wollongong, has developed a Geant4-based synchrotron beamline model for dose verification at the Australian Synchrotron Imaging and Medical Beamline (IMBL). This model, denoted G4IMBL, uses a multi-stage procedure to generate synchrotron light, transport through the beamline model, and calculate dose deposition in a phantom. G4IMBL models the production of X-ray photons entirely using Geant4 by transporting electrons through the sinusoidal magnetic field of a wiggler. This allows for optimisation of multiple operation modes via tuning of wiggler magnetic field strength and electron steering angle. The simulation has been validated against experimental measurements and is used to characterise novel Quality Assurance silicon based detectors with sub-mm spatial resolution, developed at CMRP. The development, optimisation, and validation of this Geant4-based software tool for MRT Quality Assurance will be presented.

X-ray microbeam measurements with a high resolution scintillator fibre-optic dosimeter

Synchrotron microbeam radiation therapy is a novel external beam therapy under investigation, that uses highly brilliant synchrotron x-rays in microbeams 50 μm width, with separation of 400 μm, as implemented here. Due to the fine spatial fractionation dosimetry of these beams is a challenging and complicated problem. In this proof-of-concept work, we present a fibre optic dosimeter that uses plastic scintillator as the radiation conversion material. We claim an ideal one-dimensional resolution of 50 μm. Using plastic scintillator and fibre optic makes this dosimeter water-equivalent, a very desirable dosimetric property. The dosimeter was tested at the Australian Synchrotron, on the Imaging and Medical Beam-Line. The individual microbeams were able to be resolved and the peak-to-valley dose ratio and the full width at half maximum of the microbeams was measured. These results are compared to a semiconductor strip detector of the same spatial resolution. A percent depth dose was measured and compared to data acquired by an ionisation chamber. The results presented demonstrate significant steps towards the development of an optical dosimeter with the potential to be applied in quality assurance of microbeam radiation therapy, which is vital if clinical trials are to be performed on human patients.

Micro-computed tomographic analysis of the radial geometry of intrarenal artery-vein pairs in rats and rabbits: Comparison with light microscopy.

We assessed the utility of synchrotron-radiation micro-computed tomography (micro-CT) for quantification of the radial geometry of the renal cortical vasculature. The kidneys of nine rats and six rabbits were perfusion fixed and the renal circulation filled with Microfil. In order to assess shrinkage of Microfil, rat kidneys were imaged at the Australian Synchrotron immediately upon tissue preparation and then post fixed in paraformaldehyde and reimaged 24hours later. The Microfil shrank only 2-5% over the 24hour period. All subsequent micro-CT imaging was completed within 24hours of sample preparation. After micro-CT imaging, the kidneys were processed for histological analysis. In both rat and rabbit kidneys, vascular structures identified in histological sections could be identified in two-dimensional (2D) micro-CT images from the original kidney. Vascular morphology was similar in the two sets of images. Radial geometry quantified by manual analysis of 2D images from micro-CT was consistent with corresponding data generated by light microscopy. However, due to limited spatial resolution when imaging a whole organ using contrast-enhanced micro-CT, only arteries ≥100 and ≥60μm in diameter, for the rat and rabbit respectively, could be assessed. We conclude that it is feasible and valid to use micro-CT to quantify vascular geometry of the renal cortical circulation in both the rat and rabbit. However, a combination of light microscopic and micro-CT approaches are required to evaluate the spatial relationships between intrarenal arteries and veins over an extensive range of vessel size.

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered 'random'. This would then allow the supposedly incoherent contribution from the electronic motion to be treated as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. This paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene.

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered 'random'. This would then allow the supposedly incoherent contribution from the electronic motion to be treated as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. This paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.

Estimating the absolute flux distribution for a synchrotron X-ray beam using ionization-chamber measurements with various filters.

