The magnetic field of a transverse MR-linac alters electron trajectories as the photon beam transits through materials, causing lower doses at flat entry surfaces and increased doses at flat ...beam-exiting surfaces. This study investigated the response of a MOSFET detector, known as the MO
Skin
™, for high-resolution surface and near-surface percentage depth dose measurements on an Elekta Unity. Simulations with Geant4 and the Monaco treatment planning system (TPS), and EBT-3 film measurements, were also performed for comparison. Measured MO
Skin
™ entry surface doses, relative to D
max
, were (9.9 ± 0.2)%, (10.1 ± 0.3)%, (11.3 ± 0.6)%, (12.9 ± 1.0)%, and (13.4 ± 1.0)% for 1 × 1 cm
2
, 3 × 3 cm
2
, 5 × 5 cm
2
, 10 × 10 cm
2
, and 22 × 22 cm
2
fields, respectively. For the investigated fields, the maximum percent differences of Geant4, TPS, and film doses extrapolated and interpolated to a depth suitable for skin dose assessment at the beam entry, relative to MO
Skin
™ measurements at an equivalent depth were 1.0%, 2.8%, and 14.3%, respectively, and at a WED of 199.67 mm at the beam exit, 3.2%, 3.7% and 5.7%, respectively. The largest measured increase in exit dose, due to the electron return effect, was 15.4% for the 10 × 10 cm
2
field size using the MO
Skin
™ and 17.9% for the 22 × 22 cm
2
field size, using Geant4 calculations. The results presented in the study validate the suitability of the MO
Skin
™ detector for transverse MR-linac surface dosimetry.
Purpose:
High dose rate (HDR) brachytherapy is a radiation treatment technique capable of delivering large dose rates to the tumor. Radiation is delivered using remote afterloaders to drive highly ...active sources (commonly192Ir with an air KERMA strength range between 20 000 and 40 000 U, where 1 U = 1 μGy m2/h in air) through applicators directly into the patient's prescribed region of treatment. Due to the obvious ramifications of incorrect treatment while using such an active source, it is essential that there are methods for quality assurance (QA) that can directly and accurately verify the treatment plan and the functionality of the remote afterloader. This paper describes the feasibility study of a QA system for HDR brachytherapy using a phantom based two-dimensional 11 × 11 epitaxial diode array, named “magic phantom.”
Methods:
The HDR brachytherapy treatment plan is translated to the phantom with two rows of 10 (20 in total) HDR source flexible catheters, arranged above and below the diode array “magic plate” (MP). Four-dimensional source tracking in each catheter is based upon a developed fast iterative algorithm, utilizing the response of the diodes in close proximity to the192Ir source, sampled at 100 ms intervals by a fast data acquisition (DAQ) system. Using a 192Ir source in a solid water phantom, the angular response of the developed epitaxial diodes utilized in the MP and also the variation of the MP response as a function of the source-to-detector distance (SDD) were investigated. These response data are then used by an iterative algorithm for source dwelling position determination. A measurement of the average transit speed between dwell positions was performed using the diodes and a fast DAQ.
Results:
The angular response of the epitaxial diode showed a variation of 15% within 360°, with two flat regions above and below the detector face with less than 5% variation. For SDD distances of between 5 and 30 mm the relative response of the epitaxial diodes used in the MP is in good agreement (within 8%) with radial dose function measurements found within the TG-43 protocol, with SDD of up to 70 mm showing a 40% over response. A method for four-dimensional localization of the HDR source was developed, allowing the source dwell position to be derived within 0.50 mm of the expected position. An estimation of the average transit speed for varying step sizes was determined and was found to increase from (12.8 ± 0.3) up to (38.6 ± 0.4) cm/s for a step size of 2.5 and 50 mm, respectively.
Conclusions:
Our characterization of the designed QA “magic phantom” with MP in realistic HDR photon fields demonstrates the promising performance for real-time source position tracking in four dimensions and measurements of transit times. Further development of this system will allow a full suite for QA in HDR brachytherapy and analysis, and for futurein vivo tracking.
