Centre For Medical Radiation Physics Research Articles

Introduction and implementation of the CMRP radiodosimeter — a novel wireless microdosimetry system

Microdosimetry is a useful method to evaluate the relative biological effectiveness (RBE) as well as dose equivalent of any mixed radiation field without prior knowledge of type of charged particles and their spectra. The need of portable, user friendly devices for microdosimetric Quality Assurance measurements in particle therapy are greatly preferable to avoid sophisticated setup and time-consuming data analysis.Currently, the ability to perform microdosimetric measurements is restricted to those with extensive prior knowledge of the electronics involved and their experimental setup.The Centre for Medical Radiation Physics (CMRP) has developed a compact microdosimetric system named Radiodosimeter - a novel acquisition system that combines both wireless communication and plug-and-play design to provide a device that can be used with minimal setup. The system is compatible with current CMRP MicroPlus probe technology. The Radiodosimeter communicates with the client computer via Wi-Fi, allowing remote management and monitoring of acquisitions.The system was bench-marked against the standard microdosimetric setup at Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan and was found to have the same response. Several redundancy methods were demonstrated such as continuing an acquisition following disconnection from the client software and the ability to connect through different Wi-Fi modes (WPA2 Personal/Enterprise).These features prove that the Radiodosimeter can operate independently of a client computer, indicating its potential to be used as a portable device for personal monitoring in mixed radiation fields, including for microdosimetric quantity verification predicted by Treatment Planning Software in particle therapy.

Silicon 3D Microdosimeters for Advanced Quality Assurance in Particle Therapy

The Centre for Medical Radiation Physics introduced the concept of Silicon On Insulator (SOI) microdosimeters with 3-Dimensional (3D) cylindrical sensitive volumes (SVs) mimicking the dimensions of cells in an array. Several designs of high-definition 3D SVs fabricated using 3D MEMS technology were implemented. 3D SVs were fabricated in different sizes and configurations with diameters between 18 and 30 µm, thicknesses of 2–50 µm and at a pitch of 50 µm in matrices with volumes of 20 × 20 and 50 × 50. SVs were segmented into sub-arrays to reduce capacitance and avoid pile up in high-dose rate pencil beam scanning applications. Detailed TCAD simulations and charge collection studies in individual SVs have been performed. The microdosimetry probe (MicroPlus) is composed of the silicon microdosimeter and low-noise front–end readout electronics housed in a PMMA waterproof sheath that allows measurements of lineal energies as low as 0.4 keV/µm in water or PMMA. Microdosimetric quantities measured with SOI microdosimeters and the MicroPlus probe were used to evaluate the relative biological effectiveness (RBE) of heavy ions and protons delivered by pencil-beam scanning and passive scattering systems in different particle therapy centres. The 3D detectors and MicroPlus probe developed for microdosimetry have the potential to provide confidence in the delivery of RBE optimized particle therapy when introduced into routine clinical practice.

Response of SOI microdosimeter in fast neutron beams: experiment and Monte Carlo simulations.

In this study, Monte Carlo codes, Geant4 and MCNP6, were used to characterize the fast neutron therapeutic beam produced at iThemba LABS in South Africa. Experimental and simulation results were compared using the latest generation of Silicon on Insulator (SOI) microdosimeters from the Centre for Medical Radiation Physics (CMRP). Geant4 and MCNP6 were able to successfully model the neutron gantry and simulate the expected neutron energy spectrum produced from the reaction by protons bombarding a 9Be target. The neutron beam was simulated in a water phantom and its characteristics recorded by the silicon microdosimeters; bare and covered by a 10B enriched boron carbide converter, at different positions. The microdosimetric quantities calculated using Geant4 and MCNP6 are in agreement with experimental measurements. The thermal neutron sensitivity and production of 10B capture products in the p+ boron-implanted dopant regions of the Bridge microdosimeter is investigated. The obtained results are useful for the future development of dedicated SOI microdosimeters for Boron Neutron Capture Therapy (BNCT). This paper provides a benchmark comparison of Geant4 and MCNP6 capabilities in the context of further applications of these codes for neutron microdosimetry.

In-field and out-of-field microdosimetric characterisation of a 62 MeV proton beam at CATANA.