It is shown that an extensive set of accurate ionization-chamber measurements with a primary polychromatic synchrotron X-ray beam transmitted through various filter combinations/thicknesses can be used to quite effectively estimate the absolute flux distribution. The basic technique is simple but the `inversion' of the raw data to extract the flux distribution is a fundamentally ill-posed problem. It is demonstrated, using data collected at the Imaging and Medical Beamline (IMBL) of the Australian Synchrotron, that the absolute flux can be quickly and reliably estimated if a suitable choice of filters is made. Results are presented as a function of the magnetic field (from 1.40 to 4.00 T) of the superconducting multi-pole wiggler insertion device installed at IMBL. A non-linear least-squares refinement of the data is used to estimate the incident flux distribution and then comparison is made with calculations from the programs SPECTRA, XOP and spec.exe. The technique described is important not only in estimating flux itself but also for a variety of other, derived, X-ray properties such as beam quality, power density and absorbed-dose rate. The applicability of the technique with a monochromatic X-ray beam for which there is significant harmonic contamination is also demonstrated. Whilst absolute results can also be derived in this monochromatic beam case, relative (integrated) flux values are sufficient for our primary aim of establishing reliable determinations of the percentages of the various harmonic components.

Characterization of heat treatment-induced pore structure changes in cold-sprayed titanium

Two X-ray computed tomography (CT) datasets have been acquired for a cold-sprayed titanium sample before and after heat treatment. The datasets were collected with a beam energy of 30keV at the Australian Synchrotron. Three-dimensional (3D) distributions of porosity in the Ti sample were reconstructed using a data-constrained modelling (DCM) technique. Quantitative analysis indicated that the heat treatment caused morphological changes to the pores and a small decrease in the overall porosity. After heat treatment, some fine porosity disappeared while the large porosity regions were essentially unaffected except for a change towards a more rounded pore shape. Interconnectivity between pores was reduced, which has implications for sealing and trapping of contaminant gases in cold-sprayed parts. The characterization technique and the workflow presented in the paper are applicable to non-destructive 3D characterization of other materials.

Smoking gun for thallium geochemistry in volcanic arcs: Nataliyamalikite, TlI, a new thallium mineral from an active fumarole at Avacha Volcano, Kamchatka Peninsula, Russia

This paper describes the new mineral nataliyamalikite, the orthorhombic form of thallium iodide (TlI), from high-temperature fumaroles from the Avacha volcano, Kamchatka Peninsula, Russia. We also present some chemical analyses showing extreme enrichment of Tl in the volcanic gases at the Avacha volcano, and a review of thallium geochemistry that highlights the fascinating processes that led to the formation of nataliyamalikite. Nataliyamalikite occurs as pseudo-cubic nanocrystals (≤0.5 μm) within vacuoles in an As-(Te)-rich amorphous sulfur matrix and rarely as irregularly shaped aggregates up to ~50 μm in diameter within the amorphous sulfur matrix. Associated minerals include an unidentified Tl-As-S mineral, barite, and rare inclusions of a Re-Cu-bearing phase. The mean empirical composition based on four EDS analyses is Tl 1.00 (I 0.95 Br 0.03 Cl 0.02 ), corresponding to the ideal formula TlI. Nataliyamalikite crystallizes in the orthorhombic system, space group Cmcm , which is consistent with the low-temperature ( Pm 3 m ) of the high-temperature polymorph, although most analyzed grains display the orthorhombic symmetry. Single-crystal X-ray studies of material extracted by the focused ion beam-scanning electron microscopy (FIB-SEM) technique, and carried out on the MX2 macromolecular beamline of the Australian Synchrotron, determined the following cell dimensions: a = 4.5670(9), b = 12.803(3), c = 5.202(1) A, V = 304.2(1) A 3 , and Z = 4. The six strongest calculated X-ray reflections and their relative intensities are: 3.31 (100), 2.674 (73), 3.20 (43), 2.601 (28), 2.019 (21), and 2.284 A (19). The combination of EBSD analysis (providing an efficient test of the crystallinity and crystal symmetry of a population of micrometer-sized grains) and synchrotron single-crystal X-ray micro-diffraction (beam size ~7.5 μm) on micro-aggregates extracted using FIB-SEM opens the way to the characterization of challenging specimen—in this case, the sulfur matrix is highly beam sensitive, and the nataliyamalikite grains could not be isolated using optical microscopy. The high-temperature (>600 °C) sulfidic (~1.2 wt% S) vapors at Avacha are extremely enriched in thallium; with 34 ppm, they contain an order of magnitude more Tl than the richest volcanic gases analyzed to date and ~100× more Tl than most metal-rich fumarolitic fluids associated with volcanic arcs. The formation of nataliyamalikite illustrates the complex processes that control thallium geochemistry in magmatic arc systems. Thallium minerals have now been reported in andesitic (Avacha), basaltic (Tolbachik, Kamchatka), as well as rhyolitic (Vulcano, Eolian Islands, Italy) volcanoes. Ultimately, these thallium minerals result from the transfer of thallium from subducted sediments to volcanic gases in arc volcanoes. We suggest that the extremely thallium-enriched vapors from which nataliyamalikite formed result from complex and transient interactions between Tl-rich sulfosalt melts and magmatic vapors, a process that may be important in controlling metal distribution in boiling epithermal systems.