Radiation monitoring in space radiation is complex due to galactic cosmic rays (GCRs), solar particle events (SPEs), and albedo particles. Thermal neutrons are an important component in the Moon ...radiation albedo field which can cause single event upset (SEU) in electronics when they interact with the 10 B present in electronic components. In this work, we studied an application of silicon on insulator (SOI) microdosimeters for neutron monitoring in various mixed radiation field environments. A 10-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> SOI microdosimeter was utilized in conjunction with a 10 B 4 C thin-film converter to successfully measure the thermal neutron contribution out of field of a therapeutic proton beam as well as an 18-MV X-ray linear accelerator (LINAC). The microdosimeter was placed downstream of the Bragg peak (BP) as well as laterally out of field of the proton beam and at two positions along the treatment couch of the 18-MV LINAC. It was demonstrated that the 10-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> SOI microdosimeter with 10 B 4 C converter is suitable for detection of thermal neutrons with excellent discrimination of gamma, fast and thermal neutron components in the presence of a gamma-neutron pulsed field of an 18-MV LINAC. To reduce the gamma contribution and further improve detection of neutrons in mixed radiation fields, a new <inline-formula> <tex-math notation="LaTeX">2 ~\mu \text{m} </tex-math></inline-formula> Mushroom-planar microdosimeter was fabricated and characterized in detail using an ion beam induced charge collection (IBIC) technique with 1.78 MeV <inline-formula> <tex-math notation="LaTeX">\text{H}e^{\mathrm {2+}} </tex-math></inline-formula> ions. It was demonstrated that this <inline-formula> <tex-math notation="LaTeX">2 ~\mu \text{m} </tex-math></inline-formula> SOI microdosimeter can be operated in a passive mode. The SOI microdosimeter with the 10 B 4 C converter can be recommended for the detection of thermal neutrons for SEU prediction in the mixed gamma-neutron fields during space missions, especially for the Moon mission.
BrachyView is a novel in-body imaging system developed to provide real-time intraoperative dosimetry for low dose rate prostate brachytherapy treatments. Seed positions can be reconstructed after ...in-vivo implantation using a high-resolution pinhole gamma camera inserted into the patient rectum. The obtained data is a set of 2D projections of the seeds on the image plane. The 3D reconstruction algorithm requires the identification of the seed's centre of mass. This work presents the development and techniques adopted to build an algorithm that provides the means for fully automatic seed centre of mass identification and 3D position reconstruction for real-time applications. The algorithm presented uses a local feature detector, speeded up robust features, to perform detection of brachytherapy seed 2D projections from images, allowing for robust seed identification. Initial results have been obtained with datasets of 30, 96 and 98 I-125 brachytherapy seeds implanted into a prostate gel phantom. It can detect 97% of seeds and correctly match 97% of seeds. The average overall computation time of 2.75 s per image and improved reconstruction accuracy of 22.87% for the 98 seed dataset was noted. Elimination processes for initial false positive detection removal have shown to be extremely effective, resulting in a 99.9% reduction of false positives, and when paired with automatic frame alignment and subtraction procedures allows for the effective removal of excess counts generated by previously implanted needles. The proposed algorithm will allow the BrachyView system to be used as a real-time intraoperative dosimetry tool for low dose rate prostate brachytherapy treatments.
First Observations of the New MEXART's Digital System Gonzalez‐Esparza, J. A.; Mejia‐Ambriz, J. C.; Aguilar‐Rodriguez, E. ...
Radio science,
January 2022, 2022-01-00, 20220101, Letnik:
57, Številka:
1
Journal Article
Recenzirano
The Mexican Array Radio Telescope (MEXART) is a transit instrument mainly dedicated to performing interplanetary scintillation (IPS) observations with a central operating frequency of 139.65 MHz. The ...main scientific objective is to perform studies of solar wind properties and space weather effects. MEXART initially operated with an analog beam former (16 × 16 Butler matrix), which produced 16 fixed latitudinal beams. MEXART began operations and reported the first measurements of IPS sources. MEXART's beam forming system had several problems, however. The North‐South beams had poor directivity, with large side lobes, and the instrument did not achieve the expected performance. Therefore, we commissioned the design and construction of a digital back‐end. The digital system solved the problems with the beam forming, increases the bandwidth, and significantly improves the instrument's sensitivity. In this paper, we present the first light of MEXART's digital system. We describe the new technical capabilities of the instrument, and we show some preliminary results: an estimation of the radio telescope's sensitivity (ΔSmin = 2.28 ± 0.23 Jy), the transit of the Galaxy at 140 MHz with the simultaneous tracking of 62 latitudinal beams, and an example of an IPS observation and the single‐station methodology for calculating the solar wind speed. The new technical capabilities of the radio telescope will provide the potential for participating in several scientific studies. These include solar wind properties, space weather forecasting, ionospheric perturbations, and astrophysical aims such as the monitoring of repeating fast radio bursts and pulsars' observations.