A 5 and 10 μm thin silicon on insulator (SOI) 3D mushroom microdosimeter was used to characterize both the in-field and out-of-field of a 62 MeV proton beam. The SOI mushroom microdosimeter consisted of an array of cylindrical sensitive volumes (SVs), developed by the Centre for Medical Radiation Physics, University of Wollongong, was irradiated with 62 MeV protons at the CATANA (Centro di AdroTerapia Applicazioni Nucleari Avanzate) facility in Catania, Italy, a facility dedicated to the radiation treatment of ocular melanomas. Dose mean lineal energy, ( ), values were obtained at various depths in PMMA along a pristine and spread out Bragg peak (SOBP). The measured microdosimetric spectra at each position were then used as inputs into the modified Microdosimetric Kinetic Model (MKM) to derive the RBE for absorbed dose in a middle of the SOBP 2Gy (RBED ). Microdosimetric spectra were obtained with both the 5 and 10 μm 3D SOI microdosimeters, with a focus on the distal part of the BP. The in-field and out-of-field measurement configurations along the Bragg curve were modeled in Geant4 for comparison with experimental results. Lateral out-of-field measurements were performed to study secondary particles' contribution to normal tissue's dose, up to 12 mm from the edge of the beam field, and quality factor and dose equivalent results were obtained. Comparison between experimental and simulation results showed good agreement between one another for both the pristine and SOBP beams in terms of and RBED. Though a small discrepancy between experiment and simulation was seen at the entrance of the Bragg curve, where experimental results were slightly lower than Geant4. The dose equivalent value measured 12 mm from the edge of the target volume was 1.27 ± 0.15 mSv/Gy with a value of 2.52 ± 0.30, both of which agree within uncertainty with Geant4 simulation. These results demonstrate that SOI microdosimeters are an effective tool to predict RBED in-field as well as dose equivalent monitoring out-of-field to provide insight to probability of second cancer generation.

Modelling of protons spectra encountered in space using medical accelerator and its microdosimetric characterization

Radiation environments in space are mainly composed of protons coming from the Galactic Cosmic Rays (GCRs) pervading the universe, the Solar Particle Events (SPEs) resulting from solar flares and coronal mass ejections, and the two Van Allen Belts surrounding the Earth due to the presence of the geomagnetic field trapping charged particles. Their wide spectra of energies up to hundreds of GeV imply diverse radiobiological effects to astronauts and radiation damage to electronics in the spacecraft. Even if lower in abundance, heavy ions such as He, C, O, Si, Fe are present in space and constitute an even bigger hazard due to their high penetrability and high linear energy transfer (LET). Most irradiation facilities available for research and testing worldwide provide usually only monoenergetic beams of high-energy protons or other heavier particles limiting studies of radiobiological effects and effects on electronics to a set of discrete energies.This paper introduces a procedure where a proton fluence spectra of interest for space radiation protection, previously generated by Monte Carlo simulations was delivered using a clinical proton therapy accelerator.Particularly, it reports the first results of modelling a proton radiation field in space in the energy range from 70 to 230 MeV during a single experimental session by programming a treatment planning system (TPS) to deliver required proton irradiation energies. Moreover, the angular distribution of the proton irradiation field has been varied to reproduce the isotropic exposure experienced by humans in space. The obtained proton radiation field was characterized using a 3D sensitive volume SOI microdosimeter developed by the Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia.

Monte Carlo implementation of new algorithms for the evaluation of averaged-dose and -track linear energy transfers in 62 MeV clinical proton beams

We exploited the power of the Geant4 Monte Carlo toolkit to study and validate new approaches for the averaged linear energy transfer (LET) calculation in 62 MeV clinical proton beams. The definitions of the averaged LET dose and LET track were extended, so as to fully account for the contribution of secondary particles generated by target fragmentation, thereby leading to a more general formulation of the LET total. Moreover, in the proposed new strategies for the LET calculation, we minimised the dependencies in respect to the transport parameters adopted during the Monte Carlo simulations (such as the production cut of secondary particles, voxel size and the maximum steplength). The new proposed approach was compared against microdosimetric experimental spectra of clinical proton beams, acquired at the Italian eye proton therapy facility of the Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare (INFN-LNS, Catania, I) from two different detectors: a mini-tissue equivalent proportional chamber (TEPC), developed at the Legnaro National Laboratories of the National Institute for Nuclear Physics (LNL-INFN) and a silicon-on-insulator (SOI) microdosimeter with 3D sensitive volumes developed by the Centre for Medical Radiation Physics of Wollongong University (CMRP-UoW). A significant increase of the LET in the entrance region of the spread out Bragg peak (SOBP) was observed, when the contribution of the generated secondary particles was included in the calculation. This was consistent with the experimental results obtained.