Towards breast cancer rotational radiotherapy with synchrotron radiation

PurposeWe performed the first investigations, via measurements and Monte Carlo simulations on phantoms, of the feasibility of a new technique for synchrotron radiation rotational radiotherapy for breast cancer (SR3T). MethodsA Monte Carlo (MC) code based on Geant4 toolkit was developed in order to simulate the irradiation with the SR3T technique and to evaluate the skin sparing effect in terms of centre-to-periphery dose ratio at different energies in the range 60–175keV. Preliminary measurements were performed at the Australian Synchrotron facility. Radial dose profiles in a 14-cm diameter polyethylene phantom were measured with a 100-mm pencil ionization chamber for different beam sizes and compared with the results of MC simulations. Finally, the dose painting feasibility was demonstrated with measurements with EBT3 radiochromic films in a phantom and collimating the SR beam at 1.5cm in the horizontal direction. ResultsMC simulations showed that the SR3T technique assures a tumour-to-skin absorbed dose ratio from about 7:1 (at 60keV photon energy) to about 10:1 (at 175keV), sufficient for skin sparing during radiotherapy. The comparison between the results of MC simulations and measurements showed an agreement within 5%. Two off-centre foci were irradiated shifting the rotation centre in the horizontal direction. ConclusionsThe SR3T technique permits to obtain different dose distributions in the target with multiple rotations and can be guided via synchrotron radiation breast computed tomography imaging, in propagation based phase-contrast conditions. Use of contrast agents like iodinated solutions or gold nanoparticles for dose enhancement (DE-SR3T) is foreseen and will be investigated in future work.

Preclinical radiotherapy at the Australian Synchrotron's Imaging and Medical Beamline: instrumentation, dosimetry and a small-animal feasibility study.

Therapeutic applications of synchrotron X-rays such as microbeam (MRT) and minibeam (MBRT) radiation therapy promise significant advantages over conventional clinical techniques for some diseases if successfully transferred to clinical practice. Preclinical studies show clear evidence that a number of normal tissues in animal models display a tolerance to much higher doses from MRT compared with conventional radiotherapy. However, a wide spread in the parameters studied makes it difficult to make any conclusions about the associated tumour control or normal tissue complication probabilities. To facilitate more systematic and reproducible preclinical synchrotron radiotherapy studies, a dedicated preclinical station including small-animal irradiation stage was designed and installed at the Imaging and Medical Beamline (IMBL) at the Australian Synchrotron. The stage was characterized in terms of the accuracy and reliability of the vertical scanning speed, as this is the key variable in dose delivery. The measured speed was found to be within 1% of the nominal speed for the range of speeds measured by an interferometer. Furthermore, dose measurements confirm the expected relationship between speed and dose and show that the measured dose is independent of the scan direction. Important dosimetric parameters such as peak dose, valley dose, the collimator output factor and peak-to-valley dose ratio are presented for 5 mm × 5 mm, 10 mm × 10 mm and 20 mm × 20 mm field sizes. Finally, a feasibility study on three glioma-bearing rats was performed. MRT and MBRT doses were prescribed to achieve an average dose of 65 Gy in the target, and magnetic resonance imaging follow-up was performed at various time points after irradiation to follow the tumour volume. Although it is impossible to draw conclusions on the different treatments with such a small number of animals, the feasibility of end-to-end preclinical synchrotron radiotherapy studies using the IMBL preclinical stage is demonstrated.