Key Points
Radio telescope dedicated to the study of solar wind properties and space weather effects using the interplanetary scintillation technique
The new digital backend has several beamforming configurations, increases the bandwidth, and improves the instrument's sensitivity
With the new technical capabilities, the instrument can participate in space weather forecasting and other astrophysical studies
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.
Purpose:
The MOSkin is a MOSFET detector designed especially for skin dose measurements. This detector has been characterized for various factors affecting its response for megavoltage photon beams ...and has been used for patient dose measurements during radiotherapy procedures. However, the characteristics of this detector in kilovoltage photon beams and low dose ranges have not been studied. The purpose of this study was to characterize the MOSkin detector to determine its suitability for in vivo entrance skin dose measurements during interventional radiology procedures.
Methods:
The calibration and reproducibility of the MOSkin detector and its dependency on different radiation beam qualities were carried out using RQR standard radiation qualities in free‐in‐air geometry. Studies of the other characterization parameters, such as the dose linearity and dependency on exposure angle, field size, frame rate, depth‐dose, and source‐to‐surface distance (SSD), were carried out using a solid water phantom under a clinical x‐ray unit.
Results:
The MOSkin detector showed good reproducibility (94%) and dose linearity (99%) for the dose range of 2 to 213 cGy. The sensitivity did not significantly change with the variation of SSD (±1%), field size (±1%), frame rate (±3%), or beam energy (±5%). The detector angular dependence was within ±5% over 360° and the dose recorded by the MOSkin detector in different depths of a solid water phantom was in good agreement with the Markus parallel plate ionization chamber to within ±3%.
Conclusions:
The MOSkin detector proved to be reliable when exposed to different field sizes, SSDs, depths in solid water, dose rates, frame rates, and radiation incident angles within a clinical x‐ray beam. The MOSkin detector with water equivalent depth equal to 0.07 mm is a suitable detector for in vivo skin dosimetry during interventional radiology procedures.
•The MOSkin dosimeter was characterized for X-ray diagnostic CT beams.•The system was tested in a metrology laboratory and in clinical conditions.•The MOSkin demonstrated potential for applications ...in CT dosimetry.
The aim of the present study was to evaluate the response of the MOSkin MOSFET dosimeter for X-ray diagnostic CT beams. Experiments were performed to investigate the sensitivity, energy dependence, reproducibility, fading and angular dependence of the dose response for the device. The dosimeter’s performance was evaluated for the standard radiation qualities RQT 8, RQT 9 and RQT 10 in a metrology laboratory. In a CT scanner, the MOSkin was used to assess the air kerma profile and the dose profile in a phantom. The integral of the dose profile was compared to the CPMMA,100 measured with a pencil ionization chamber. The results showed that the MOSkin response was linear and reproducible with doses in the CT range. Energy dependence varied up to a factor of 1.19 among the tested X-ray energies. Angular dependence of the response was not greater than 7.8% within the angle range from 0 to 90 degrees. Signal fading within 3 min was negligible. Additionally, the MOSkin was able to accurately assess the air kerma profile and the integral of the dose profile in a CT scanner. The integral of the dose profile in a phantom was in agreement with the CPMMA,100. The presented results demonstrated the potential of the MOSkin for application in CT dosimetry.
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 192Ir 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
Intraocular cancer is a serious threat to the lives of those that suffer from it. Dosimetry for eye brachytherapy presents a significant challenge due to the inherently steep dose gradients that are ...needed to treat such small tumours in close proximity to sensitive normal structures. This issue is addressed by providing much needed quality assurance to eye brachytherapy, a novel volumetric dosimetry system, called Panoptes was developed. This study focuses on the preliminary characterisation and calibration of the system. Using ion beam facilities, the custom, pixelated silicon detector of Panoptes was shown to have good charge collection uniformity and a well defined sensitive volume. Flat-field calibration was conducted on the device using a 250 kVp orthovoltage beam. Finally, the detector and phantom were simulated with Monte Carlo in Geant4, to create water equivalent dose correction factors for each pixel across a range of angles.
•Volumetric detector system produced for plaque brachytherapy.•Orthovoltage, flat-field calibration performed for detector pixels.•Monte Carlo simulation showed mostly little angular deviation across all angles.•Ion beam induced charge collection showed pixels uniform and fully depleted.
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