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This work presents an in-depth analysis into the dependencies of radiosensitisation on X-ray beam energy, particle morphology and particle concentration for Ta2O5 nanostructured particles. A maximum sensitisation enhancement ratio of 1.46 was attained with irradiation of a 10 MV x-ray photon beam on 9L cells exposed to the less aggregated form of NSPs at 500 μg/mL-1. A significant increase in sensitisation of 30% was noted at 150 kVp for irradiation of the less aggregated form of tantalum pentoxide NSPs compared to its more agglomerated counterpart. Interestingly, no differences in sensitisation were observed between 50 and 500 μg/mL-1 for all beam energies and NSPs tested. This is explained by a physical "shell effect", where by the NSPs form layers around the cells (observed using confocal microscopy), with the inner layers contributing to enhancement, while the outer layers shield the cell from damage.

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 ¿m 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.

Laser-accelerated proton beams exhibit remarkably different beam characteristics as compared to conventionally accelerated ion beams. About 105 to 107 particles per MeV and msr are accelerated quasi-instantaneously within about 1 ps. The resulting energy spectrum typically shows an exponentially decaying distribution. Our planned approach to determine the energy spectrum of the particles generated in each pulse is to exploit the time-of-flight (TOF) difference of protons with different kinetic energies at 1 m distance from the laser-target interaction. This requires fast and sensitive detectors. We therefore tested two prototype silicon detectors, developed at the Centre for Medical Radiation Physics at the University of Wollongong with a current amplifier, regarding their suitability for TOF-spectrometry in terms of sensitivity and timing properties. For the latter, we illuminated the detectors with short laser pulses, measured the signal current and compared it to the signal of a fast photodiode. The comparison revealed that the timing properties of both prototypes are not yet sufficient for our purpose. In contrast, our results regarding the detectors' sensitivity are promising. The lowest detectable proton flux at 10 MeV was found to be 25 protons per ns on the detector. With this sensitivity and with a smaller pixelation of the detectors, the timing properties can be improved for new prototypes, making them potential candidates for TOF-spectrometry of laser-accelerated particle beams.

PurposeProton computed tomography (pCT) is a promising imaging technique to substitute or at least complement x-ray CT for more accurate proton therapy treatment planning as it allows calculating directly proton relative stopping power from proton energy loss measurements. A proton CT scanner with a silicon-based particle tracking system and a five-stage scintillating energy detector has been completed. In parallel a modular software platform was developed to characterize the performance of the proposed pCT.MethodThe modular pCT software platform consists of (1) a Geant4-based simulation modeling the Loma Linda proton therapy beam line and the prototype proton CT scanner, (2) water equivalent path length (WEPL) calibration of the scintillating energy detector, and (3) image reconstruction algorithm for the reconstruction of the relative stopping power (RSP) of the scanned object. In this work, each component of the modular pCT software platform is described and validated with respect to experimental data and benchmarked against theoretical predictions. In particular, the RSP reconstruction was validated with both experimental scans, water column measurements, and theoretical calculations.ResultsThe results show that the pCT software platform accurately reproduces the performance of the existing prototype pCT scanner with a RSP agreement between experimental and simulated values to better than 1.5%.ConclusionsThe validated platform is a versatile tool for clinical proton CT performance and application studies in a virtual setting. The platform is flexible and can be modified to simulate not yet existing versions of pCT scanners and higher proton energies than those currently clinically available.

The Bonner Sphere Spectrometer (BSS) system is a well-established technique for neutron dosimetry that involves detection of thermal neutrons within a range of hydrogenous moderators. BSS detectors are often used to perform neutron field surveys in order to determine the ambient dose equivalent H*(10) and estimate health risk to personnel. There is a potential limitation of existing neutron survey techniques, since some detectors do not consider the direction of the neutron field, which can result in overly conservative estimates of dose in neutron fields. This paper shows the development of a Geant4 simulation application to characterise a prototype neutron detector based on three orthogonal 3He tubes inside a single HDPE sphere built at the Australian Nuclear Science and Technology Organisation (ANSTO). The Geant4 simulation has been validated with respect to experimental measurements performed with an Am-Be source.