High-resolution mucociliary transport measurement in live excised large animal trachea using synchrotron X-ray imaging

BackgroundThe Australian Synchrotron Imaging and Medical Beamline (IMBL) was designed as the world’s widest synchrotron X-ray beam, enabling both clinical imaging and therapeutic applications for humans as well as the imaging of large animal models. Our group is developing methods for imaging the airways of newly developed CF animal models that display human-like lung disease, such as the CF pig, and we expect that the IMBL can be utilised to image airways in animals of this size.MethodsThis study utilised samples of excised tracheal tissue to assess the feasibility, logistics and protocols required for airway imaging in large animal models such as pigs and sheep at the IMBL. We designed an image processing algorithm to automatically track and quantify the tracheal mucociliary transport (MCT) behaviour of 103 μm diameter high refractive index (HRI) glass bead marker particles deposited onto the surface of freshly-excised normal sheep and pig tracheae, and assessed the effects of airway rehydrating aerosols.ResultsWe successfully accessed and used scavenged tracheal tissue, identified the minimum bead size that is visible using our chosen imaging setup, verified that MCT could be visualised, and that our automated tracking algorithm could quantify particle motion. The imaging sequences show particles propelled by cilia, against gravity, up the airway surface, within a well-defined range of clearance speeds and with examples of ‘clumping’ behaviour that is consistent with the in vivo capture and mucus-driven transport of particles.ConclusionThis study demonstrated that the wide beam at the IMBL is suitable for imaging MCT in ex vivo tissue samples. We are now transitioning to in vivo imaging of MCT in live pigs, utilising higher X-ray energies and shorter exposures to minimise motion blur.

Synchrotron microbeam radiotherapy in a commercially available treatment planning system

In this paper we use a research licensed version of the EclipseTM treatment planning system (TPS) from Varian Medical Systems, Inc. to develop a novel treatment planning environment for synchrotron microbeam radiotherapy (MRT). This research license allows for customised dose calculation algorithms to be integrated with the clinical work-flows in Eclipse that are typical to modern radiotherapy. In this way, all the functionality of the Eclipse TPS familiar to many radiation oncology professionals is retained for application to MRT. Our TPS is designed for the dynamic MRT modality that has been developed for the imaging and medical beamline (IMBL) at the Australian synchrotron. The TPS uses a very simple algorithm for primary dose calculation, and we estimate the peak to valley dose ratio (PVDR) and hence the valley dose from data derived from a separate Monte Carlo simulation. At this stage the algorithm is a fast approximation with only simple radiological path length corrections to account for tissue inhomogeneities. However, the algorithm can highlight to oncology clinicians the strengths and limitations of synchrotron MRT, and furthermore, serves as a proof of concept and a start-point for implementing more advanced dose calculation algorithms. For the treatment itself, the incident synchrotron broad beam is collimated to a 30 mm wide by 1 mm high field which illuminates the MRT collimator, which in turn produces 50 μm wide vertical microbeams separated at 400 μm centre-to-centre. The sample and a mask is then dynamically swept through this array of microbeams, producing a dose of radiation in the sample that is conformal to a patient specific mask aperture. All properties of this irradiation methodology can be configured within the TPS and used for the design of MRT treatments. We present implementation details of our TPS for MRT and describe the hyperbolic relationship between PVDR and depth, and use it for calculating the water equivalent PVDR at different radiological depths.