Preface

Micro-Mini & Nano Dosimetry and Innovative Technologies in Radiation Oncology - MMND ITRO 2020 The biannual Micro-Mini & Nano Dosimetry and Innovative Technologies in Radiation Oncology (MMND ITRO 2020) international conferences organized by the Centre for Medical Radiation Physics (CMRP), University of Wollongong jointly with Memorial Sloan Kettering Cancer Center (MSKCC), New York were hold on the 10th-16th February 2020 at the Novotel Wollongong Northbeach, Wollongong, NSW, Australia. During MMND ITRO 2020 we celebrated 20th Anniversary of these biannual workshops.Continuing the series of biennial meetings, the Mini- Micro- Nano- Dosimetry (MMND) conference brought together international and Australian radiation oncologists, medical physicists, radiation scientists and nanomedicine experts. Talks were focused on new achievements in radiobiology of radiation therapy including particle therapy and synchrotron MRT, diffused alpha emitters radiation therapy (DaRT) in combination with immunotherapy, radiomics and artificial intelligence as applied to radiation therapy and imaging, advanced dosimetry in radiotherapy, diagnostic imaging and diagnostic radiology for physicists. Special half-day sessions were led by experts from MSKCC on New Technologies in Brachytherapy by Prof. Michael Zelefsky MD, and Radiomics and Machine Learning Models by Prof. Joseph Deasy PhD.Innovative Technologies in Radiation Oncology (ITRO) led by Dr Josh Yamada, MD was devoted to the clinical implementation of new technologies in X-ray therapy, brachytherapy and particle therapy. ITRO 2020 focused on integrating advanced imaging into radiation therapy including MRI guided radiotherapy, MRI for tissue radiation response prediction, imaging in prediction of patient response to immunotherapy, SBRT, SRS, hypofractionation and particle therapy as well as applications of radiomics and artificial intelligence in radiation oncology and radiology.

Study on the RBE estimation for carbon beam scanning irradiation using a solid-state microdosimeter.

The purpose of this study was to study the field size effect on the estimated Relative Biological Effectiveness (RBE) for carbon scanning beam irradiation. A silicon-on-insulator (SOI) microdosimeter system developed by the Centre for Medical Radiation Physics, University of Wollongong, Australia, was used for lineal-energy measurements (microdosimetric quantity). The RBE values were derived based on the modified microdosimetric kinetic model (MKM) at different depths in a water phantom in the scanning carbon beam for various scanned areas. Our study shows that the difference in RBE values derived from the SOI microdosimeter measurements with the MKM model and from the Treatment Planning System (TPS). The difference of the RBE values is within 6.5 % at the peak point of the spread-out Bragg Peak (SOBP) region. Compared to the spot-beam, RBE values obtained in the scanned-beam with a larger scanned area of 1.0×1.0cm2 have better agreement with which estimated by the TPS. This study shows the possibility of using the SOI microdosimeter system as a quality assurance (QA) tool for RBE evaluation in carbon-pencil beam scanning radiotherapy.

Characterization of 3-D-Mesa Silicon Single Strip Detectors for Use in Synchrotron Microbeam Radiation Therapy

The Centre for Medical Radiation Physics (CMRP) has designed and produced novel n-type silicon single strip detectors (SSDs) for use in dosimetry of synchrotron-based microbeam radiation therapy (MRT). In order to address the challenges of dosimetry and quality assurance of these beams, a detector is required with micron-scale spatial resolution, real-time read-out, large dynamic range, and significant radiation hardness. The CMRP first-generation 3-D-Mesa SSD is fabricated in n-SOI technology and involves plasma etching to produce a 10 $\times $ 36 $\times $ 250 $\mu \text{m}^{3}$ sensitive volume (SV) or a 10 $\times $ 22.5 $\times $ 250 ${\mu }\text{m}^{3}$ SV with all surrounding silicon above the insulating layer removed. The 3-D-Mesa has undergone full electrical characterization and a charge collection study, supported by TCAD simulations to model electric field in the device. The optimal operating bias was found to be −2 V, which produces a dark current of less than 1 nA and 100% charge collection efficiency within the SV. Charge collection is observed at greater biases from the silicon bridge under the Al bus that electrically connects the SV of the SSD to the readout pad. The reasons for this are discussed and will be addressed in the next generation of the 3-D-Mesa SSD.