In this paper we report a Geant4 simulation study to investigate the characteristic prompt gamma (PG) emission in a water phantom for real-time monitoring of the Bragg peak (BP) during proton beam irradiation. The PG production, emission spatial correlation with the BP, and position preference for detection with respect to the BP have been quantified in different PG energy windows as a function of proton pencil-beam energy from 100 to 200. MeV. The PG response to small BP shifts was evaluated using a 2. cm-thick slab with different human body materials embedded in a water phantom. Our results show that the prominent characteristic PG emissions of 4.44, 5.21 and 6.13. MeV exhibit distinctive correlation with the dose deposition curve. The accuracy in BP position identification using these characteristic PG rays is highly consistent as the beam energy increases from 100 to 200. MeV. There exists a position preference for PG detection with respect to the BP position, which has a strong dependence on the proton beam energy and PG energies. It was also observed that a submillimeter shift of the BP position can be realized by using PG signals. These results indicate that the characteristic PG signal is sensitive and reliable for BP tracking. Although the maximization of the PG measurement associated with the BP is difficult, it can be optimized with energy and detection position preferences.

Two Dimensional (2D) silicon diode arrays are often implemented in radiation therapy quality assurance (QA) applications due to their advantages such as: real-time operation (compared to the films), large dynamic range and small size (compared to ionization chambers). The Centre for Medical Radiation Physics, University of Wollongong has developed a multifunctional 2D silicon diode array known as the Magic Plate (MP) for real-time applications and is suitable as a transmission detector for photon flunce mapping (MPTM) or for in phantom dose mapping (MPDM). The paper focusses on the characterisation of the MPDM in terms of output factor and square field beam profiling in 6 MV, 10 MV and 18 MV clinical photon fields. We have found excellent agreement with three different ion chambers for all measured parameters with output factors agreeing within 1.2% and field profiles agreeing within 3% and/or 3mm. This work has important implications for the development of the MP when operating in transmission mapping mode.

The biannual MMND (former MMD) - IPCT workshops was founded in collaboration between the Centre for Medical Radiation Physics, University of Wollongong and the Memorial Sloan Kettering Cancer Center (MSKCC) in 2001 and has become an important international multidisciplinary forum for the discussion of advanced quality assurance (QA) dosimetry technology for radiation therapy and space science, as well as advanced technologies for clinical cancer treatment.

The new era of intra-fraction dose tracking in radiation therapy delivery demands new dosimetry methods, whereby a moving frame of reference as a function of time may be required. This introduces a new paradigm into radiation therapy dose verification. The term we propose to describe this is dynamic dosimaging, which by our definition is tracking the location of a dosimeter array in real time during on-line radiation dose acquisition.

A diamond based microdosimeter prototype featuring a 3D lateral electrode structure was created using laser ablation and active brazing alloys and characterised by means of ion beam induced charge collection measurements and finite element analysis, using Synopsys TCAD simulation package.

A Geant4 Monte Carlo simulation study was carried out to characterise a novel silicon strip detector, the Dose Magnifying Glass (DMG), for use in proton therapy Quality Assurance. We investigated the possibility to use DMG to determine the energy of the incident proton beam. The advantages of DMG are quick response, easy operation and high spatial resolution. In this work we theoretically proved that DMG can be used for QA in the determination of the energy of the incident proton beam, for ocular and prostate cancer therapy. The study was performed by means of Monte Carlo simulations Experimental measurements are currently on their way to confirm the results of this simulation study.

The high spatial and temporal resolution 2D monolithic silicon detector arrays M512 and DUO for quality assurance (QA) in real time motion adaptive radiotherapy (ART) have been developed. The DUO array possesses a spatial resolution of 0.2 mm and has demonstrated agreement within 5% with EBT3 film measurements of 6MV linac beam profiles for field sizes 1 × 1 cm2 and SRS cone diameter 0.5 cm. Dynamic characterisation of the M512 for QA in real time ART evaluated the performance of M512 for small fields while the detector experiences periodic motion. It was demonstrated with M512 that MLC tracking with Calypso electromagnetic array compensates for the periodic motion and improves the agreement between static and dynamic beam profiles for field size 1 × 1 cm2 from within 75% in the penumbra to within 11% agreement. The dynamic profile is returned to a similar distribution as the static case.

In vivo dosimetry (IVD) is an excellent mode of treatment verification and detection of possible overexposures. A feasibility study was conducted to evaluate a proposed IVD procedure for gynecological HDR brachytherapy procedure quality assurance. MO. Skin dosimeters were selected due to their small size and capability of measuring steep dose gradients, such as those relevant in HDR brachytherapy procedures. Two in-phantom experiments measuring dose with MO. Skins at the position simulating the rectal wall were conducted employing a cylindrical single channel applicator and a multichannel applicator. Three MO. Skins were incorporated onto a rectal catheter, which was then attached to the applicator, separated by a small wooden plaque, simulating the vaginal to rectal wall distance and fixing catheter position. This setup was inserted into a water phantom and three treatment plans prescribing 300 cGy to 3 different targets were assigned with various dose distributions. Each treatment was administered three times, and doses measured by the MO. Skins were recorded. Doses measured by the MO. Skins were within 5% of the dose determined by the treatment planning system (TPS), ranging between 208 and 332 cGy, depending on dosimeter position on the rectal catheter. The overall average dose difference between measured and TPS values was 2.09% ± 1.15% (ranging between 0.83 and 4.27%, with measured values always higher than TPS dose), subdivided in 1.40 ± 0.37% and 2.79 ± 1.27% for single and multichannel applicator experiments, respectively. An overall dose agreement between the TPS and measured values, detector reproducibility, and practicality of the rectal catheter demonstrated the suitability of the proposed method for in vivo real time QA purposes in gynecological HDR brachytherapy.