X-Tream dosimetry of highly brilliant X-ray microbeams in the MRT hutch of the Australian Synchrotron

The X-Tream dosimetry system developed at the Centre for Medical Radiation Physics (University of Wollongong, Australia) utilises a high resolution silicon Single Strip Detector to characterise synchrotron radiation microbeams for the purpose of Quality Assurance of Microbeam Radiation Therapy. Firstly, a comparison of the Silicon Strip Detector performance with respect to a conventional PinPoint Ionisation Chamber for broad beams and microbeams is given. These results are then extended to characterise the horizontal microbeam radiation field available in the high flux experimental hutch of the Imaging and Medical BeamLine at the Australian Synchrotron. The Silicon Strip Detector measured depth dose curve of the broad beam agrees very well with the PinPoint Ionisation Chamber measurements between 10 and 50 mm depth in water. Significant deviations from the PinPoint Ionisation Chamber response are observed with increasing depth. Microbeam profiles measured by the Silicon Strip Detector are well resolved but clearly affected by misalignment of the Silicon Strip Detector with respect to the microbeams. Future beamline technical improvements will alleviate this issue.

Methods and methodology for FTIR spectral correction of channel spectra and uncertainty, applied to ferrocene

We present methodology for the first FTIR measurements of ferrocene using dilute wax solutions for dispersion and to preserve non-crystallinity; a new method for removal of channel spectra interference for high quality data; and a consistent approach for the robust estimation of a defined uncertainty for advanced structural χr2 analysis and mathematical hypothesis testing. While some of these issues have been investigated previously, the combination of novel approaches gives markedly improved results. Methods for addressing these in the presence of a modest signal and how to quantify the quality of the data irrespective of preprocessing for subsequent hypothesis testing are applied to the FTIR spectra of Ferrocene (Fc) and deuterated ferrocene (dFc, Fc-d10) collected at the THz/Far-IR beam-line of the Australian Synchrotron at operating temperatures of 7K through 353K.

Quantitative characterization of the X-ray beam at the Australian Synchrotron Imaging and Medical Beamline (IMBL).

A critical early phase for any synchrotron beamline involves detailed testing, characterization and commissioning; this is especially true of a beamline as ambitious and complex as the Imaging & Medical Beamline (IMBL) at the Australian Synchrotron. IMBL staff and expert users have been performing precise experiments aimed at quantitative characterization of the primary polychromatic and monochromatic X-ray beams, with particular emphasis placed on the wiggler insertion devices (IDs), the primary-slit system and any invacuo and ex vacuo filters. The findings from these studies will be described herein. These results will benefit IMBL and other users in the future, especially those for whom detailed knowledge of the X-ray beam spectrum (or `quality') and flux density is important. This information is critical for radiotherapy and radiobiology users, who ultimately need to know (to better than 5%) what X-ray dose or dose rate is being delivered to their samples. Various correction factors associated with ionization-chamber (IC) dosimetry have been accounted for, e.g.ion recombination, electron-loss effects. A new and innovative approach has been developed in this regard, which can provide confirmation of key parameter values such as the magnetic field in the wiggler and the effective thickness of key filters. IMBL commenced operation in December 2008 with an Advanced Photon Source (APS) wiggler as the (interim) ID. A superconducting multi-pole wiggler was installed and operational in January 2013. Results are obtained for both of these IDs and useful comparisons are made. A comprehensive model of the IMBL has been developed, embodied in a new computer program named spec.exe, which has been validated against a variety of experimental measurements. Having demonstrated the reliability and robustness of the model, it is then possible to use it in a practical and predictive manner. It is hoped that spec.exe will prove to be a useful resource for synchrotron science in general, and for hard X-ray beamlines, whether they are based on bending magnets or insertion devices, in particular. In due course, it is planned to make spec.exe freely available to other synchrotron scientists.

