BrachyView: initial preclinical results for a real-time in-body HDR PBT source tracking system with simultaneous TRUS image fusion.

A prototype in-body gamma camera system with integrated trans-rectal ultrasound (TRUS) and associated real-time image acquisition and analysis software was developed for intraoperative source tracking in high dose rate (HDR) brachytherapy. The accuracy and temporal resolution of the system was validated experimentally using a deformable tissue-equivalent prostate gel phantom and a full clinical HDR treatment plan. The BrachyView system was able to measure 78% of the 200 source positions with an accuracy of better than 1 mm. A minimum acquisition time of 0.28 s/frame was required to achieve this accuracy, restricting dwell times to a minimum of 0.3 s. Additionally, the performance of the BrachyView-TRUS fusion probe for mapping the spatial location of the tracked source within the prostate volume was evaluated. A global coordinate system was defined by scanning the phantom with the probe in situ using a CT scanner, and was subsequently used for co-registration of the BrachyView and TRUS fields of view (FoVs). TRUS imaging was used to segment the prostate volume and reconstruct it into a three-dimensional (3D) image. Fusion of the estimated source locations with the 3D prostate image was performed using integrated 3D visualisation software. HDR BrachyView is demonstrated to be a valuable tool for intraoperative source tracking in HDR brachytherapy, capable of resolving source dwell locations relative to the prostate anatomy when combined with TRUS.

Dose reconstruction from PET images in carbon ion therapy: a deconvolution approach.

Dose and range verification have become important tools to bring carbon ion therapy to a higher level of confidence in clinical applications. Positron emission tomography is among the most commonly used approaches for this purpose and relies on the creation of positron emitting nuclei in nuclear interactions of the primary ions with tissue. Predictions of these positron emitter distributions are usually obtained from time-consuming Monte Carlo simulations or measurements from previous treatment fractions, and their comparison to the current, measured image allows for treatment verification. Still, a direct comparison of planned and delivered dose would be highly desirable, since the dose is the quantity of interest in radiation therapy and its confirmation improves quality assurance in carbon ion therapy. In this work, we present a deconvolution approach to predict dose distributions from PET images in carbon ion therapy. Under the assumption that the one-dimensional PET distribution is described by a convolution of the depth dose distribution and a filter kernel, an evolutionary algorithm is introduced to perform the reverse step and predict the depth dose distribution from a measured PET distribution. Filter kernels are obtained from either a library or are created for any given situation on-the-fly, using predictions of the [Formula: see text]-decay and depth dose distributions, and the very same evolutionary algorithm. The applicability of this approach is demonstrated for monoenergetic and polyenergetic carbon ion irradiation of homogeneous and heterogeneous solid phantoms as well as a patient computed tomography image, using Monte Carlo simulated distributions and measured in-beam PET data. Carbon ion ranges are predicted within less than 0.5 mm and 1 mm deviation for simulated and measured distributions, respectively.

BrachyView: Combining LDR seed positions with transrectal ultrasound imaging in a prostate gel phantom.

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 2.5mm slice thickness. Eleven needles containing a total of thirty 0.508U125I 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 1.78mm, with 75% of the seeds reconstructed within 1mm 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.

BrachyView, a novel in-body imaging system for HDR prostate brachytherapy: Experimental evaluation.

PURPOSE: This paper presents initial experimental results from a prototype of high dose rate (HDR) BrachyView, a novel in-body source tracking system for HDR brachytherapy based on a multipinhole tungsten collimator and a high resolution pixellated silicon detector array. The probe and its associated position estimation algorithms are validated and a comprehensive evaluation of the accuracy of its position estimation capabilities is presented. METHODS: The HDR brachytherapy source is moved through a sequence of positions in a prostate phantom, for various displacements in x, y, and z. For each position, multiple image acquisitions are performed, and source positions are reconstructed. Error estimates in each dimension are calculated at each source position and combined to calculate overall positioning errors. Gafchromic film is used to validate the accuracy of source placement within the phantom. RESULTS: More than 90% of evaluated source positions were estimated with an error of less than one millimeter, with the worst-case error being 1.3 mm. Experimental results were in close agreement with previously published Monte Carlo simulation results. CONCLUSIONS: The prototype of HDR BrachyView demonstrates a satisfactory level of accuracy in its source position estimation, and additional improvements are achievable with further refinement of HDR BrachyView's image processing algorithms.

