A simulation study of BrachyShade, a shadow-based internal source tracking system for HDR prostate brachytherapy

This paper presents a simulation study of BrachyShade, a proposed internal source-tracking system for real time quality assurance in high dose rate prostate brachytherapy. BrachyShade consists of a set of spherical tungsten occluders located above a pixellated silicon photodetector. The source location is estimated by minimising the mean squared error between a parametric model of the shadow image and acquired images of the shadows projected on the detector plane. A novel algorithm is finally employed to correct the systemic error resulting from Compton scattering in the medium. The worst-case error obtained with BrachyShade for a 13.5 ms image acquisition is less than 1.3 mm in the most distant part of the treatment volume, while for 75% of source locations an error of less than 0.42 mm was achieved

Opportunistic dose amplification for proton and carbon ion therapy via capture of internally generated thermal neutrons

This paper presents Neutron Capture Enhanced Particle Therapy (NCEPT), a method for enhancing the radiation dose delivered to a tumour relative to surrounding healthy tissues during proton and carbon ion therapy by capturing thermal neutrons produced inside the treatment volume during irradiation. NCEPT utilises extant and in-development boron-10 and gadolinium-157-based drugs from the related field of neutron capture therapy. Using Monte Carlo simulations, we demonstrate that a typical proton or carbon ion therapy treatment plan generates an approximately uniform thermal neutron field within the target volume, centred around the beam path. The tissue concentrations of neutron capture agents required to obtain an arbitrary 10% increase in biological effective dose are estimated for realistic treatment plans, and compared to concentrations previously reported in the literature. We conclude that the proposed method is theoretically feasible, and can provide a worthwhile improvement in the dose delivered to the tumour relative to healthy tissue with readily achievable concentrations of neutron capture enhancement drugs

The evolution in the stellar mass of Brightest Cluster Galaxies over the past 10 billion years

Using a sample of 98 galaxy clusters recently imaged in the near infra-red with the ESO NTT, WIYN and WHT telescopes, supplemented with 33 clusters from the ESO archive, we measure how the stellar mass of the most massive galaxies in the universe, namely Brightest Cluster Galaxies (BCG), increases with time. Most of the BCGs in this new sample lie in the redshift range $0.2<z<0.6$, which has been noted in recent works to mark an epoch over which the growth in the stellar mass of BCGs stalls. From this sample of 132 clusters, we create a subsample of 102 systems that includes only those clusters that have estimates of the cluster mass. We combine the BCGs in this subsample with BCGs from the literature, and find that the growth in stellar mass of BCGs from 10 billion years ago to the present epoch is broadly consistent with recent semi-analytic and semi-empirical models. As in other recent studies, tentative evidence indicates that the stellar mass growth rate of BCGs may be slowing in the past 3.5 billion years. Further work in collecting larger samples, and in better comparing observations with theory using mock images is required if a more detailed comparison between the models and the data is to be made.Comment: 15 pages, 8 tables, 7 figures - Accepted for publication in MNRA

A Prototype high resolution SiPM-based PET system for small volume imaging

Positron Emission Tomography (PET) is a molecular imaging technique which measures the distribution of positron-emitting radio-pharmaceuticals in a living subject by the detecting the γ-rays produced by positron-electron annihilations. Depending on the biological and chemical characteristics of the compound, many different functional processes within the living subject can be studied. Apart from the clinical applications of PET as a “routine imaging modality” in nuclear medicine, small-animal PET has become an important tool for preclinical studies, such as for the evaluation of new radiotracers and related therapies. The main requirements for small-animal PET are a uniform high spatial resolution, which is needed to resolve small structures in the reconstructed tracer distribution within the full field of view (FoV) and a high sensitivity, which allows the detection of small physiological changes and with the smallest levels of radiotracer uptake. The scintillator, detector, detector module, gantry, data acquisition systems and image analysis and reconstruction algorithms are all critical factors in the success of PET systems. In this Thesis, each of these aspects of system design are investigated, and an advanced low-cost small-animal PET system is designed and prototyped based on the results. The final imaging system, Compact Millimetre Resolution Positron Emission Tomography (CMRPET) is a high spatial resolution positron emission tomography (PET) scanner with full depth of interaction capability. Its pixellated scintillator and detector architecture allows the depth of interaction (DoI) of each 511 keV gamma ray event to be localised to a 3 x 3 x 3 mm3 scintillator voxel. The detector module configuration houses an edgeon 4 x 4 array of voxels, which ensures the high gamma ray detection sensitivity is not compromised. The incorporation of DoI in the design results in minimal degradation of spatial resolution in the reconstructed PET image across the field of view (FoV) of the scanner. The average spatial resolution measured is 2.0 mm with a standard deviation of 0.3 mm, measured using a 1 mm diameter source placed at different radial displacements inside the FoV. The prototype was validated by comparing simulation results with experimental results

Radioactive beams for ion therapy: Monte Carlo simulations and experimental verifications