Synchrotron activation radiotherapy: Effects of dose-rate and energy spectra to tantalum oxide nanoparticles selective tumour cell radiosentization enhancement

Synchrotron radiation is unique in its ability to deliver dose at high dose rates using kiloelectronvolt photons. We are investigating the use of Tantalum pentoxide (Ta2O5) nano-structured particles (NSPs) that are to date unexplored in synchrotron radiation fields as they have high atomic number (Z=73) are biocompatible and are therefore potential radio sensitizers. We exposed cell culture flasks containing 9L gliosarcoma tumour cells or Madin-Darby Canine Kidney (MDCK) non-tumour cells to the NSPs and treated the cells using a broad synchrotron beam (140 keV median energy; average dose rate of 50 Gy/s) at the Australian Synchrotron. We compare the results with those from similar cells treated using a conventional 150 kVp orthovoltage field (dose rate of 0.0127 Gy/s). The results reveal that the high dose-rate synchrotron irradiation is more effective at killing the 9L cells relative to the MDCK cells than the orthovoltage irradiation. On the other hand, the NSPs are more effective at radiosensitizing the 9L cells compared to the MDCK cells in the orthovoltage radiation field, which is due to the NSP energy dependence in the kilovoltage energy range. Both the dose rate and energy spectrum need to be considered in future studies with synchrotron activation radiotherapy (SART).

X-ray crystal structure of a malonate-semialdehyde dehydrogenase from Pseudomonas sp. strain AAC.

The NAD-dependent malonate-semialdehyde dehydrogenase KES23460 from Pseudomonas sp. strain AAC makes up half of a bicistronic operon responsible for β-alanine catabolism to produce acetyl-CoA. The KES23460 protein has been heterologously expressed, purified and used to generate crystals suitable for X-ray diffraction studies. The crystals belonged to space group P212121 and diffracted X-rays to beyond 3 Å resolution using the microfocus beamline of the Australian Synchrotron. The structure was solved using molecular replacement, with a monomer from PDB entry 4zz7 as the search model.

New 3D Silicon detectors for dosimetry in Microbeam Radiation Therapy

Microbeam Radiation Therapy (MRT) involves the use of a spatially fractionated beam of synchrotron generated X-rays to treat tumours. MRT treatment is delivered via an array of high dose ‘peaks’ separated by low dose ‘valleys’. A good Peak to Valley Dose Ratio (PVDR) is an important indicator of successful treatment outcomes. MRT dosimetry requires a radiation hard detector with high spatial resolution, large dynamic range, which is ideally real-time and tissue equivalent. We have developed a Silicon Strip Detector (SSD) and very recently, a new 3D MESA SSD to meet the very stringent requirements of MRT dosimetry. We have compared these detectors through the characterisation of the MRT radiation field at the Australian Synchrotron Imaging and Medical Beamline. The EPI SSD was able to measure the microbeam profiles and PVDRs, however the effective spatial resolution was limited by the detector alignment options available at the time. The geometry of the new 3D MESA SSD is less sensitive to this alignment restriction was able to measure the microbeam profiles within 2 μm of that expected. The 3D MESA SSD measured PVDRs were possibly affected by undesired and slow charge collection outside the sensitive volume and additional scattering from the device substrate.

Crystal structure of a putrescine aminotransferase from Pseudomonas sp. strain AAC.

The putrescine aminotransferase KES24511 from Pseudomonas sp. strain AAC was previously identified as an industrially relevant enzyme based on the discovery that it is able to promiscuously catalyse the transamination of 12-aminododecanoic acid. Here, the cloning, heterologous expression, purification and successful crystallization of the KES24511 protein are reported, which ultimately generated crystals adopting space group I2. The crystals diffracted X-rays to 2.07 Å resolution and data were collected using the microfocus beamline of the Australian Synchrotron. The structure was solved using molecular replacement, with a monomer from PDB entry 4a6t as the search model.