X-Tream dosimetry of synchrotron radiation with the PTW microDiamond

In this study, we demonstrate that the X-Tream dosimetry system developed by the Centre for Medical Radiation Physics can be used with both commercial and non-commercial dosimeters. A custom adaptor was constructed to connect the PTW microdiamond to the X-Tream DAQ. This allowed for the measurements of continuous depth dose curves, broad beam and microbeam profiles. The X-Tream system enables real time measurement of the instantaneous dose rate of synchrotron generated radiation with the PTW microDiamond. Finally, measurements undertaken in this study demonstrate that the X-Tream system is able to mitigate the alignment issue that has previously hampered the uptake of the PTW microdiamond in clinical quality assurance for small field dosimetry.

Modelling of the Silicon-On-Insulator microdosimeter response within the International Space Station for astronauts’ radiation protection

Astronauts are exposed to high-energy cosmic radiation which may have harmful health effects. At the altitude of the International Space Station (ISS), the main radiation sources are Galactic Cosmic Rays (GCRs), Solar Particle Events (SPEs) and trapped protons of the Van Allen Belts. The radiation field mainly consists of protons, helium nuclei and heavy ions with energies up to hundreds of GeV/n. A powerful approach to determine the effect of space radiation on astronauts is microdosimetry. The Centre for Medical Radiation Physics is active in the development of Silicon-On-Insulator (SOI) microdosimeters, as an alternative to Tissue Equivalent Proportional Counters (TEPCs) for radiation protection purposes. SOI microdosimeters are portable and do not require a high-voltage power supply. They consist of a matrix of silicon Sensitive Volumes (SV), which mimic the dimensions of biological cells.In this study, we investigated for the first time the response of the 3D “Mushroom” microdosimeter, a type of SOI microdosimeter in the Columbus module of the ISS. Tissue-equivalent microdosimetric spectra of GCRs, SPEs, and trapped protons were obtained to estimate the dose equivalent delivered to the astronauts. Results demonstrate a non-negligible production of secondary particles due to the propagation of space radiation through the wall of the Columbus and the microdosimeter. A number of heavy ions were detected with high lineal energies, these events pose a significant hazard in terms of radiation protection.Moreover, the dose evaluation shows a good agreement with experimental data found in the literature, confirming the suitability of our Geant4 model and the feasibility of using the SOI microdosimeter for ISS astronauts’ personal dosimetry.

2D monolithic silicon-diode array detectors in megavoltage photon beams: does the fabrication technology matter? A medical physicist's perspective.

A family of prototype 2D monolithic silicon-diode array detectors (MP512, Duo, Octa) has been proposed by the Centre for Medical Radiation Physics, University of Wollongong (Australia) for relative dosimetry in small megavoltage photon beams. These detectors, which differ in the topology of their 512 sensitive volumes, were originally fabricated on bulk p-type substrates. More recently, they have also been fabricated on epitaxial p-type substrates. In the literature, their performance has been individually characterized for quality assurance (QA) applications. The present study directly assessed and compared that of a MP512-bulk and that of a MP512-epitaxial in terms of radiation hardness, long-term stability, response linearity with dose, dose per pulse and angular dependence. Their measurements of output factors, off-axis ratios and percentage depth doses in square radiation fields collimated by the jaws and produced by 6MV and 10MV flattened photon beams were then benchmarked against those by commercially available detectors. The present investigation was aimed at establishing, from a medical physicist's perspective, how the bulk and epitaxial fabrication technologies would affect the implementation of the MP512s into a QA protocol. Based on results, the MP512-epitaxial would offer superior radiation hardness, long-term stability and achievable uniformity and reproducibility of the response across the 2D active area.

INVESTIGATING VARIABLE RBE IN A 12C MINIBEAM FIELD WITH MICRODOSIMETRY AND GEANT4.

An experimental and simulation-based study was performed on a 12C ion minibeam radiation therapy (MBRT) field produced with a clinical broad beam and a brass multi-slit collimator (MSC). Silicon-on-insulator (SOI) microdosimeters developed at the Centre for Medical Radiation Physics (CMRP) with micron sized sensitive volumes were used to measure the microdosimetric spectra at varying positions throughout the MBRT field and the corresponding dose-mean lineal energies and RBE for 10% cell survival (RBE10) were calculated using the modified Microdosimetric Kinetic Model (MKM). An increase in the average RBE10 of ∼30% and 10% was observed in the plateau region compared to broad beam for experimental and simulation values, respectively. The experimental collimator misalignment was determined to be 0.7° by comparison between measured and simulated microdosimetric spectra at varying collimator angles. The simulated dose-mean lineal energies in the valley region between minibeams were found to be higher on average than in the minibeams due to higher LET particles being produced in these regions from the MSC. This work presents the first experimental microdosimetry measurements and characterisation of the local biological effectiveness in a MBRT field.