A new virtual ring-based system matrix generator for iterative image reconstruction in high resolution small volume PET systems.

A common approach to improving the spatial resolution of small animal PET scanners is to reduce the size of scintillation crystals and/or employ high resolution pixellated semiconductor detectors. The large number of detector elements results in the system matrix--an essential part of statistical iterative reconstruction algorithms--becoming impractically large. In this paper, we propose a methodology for system matrix modelling which utilises a virtual single-layer detector ring to greatly reduce the size of the system matrix without sacrificing precision. Two methods for populating the system matrix are compared; the first utilises a geometrically-derived system matrix based on Siddon's ray tracer method with the addition of an accurate detector response function, while the second uses Monte Carlo simulation to populate the system matrix. The effectiveness of both variations of the proposed technique is demonstrated via simulations of PETiPIX, an ultra high spatial resolution small animal PET scanner featuring high-resolution DoI capabilities, which has previously been simulated and characterised using classical image reconstruction methods. Compression factors of 5 x 10(7) and 2.5 x 10(7)are achieved using this methodology for the system matrices produced using the geometric and Monte Carlo-based approaches, respectively, requiring a total of 0.5-1.2 GB of memory-resident storage. Images reconstructed from Monte Carlo simulations of various point source and phantom models, produced using system matrices generated via both geometric and simulation methods, are used to evaluate the quality of the resulting system matrix in terms of achievable spatial resolution and the CRC, CoV and CW-SSIM index image quality metrics. The Monte Carlo-based system matrix is shown to provide the best image quality at the cost of substantial one-off computational effort and a lower (but still practical) compression factor. Finally, a straightforward extension of the virtual ring method to a three dimensional virtual cylinder is demonstrated using a 3D DoI PET scanner.

Radiation dose enhancement at tissue-tungsten interfaces in HDR brachytherapy.

HDR BrachyView is a novel in-body dosimetric imaging system for real-time monitoring and verification of the source position in high dose rate (HDR) prostate brachytherapy treatment. It is based on a high-resolution pixelated detector array with a semi-cylindrical multi-pinhole tungsten collimator and is designed to fit inside a compact rectal probe, and is able to resolve the 3D position of the source with a maximum error of 1.5 mm. This paper presents an evaluation of the additional dose that will be delivered to the patient as a result of backscatter radiation from the collimator. Monte Carlo simulations of planar and cylindrical collimators embedded in a tissue-equivalent phantom were performed using Geant4, with an (192)Ir source placed at two different source-collimator distances. The planar configuration was replicated experimentally to validate the simulations, with a MOSkin dosimetry probe used to measure dose at three distances from the collimator. For the cylindrical collimator simulation, backscatter dose enhancement was calculated as a function of axial and azimuthal displacement, and dose distribution maps were generated at three distances from the collimator surface. Although significant backscatter dose enhancement was observed for both geometries immediately adjacent to the collimator, simulations and experiments indicate that backscatter dose is negligible at distances beyond 1 mm from the collimator. Since HDR BrachyView is enclosed within a 1 mm thick tissue-equivalent plastic shell, all backscatter radiation resulting from its use will therefore be absorbed before reaching the rectal wall or other tissues. dosimetry, brachytherapy, HDR.

BrachyView, a novel inbody imaging system for HDR prostate brachytherapy: design and Monte Carlo feasibility study.