PURPOSE: Nowadays, there are many different applications that use small fields in radiotherapy treatments. The dosimetry of small radiation fields is not trivial due to the problems associated with lateral disequilibrium and source occlusion and requires reliable quality assurance (QA). Ideally such a QA tool should provide high spatial resolution, minimal beam perturbation and real time fast measurements. Many different types of silicon diode arrays are used for QA in radiotherapy; however, their application in small filed dosimetry is limited, in part, due to a lack of spatial resolution. The Center of Medical Radiation Physics (CMRP) has developed a new generation of a monolithic silicon diode array detector that will be useful for small field dosimetry in SRS/SRT. The objective of this study is to characterize a monolithic silicon diode array designed for dosimetry QA in SRS/SRT named DUO that is arranged as two orthogonal 1D arrays with 0.2 mm pitch. METHODS: DUO is two orthogonal 1D silicon detector arrays in a monolithic crystal. Each orthogonal array contains 253 small pixels with size 0.04 x 0.8 mm2 and three central pixels are with a size of 0.18 x 0.18 mm2 each. The detector pitch is 0.2 mm and total active area is 52 x 52 mm2 . The response of the DUO silicon detector was characterized in terms of dose per pulse, percentage depth dose, and spatial resolution in a radiation field incorporating high gradients. Beam profile of small fields and output factors measured on a Varian 2100EX LINAC in a 6 MV radiation fields of square dimensions and sized from 0.5 x 0.5 cm2 to 5 x 5 cm2. The DUO response was compared under the same conditions with EBT3 films and an ionization chamber. RESULTS: The DUO detector shows a dose per pulse dependence of 5% for a range of dose rates from 2.7 x 10-4 to 1.2 x 10-4 Gy/pulse and 23% when the rate is further reduced to 2.8 x 10-5 Gy/pulse. The percentage depth dose measured to 25 cm depth in solid water phantom beyond the surf

This work aims to characterize a proton pencil beam scanning (PBS) and passive double scattering (DS) systems as well as to measure parameters relevant to the relative biological effectiveness (RBE) of the beam using a silicon on insulator (SOI) microdosimeter with well-defined 3D sensitive volumes (SV). The dose equivalent downstream and laterally outside of a clinical PBS treatment field was assessed and compared to that of a DS beam.

Purpose This study aims to investigate the 2D monolithic silicon diode array size of 52 × 52 mm2 (MP512) angular response. An angular correction method has been developed that improves the accuracy of dose measurement in a small field. Methods The MP512 was placed at the center of a cylindrical phantom, irradiated using 6 MV and 10 MV photons and incrementing the incidence of the beam angle in 15° steps from 0° to 180°, and then in 1° steps between 85° and 95°. The MP512 response was characterized for square field sizes varying between 1 × 1 cm2 and 10 × 10 cm2. The angular correction factor was obtained as the ratio of MP512 response to EBT3 film measured doses as a function of the incidence angle (Ɵ) and was normalized at 0° incidence angle. Beam profiles of the corrected MP512 responses were compared with the EBT3 responses to verify the effectiveness of the method adopted. Results The intrinsic angular dependence of the MP512 shows maximum relative deviation from the response normalized to 0° of 18.5 ± 0.5% and 15.5 ± 0.5% for 6 MV and 10 MV, respectively, demonstrating that the angular response is sensitive to the energy. In contrast, the variation of angular response is less affected by field size. Comparison of cross-plane profiles measured by the corrected MP512 and EBT3 shows an agreement within ±2% for all field sizes when the beams irradiated the array at 0°, 45°, 135°, and 180° angles of incidence from the normal to the detector plane. At 90° incidence, corresponding to a depth dose measurement, up to a 6% discrepancy was observed for a 1 × 1 cm2 field of 6 MV. Conclusion An angular correction factor can be adopted for small field sizes. Measurements discrepancies could be encountered when irradiating with very small fields parallel to the detector plane. Using this approach, the MP512 is shown to be a suitable detector for 2D dose mapping of small field size photon beams.