Simulation of cosmic radiation spectra for personal microdosimetry at the International Space Station’s altitude

Latest researches predict the cosmic rays exposure during long space missions outside the Earth’s geomagnetic sphere, as to the Moon and Mars, can double the cancer risk. The minimization of risk associated with radiation exposure in the Low Earth Orbit (LEO) is of great interest for astronauts of the International Space Station (ISS). This risk is due to radiation hazard and can be predicted by measurement of the dose equivalent produced by the radiation environment inside of the spacecraft. Since more than 15 years ago, the Centre For Medical Radiation Physics (CMRP), University of Wollongong, is developing silicon based microdosimeters as alternative solution to Tissue Equivalence Proportional Counters, for dose equivalent determination in the context of astronauts radiation protection. This work describes a Geant4-based study characterising the radiation environment encountered by astronauts inside the ISS. In particular, the energy spectra of different components of the cosmic radiation field, as Galactic Cosmic Rays (GCR), trapped protons and electrons and Solar Proton Event (SPE), has been simulated outside and inside the Columbus module where astronauts live. The simulated radiation environment inside of the ISS will be used to model the response of the 3D Mushroom Silicon On Insulator (SOI) microdosimeter recently developed at CMRP.

Preliminary epi-diode characterization for HDR brachytherapy quality assurance

High Dose Rate vaginal brachytherapy for endometrial cancer has evolved from simple single-channel (i.e. cylindrical applicator) deliveries to treatments involving several channels (i.e. multichannel applicator) for the radiotherapy source to dwell, increasing the complexity of the dose distribution, and allowing more space for potential errors. For this reason real-time treatment verification has gained a greater importance than ever before, and more methods need to be developed in order to provide assurance that the dose delivery has been carried out as intended by the hospital staff. P-type silicon epi diodes have been designed at the Centre for Medical Radiation Physics (CMRP) in Australia to suit the specific needs of HDR BT, and characterized in the clinical BT facility of the Fondazione IRCCS (INT) in Italy. They have shown great potential for BT treatment verification in real time due to their radiation hardness, dose rate independence, flexibility in physical design, and ability to monitor the treatment at a 1-kHz readout frequency. Their dynamic range has been determined as ±17 to ±20 mm and dwell time calculation accuracy of > 0.1 s has been shown. If placed on the same longitudinal plane of a treatment accessory, these detectors would enable coverage of about 40 mm for source position and dwell time tracking. Respective detector positioning at (0, +3, −3 mm) would extend this range to 45-50 mm, depending on the catheter location, proving to be sufficient for the majority of treatment cases. Further studies are encouraged to develop diodes with a wider dynamic range.

Micro-Mini & Nano Dosimetry (MMND) 2018

Introduction to Mini-Micro & Nano Dosimetry and Innovative Technologies in Radiation Oncology (MMNDITRO) 2018The biannual Micro-Mini & Nano Dosimetry and Innovative Technologies in Radiation Oncology (MMNDITRO2018) international workshops, traditionally organized by the Centre for Medical Radiation Physics (CMRP), University of Wollongong jointly with the Memorial Sloan Kettering Cancer Center (MSKCC), New York were held from 6-11 February 2018 at the Mantra Mooloolaba Beach Resort, Mooloolaba, Queensland, Australia.Continuing our series of biennial meetings, the MMND 2018 workshop, from 6-8 February 2018, brought together both Australian and international radiation oncologists, medical physicists, radiation scientists and nanomedicine experts to discuss advances in radiation oncology modalities and radiation dosimetry technologies for quality assurance in radiation therapy, radiobiological optimisation of treatments, and other relevant technologies, to further improve clinical outcomes of radiation therapy. For the first time in the MMND workshop series, a special brachytherapy day, led by Dr Michael Zelefsky MD, was held.The ITRO 2018 workshop, from 10-11 February, was devoted to clinical implementation of new technologies in X-ray therapy, brachytherapy and particle therapy. A special focus of ITRO was Integrating biology and technology including immunotherapy, SBRT, hypofractionation, particle therapy, SRS, Integration of multi-parametric MRI into radiotherapy and other approaches on the way to personalised treatments.For more information about MMNDITRO2018 program visit https://mmnditro2018.dryfta.com/en/Anatoly Rozenfeld PhDDr Joshija (Josh) Yamada MD