PURPOSE: High dose rate (HDR) brachytherapy is a form of radiation therapy for treating prostate cancer whereby a high activity radiation source is moved between predefined positions inside applicators inserted within the treatment volume. Accurate positioning of the source is essential in delivering the desired dose to the target area while avoiding radiation injury to the surrounding tissue. In this paper, HDR BrachyView, a novel inbody dosimetric imaging system for real time monitoring and verification of the radioactive seed position in HDR prostate brachytherapy treatment is introduced. The current prototype consists of a 15 × 60 mm(2) silicon pixel detector with a multipinhole tungsten collimator placed 6.5 mm above the detector. Seven identical pinholes allow full imaging coverage of the entire treatment volume. The combined pinhole and pixel sensor arrangement is geometrically designed to be able to resolve the three-dimensional location of the source. The probe may be rotated to keep the whole prostate within the transverse plane. The purpose of this paper is to demonstrate the efficacy of the design through computer simulation, and to estimate the accuracy in resolving the source position (in detector plane and in 3D space) as part of the feasibility study for the BrachyView project. METHODS: Monte Carlo simulations were performed using the GEANT4 radiation transport model, with a (192)Ir source placed in different locations within a prostate phantom. A geometrically accurate model of the detector and collimator were constructed. Simulations were conducted with a single pinhole to evaluate the pinhole design and the signal to background ratio obtained. Second, a pair of adjacent pinholes were simulated to evaluate the error in calculated source location. RESULTS: Simulation results show that accurate determination of the true source position is easily obtainable within the typical one second source dwell time. The maximum error in the estimated projection position was found to be 0.95 mm in the imaging (detector) plane, resulting in a maximum source positioning estimation error of 1.48 mm. CONCLUSIONS: HDR BrachyView is a feasible design for real-time source tracking in HDR prostate brachytherapy. It is capable of resolving the source position within a subsecond dwell time. In combination with anatomical information obtained from transrectal ultrasound imaging, HDR BrachyView adds a significant quality assurance capability to HDR brachytherapy treatment systems.

BrachyView: proof-of-principle of a novel in-body gamma camera for low dose-rate prostate brachytherapy.

PURPOSE: The conformity of the achieved dose distribution to the treatment plan strongly correlates with the accuracy of seed implantation in a prostate brachytherapy treatment procedure. Incorrect seed placement leads to both short and long term complications, including urethral and rectal toxicity. The authors present BrachyView, a novel concept of a fast intraoperative treatment planning system, to provide real-time seed placement information based on in-body gamma camera data. BrachyView combines the high spatial resolution of a pixellated silicon detector (Medipix2) with the volumetric information acquired by a transrectal ultrasound (TRUS). The two systems will be embedded in the same probe so as to provide anatomically correct seed positions for intraoperative planning and postimplant dosimetry. Dosimetric calculations are based on the TG-43 method using the real position of the seeds. The purpose of this paper is to demonstrate the feasibility of BrachyView using the Medipix2 pixel detector and a pinhole collimator to reconstruct the real-time 3D position of low dose-rate brachytherapy seeds in a phantom. METHODS: BrachyView incorporates three Medipix2 detectors coupled to a multipinhole collimator. Three-dimensionally triangulated seed positions from multiple planar images are used to determine the seed placement in a PMMA prostate phantom in real time. MATLAB codes were used to test the reconstruction method and to optimize the device geometry. RESULTS: The results presented in this paper show a 3D position reconstruction accuracy of the seed in the range of 0.5-3 mm for a 10-60 mm seed-to-detector distance interval (Z direction), respectively. The BrachyView system also demonstrates a spatial resolution of 0.25 mm in the XY plane for sources at 10 mm distance from Medipix2 detector plane, comparable to the theoretical value calculated for an equivalent gamma camera arrangement. The authors successfully demonstrated the capability of BrachyView for real-time imaging (using a 3 s data acquisition time) of different brachytherapy seed configurations (with an activity of 0.05 U) throughout a 60 × 60 × 60 mm(3) Perspex prostate phantom. CONCLUSIONS: The newly developed miniature gamma camera component of BrachyView, with its high spatial resolution and real time capability, allows accurate 3D localization of seeds in a prostate phantom. Combination of the gamma camera with TRUS in a single probe will complete the BrachyView system.