Purpose BrachyView is a novel in-body imaging system which aims to provide LDR brachytherapy seeds position reconstruction within the prostate in real-time. The first prototype is presented in this study: the probe consists of a gamma camera featuring three single cone pinhole collimators embedded in a tungsten tube, above three, high resolution pixelated detectors (Timepix). Methods The prostate was imaged with a TRUS system using a sagittal crystal with a 2.5 mm slice thickness. Eleven needles containing a total of thirty 0.508 U125I seeds were implanted under ultrasound guidance. A CT scan was used to localise the seed positions, as well as provide a reference when performing the image co-registration between the BrachyView coordinate system and the TRUS coordinate system. An in-house visualisation software interface was developed to provide a quantitative 3D reconstructed prostate based on the TRUS images and co-registered with the LDR seeds in situ. A rigid body image registration was performed between the BrachyView and TRUS systems, with the BrachyView and CT-derived source locations compared. Results The reconstructed seed positions determined by the BrachyView probe showed a maximum discrepancy of 1.78 mm, with 75% of the seeds reconstructed within 1 mm of their nominal location. An accurate co-registration between the BrachyView and TRUS coordinate system was established. Conclusions The BrachyView system has shown its ability to reconstruct all implanted LDR seeds within a tissue equivalent prostate gel phantom, providing both anatomical and seed position information in a single interface.

Microbeam radiation therapy (MRT) is a promising radiotherapy modality that uses arrays of spatially fractionated micrometre-sized beams of synchrotron radiation to irradiate tumours. Routine dosimetry quality assurance (QA) prior to treatment is necessary to identify any changes in beam condition from the treatment plan, and is undertaken using solid homogeneous phantoms. Solid phantoms are designed for, and routinely used in, megavoltage X-ray beam radiation therapy. These solid phantoms are not necessarily designed to be water-equivalent at low X-ray energies, and therefore may not be suitable for MRT QA. This work quantitatively determines the most appropriate solid phantom to use in dosimetric MRT QA. Simulated dose profiles of various phantom materials were compared with those calculated in water under the same conditions. The phantoms under consideration were RMI457 Solid Water (Gammex-RMI, Middleton, WI, USA), Plastic Water (CIRS, Norfolk, VA, USA), Plastic Water DT (CIRS, Norfolk, VA, USA), PAGAT (CIRS, Norfolk, VA, USA), RW3 Solid Phantom (PTW Freiburg, Freiburg, Germany), PMMA, Virtual Water (Med-Cal, Verona, WI, USA) and Perspex. RMI457 Solid Water and Virtual Water were found to be the best approximations for water in MRT dosimetry (within ±3% deviation in peak and 6% in valley). RW3 and Plastic Water DT approximate the relative dose distribution in water (within ±3% deviation in the peak and 5% in the valley). PAGAT, PMMA, Perspex and Plastic Water are not recommended to be used as phantoms for MRT QA, due to dosimetric discrepancies greater than 5%.

Purpose To investigate the effect on surface dose, as a function of different field sizes and distances from the solid water phantom to transmission detector (Dsd), of using the monolithic silicon detector MP512T in transmission mode. Methods The influence of operating the MP512T in transmission mode on the surface dose of a phantom for SSD 100cm was evaluated by using a Markus IC. The MP512T was fixed to an adjustable stand holder and was positioned at different Dsd, ranging from 0.3 to 24 cm. For each Dsd, measurements were carried out for irradiation field sizes of 5 × 5cm2, 8 × 8 cm2 and 10 × 10 cm2. Measurements were obtained under two different operational setups, (i) with the MP512T face-up and (ii) with the MP512T face-down. In addition, the transmission factors for the MP512T and the printed circuit board were only evaluated using a Farmer IC. Results For all Dsd and all field sizes, the MP512T led to the surface dose increasing by less than 25% when in the beam. For Dsd >18 cm the surface dose increase is less than 5%, and negligible for field size 5 × 5 cm2. The difference in the surface dose perturbation for the MP512T operating face up or operating face down is negligible (sd and field sizes. Conclusion The study demonstrated that positioning the MP512T in air between the Linac head and the phantom produced negligible perturbation of the surface dose for Dsd >18 cm, and was completely transparent for 6 MV photon beams.

Radiation therapy is rapidly evolving toward the delivery of higher dose rates to improve cancer treatment. In vitro experiments were performed to investigate the response of 9L and MCF-7 cancer cell lines, exposed to 10 MV X-ray radiations. Up to 8 Gy was delivered at a dose-rate of 50 cGy/min compared to 5 Gy/min. The data obtained emphasizes the importance of taking into account not only the physical, but also the radiobiological parameters, when planning a particular cancer treatment.