Evolution of Diamond based Microdosimetry

The requirements for solid state micro- dosimetry particularly within the context of medical and space environments necessitate a tissue equivalent and radiation hard material, for which diamond is uniquely suited. An overview of the current status of diamond based microdosimetry is given. This overview will explore previous and current technologies developed by the Centre for Medical Radiation Physics (CMRP). The overview will analyse technologies in terms of their advantages and disadvantages within the context of microdosimetry. Using this as a basis, recommendations with respect to fabri- cation methodologies/techniques are provided in order to direct the course and progress of development so as to achieve true diamond based microdosimetry.

SOI Thin Microdosimeter Detectors for Low-Energy Ions and Radiation Damage Studies

The responses of two silicon on insulator (SOI) 3-D microdosimeters developed by the Centre for Medical Radiation Physics were investigated with a range of different low energy ions, with high linear energy transfer (LET). The two microdosimeters n-SOI and p-SOI were able to measure the LET of different ions including 7Li, 12C, 16O, and 48Ti with ranges below $350~\mu \text{m}$ in silicon. No plasma effects were seen in the SOI microdosimeters when irradiated with the high LET ions. A Monte Carlo simulation using Geant4 was compared to the experimental measurements, whereby some discrepancies were observed for heavier ions at lower energies. This discrepancy can be partly attributed to uncertainties in the thickness of the energy degraders and overlayers of the devices. The microdosimetric measurements of low energy 16O ions were obtained and compared to a therapeutic 16O ion beam. The radiation hardness of the two devices was studied using the ion beam induced charge collection technique. Both types of the microdosimeters when biased had no essential changes in charge collection efficiency in the sensitive volume after irradiation with low energy ions.

In-field and out-of-file application in 12C ion therapy using fully 3D silicon microdosimeters

This paper presents recent development of Silicon on Insulator (SOI) detectors for microdosimetry at the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong. A new CMRP SOI microdosimeter design, the 3D mushroom microdosimeter is presented. Modification of SOI design and changes to the fabrication processes have led to improved definition of the microscopic sensitive volumes (SV), and thus to better modelling of the deposition of ionizing energy in a biological cell. The electrical and charge collection properties of the devices have been presented in previous works. In this study, the response of the microdosimeters in monoenergetic and spread out Bragg peak therapeutic 12C ion beam at Heavy Ion Medical Accelerator in Chiba (HIMAC, Japan) are presented. Derived relative biological effectiveness (RBE) in 12C ion radiation therapy matches the tissue equivalent proportional counter (TEPC) well, along with outstanding spatial resolution. The use of SOI technology in experimental microdosimetry offers simplicity (no gas system or HV supply), high spatial resolution, low cost, high count rates capabilities for beam characterisation and quality assurance (QA) in charged particle therapy.

A novel high-resolution 2D silicon array detector for small field dosimetry with FFF photon beams

PurposeFlattening filter free (FFF) beams are increasingly being considered for stereotactic radiotherapy (SRT). For the first time, the performance of a monolithic silicon array detector under 6 and 10 MV FFF beams was evaluated. The dosimeter, named “Octa” and designed by the Centre for Medical Radiation Physics (CMRP), was tested also under flattened beams for comparison. MethodsOutput factors (OFs), percentage depth-dose (PDD), dose profiles (DPs) and dose per pulse (DPP) dependence were investigated. Results were benchmarked against commercially available detectors for small field dosimetry. ResultsThe dosimeter was shown to be a ‘correction-free’ silicon array detector for OFs and PDD measurements for all the beam qualities investigated. Measured OFs were accurate within 3% and PDD values within 2% compared against the benchmarks. Cross-plane, in-plane and diagonal DPs were measured simultaneously with high spatial resolution (0.3 mm) and real time read-out. A DPP dependence (24% at 0.021 mGy/pulse relative to 0.278 mGy/pulse) was found and could be easily corrected for in the case of machine specific quality assurance applications. ConclusionsResults were consistent with those for monolithic silicon array detectors designed by the CMRP and previously characterized under flattened beams only, supporting the robustness of this technology for relative dosimetry for a wide range of beam qualities and dose per pulses. In contrast to its predecessors, the design of the Octa offers an exhaustive high-resolution 2D dose map characterization, making it a unique real-time radiation detector for small field dosimetry for field sizes up to 3 cm side.