Cancer is a leading cause of death worldwide with over 19 million new cases and 10 million deaths expected in 2020 [Hyuna et al. 22]. The precision of heavy ion therapy makes it particularly useful for treating deeply situated tumors while minimising damage to adjacent healthy tissue. However, due to the steep dose gradients, any deviation between the treatment plan and the delivered dose distribution can result in significant adverse effects on normal tissue, particularly if the treatment region is in the proximity of an organ at risk (OAR). Accurate and, ideally, real-time measurement of spatial dose distribution during irradiation would provide a mechanism for closed-loop control over the treatment process, minimising errors between the treatment plan and the actual delivered dose

Opportunistic dose amplification for proton and carbon ion therapy via capture of internally generated thermal neutrons

Abstract This paper presents Neutron Capture Enhanced Particle Therapy (NCEPT), a method for enhancing the radiation dose delivered to a tumour relative to surrounding healthy tissues during proton and carbon ion therapy by capturing thermal neutrons produced inside the treatment volume during irradiation. NCEPT utilises extant and in-development boron-10 and gadolinium-157-based drugs from the related field of neutron capture therapy. Using Monte Carlo simulations, we demonstrate that a typical proton or carbon ion therapy treatment plan generates an approximately uniform thermal neutron field within the target volume, centred around the beam path. The tissue concentrations of neutron capture agents required to obtain an arbitrary 10% increase in biological effective dose are estimated for realistic treatment plans, and compared to concentrations previously reported in the literature. We conclude that the proposed method is theoretically feasible, and can provide a worthwhile improvement in the dose delivered to the tumour relative to healthy tissue with readily achievable concentrations of neutron capture enhancement drugs

Performance comparison of two compact multiplexed readouts with SensL\u27s SPMArray4 for high-resolution detector module

The purpose of this study was to investigate a compact readout for silicon photomultiplier (SiPM) array in the development of high-resolution imaging detector to reduce the readout channels while maximizing the detectors performance. The detector module was composed of a LYSO scintillation crystal array and a SensL\u27s SPMArray4. The crystal array was coupled to the SiPM array with a 2mm-thick silicone pad to improve the light sharing among the SiPM array elements. Three LYSO crystal arrays of 4x4, 8x8 and 12x12 crystal elements with pixel sizes of 3.2, 1.6 and 1.0 mm were investigated in this study. Two compact multiplexed readouts based on the light sharing principle have been developed to reduce the detectors readout channels from 16 to 4 outputs while achieving a maximized performance in its spatial resolution. One is based on a conventional charge division method which was utilized with a discretized positioning circuit (DPC). The other is based on a novel two-stage charge division which was utilized with a symmetric charge division circuit to divide the charges from 16 SiPM elements into a 4-row and 4-column resistive network and then used a subtractive readout circuit to further reduce the readout channels from 8 to 4 outputs. The performance of the detector module with two compact multiplexed readouts was evaluated with LYSO arrays with different crystal sizes using a 137Cs point source. The preliminary results show that both compact multiplexed readouts can provide very good spatial resolution with good uniformity and resolve up to 1mm pixel elements of LYSO arrays. The compact readout based on the two-stage charge division with subtractive resistive-readout shows a slightly better improvement in the crystal identification while reducing the non-linearity of the flood image as compared to the DPC readout. In conclusion, both compact multiplexed readouts are effective approaches for the development of high-resolution detector module for compact micro-PET

Computational design and evaluation of a quad-MOSFET device for quality control of therapeutic accelerator-based neutron beams

Accurate real-time monitoring of neutron beams and distinguishing between thermal, epithermal and fast neutron components in the presence of a photon background is crucial for the effectiveness of accelerator-based boron neutron capture therapy (AB-BNCT). In this work, we propose an innovative quadruple metal–oxide–semiconductor field-effect transistor (MOSFET) device for real-time, cost-effective beam quality control; one detector is kept uncovered while the other three are covered with either a B4C, cadmium and B4C or polyethylene converter. Individual MOSFET converter configurations were optimised via Monte Carlo simulations to maximise signal selectivity across neutron energy spectra. Results demonstrate the quad-MOSFET device\u27s efficacy in quantifying changes in neutron flux, underscoring its potential as a useful instrument in the AB-BNCT quality control process

BeNEdiCTE (Boron NEutron CapTurE): a Versatile Gamma-Ray Detection Module for Boron Neutron Capture Therapy

We present a gamma-ray detection module for quantifying the boron neutron capture events that occur in Boron Neutron Capture Therapy (BNCT) and Neutron Capture Enhanced Particle Therapy (NCEPT). The goal of the module is to differentiate between the background prompt gamma peaks and the 478 keV neutron capture photopeak, in order to estimate the dose delivered to the patient. It is a compact module, coupling a large array of 64 SiPMs with a 2"×2" cylindrical LaBr3(Ce+Sr) scintillator crystal (73 ph/keV light yield, 25 ns decay time). The electronic front-end ASIC features low-noise processing of photodetector signals, while SiPMs pixellation and individual readout allow for position sensitivity in the crystal, although position estimation is not the object of this work. The module experimental characterization shows excellent energy resolution (2.7% FWHM at 662 keV), that allows to discriminate the neutron capture photons at 478 keV from the annihilation photons at 511 keV. The module features also an anti-coincidence circuit that provides a mechanism to distinguish and reject scintillation events created within specific temporal windows, thus enhancing the signal-to-background ratio of the spectrometer