Diode Detector Research Articles

Experimental Validation of Small-field Dosimetry in Radiotherapy Using Ionization Chamber and Edge Detector

Introduction: The radiotherapy treatment aims to deliver the maximum dose to the cancerous cells while preserving the healthy tissue. Recently, modern radiotherapy techniques have been extensively developed to deliver doses just to the therapeutic volume. Therefore, the exposure of smaller therapeutic fields is necessary. Because of the importance of dosimetry techniques in such field sizes, the objective of this work is to empirically evaluate the performance capability of an ionization chamber in comparison with edge detector.Materials and Methods: At first, the performance of ionization chamber compared with edge diode detector was validated at 10×10cm2 field size. Then, the percentage depth dose (PDD), the percentage surface dose and the transverse profile doses at the 2×2cm2, 3×3cm2 and 4×4cm2 field sizes were evaluated for both dosimeters. The empirical and statistical results in a water phantom were compared with those of the edge diode detector as the reference field dosimeter using Elekta 6MV linear accelerator. Results: The empirical and statistical results of transverse profiles of the ionization chamber and the edge detector are in a good agreement for the reference field of 10×10cm2. However, a small difference between the two dosimeters could be observed in small-fields. A discrepancy of less than 1% was observed between the results of PDDs for two dosimeters in small-fields.Conclusion: Dosimetric characteristics of ioization chamber and the edge detector illustrated some differences especially in terms of transverse profiles at small-field size. This discrepancy could be related to the volume effect of the chamber which influences on the penumbra. Because of the importance of sensitive organs, utilization of a special dosimeter for the small radiotherapy fields is recommended.

Envelope detection of a spinning linear radiation pattern based on diode detector algorithm for amplitude modulation

Envelope detection of a spinning linear radiation pattern based on diode detector algorithm for amplitude modulation

Preliminary Protocol Development of a HPLC-TBARS-EVSC (Ex Vivo Stratum Corneum) Assay for Skin Research: Application in a Sunscreen System

Considering the importance of the cutaneous tissue investigation and the need for the development of new protocols to non-invasively establish the safety and efficacy of dermocosmetics and topical products, we aimed at developing an HPLC-TBARS-EVSC (high performance liquid chromatography–thiobarbituric acid reactive species–ex vivo stratum corneum) assay for the lipid peroxidation measurement on subjects’ stratum corneum (SC) obtained by tape stripping; additionally, we applied the HPLC-TBARS-EVSC assay in an emulsified sunscreen system containing ethylhexyl triazone and bemotrizinol as UV filters. HPLC analysis was performed in isocratic mode with 35% methanol/65% phosphate buffer (pH 7.0) as the mobile phase. The diode detector was set at 532 nm to quantify the malondialdehyde (MDA)-TBA adduct. An ex vivo tape stripping method was applied in 10 volunteers in three pre-defined regions of the volar forearms: the control; the irradiated; and the site containing the sunscreen (2.0 mg·cm−2). Ten adhesive tapes per region were used for SC removal. An exclusive ex vivo protocol to measure SC lipid peroxidation was preliminarily developed with linearity and selectivity. The protocol suggested the use of an artificial irradiation dose (5506 KJ·m−2) to improve the assay response from the SC. The sunscreen system had a significative decrease in SC lipoperoxidative damage compared to the control. Our protocol can aid in the efficacy establishment of anti-UV and antioxidant agents, for instance, in studies that aim at elucidating the level of SC lipid peroxidation and even in carrying out baseline investigations characterizing different ethnicities and genders.

Dosimetric characterization of a new two-dimensional diode detector array used for stereotactic radiosurgery quality assurance

Dosimetric characterization of a new two-dimensional diode detector array used for stereotactic radiosurgery quality assurance

Dosimetric characterization of a new two-dimensional diode detector array used for stereotactic radiosurgery quality assurance

Dosimetric characterization of a new two-dimensional diode detector array used for stereotactic radiosurgery quality assurance

Characterization of the ZAP-X® Peripheral Dose Fall-Off.

Various small-field radiation dose detectors were systematically compared and their impact on measured beam performance of the ZAP-X® dedicated stereotactic radiosurgery system (ZAP Surgical Systems, Inc., San Carlos, CA, USA) was determined. Three Physikalische Technische Werkstaetten (PTW) diodes, i.e., the microSilicon, the microDiamond, and the Stereotactic Radiosurgery (SRS) diode detectors of (PTW-Freiburg, Freiburg, Germany), as well as Gafchromic™ External Beam Therapy 3 (EBT) film (Ashland, Inc., Wilmington, DE, USA), were used and compared to arrive at a recommended standard for this critical component of small-field beam measurements. Beam profiles, including the dose fall-off region near the edge of the beam, were measured with the PTW diodes and EBT3 film and subsequently contrasted. The impact of detector physical and dosimetric characteristics on the results of the measurements was investigated and compared with film measurements. The beam penumbra was used to quantify the dose fall-off. The measurement acquired with the diodes and film showed the most significant differences in the fall-off region near the field edge. The film-based measurements clearly showed the steepest dose gradient verified by the penumbra value of 1.21 mm, followed by the SRS diode with 1.60 mm, the microSilicon diode with 1.67 mm, and the microDiamond diode with 1.83 mm. A clear correlation of each detector’s sensitive area with the penumbra was found, with the microDiamond detector at 2.2 mm diameter sensitive area having the largest penumbra, followed by the microSilicon and SRS diodes. Beam measurements for the purposes of system characterization or treatment planning system beam data acquisition depend, to a large extent, on detector characteristics. This is especially true for small-field dosimetry performed during stereotactic radiosurgery beam measurements. Careful consideration should be practiced which allows for the measurements to represent true beam characteristics and minimize the impact of the detector on the measurements. We conclude that film should be considered the reference method for such measurements with the ZAP-X due to its smallest physical measurement resolution of 23.1 µm. Potential drawbacks to this methodology are the need to calibrate the film relative to the dose and possible problems with saturation and non-linear film response for very high and very low optical densities.

Validation of a secondary dose check tool against Monte Carlo and analytical clinical dose calculation algorithms in VMAT.

PurposePatient‐specific quality assurance (QA) is very important in radiotherapy, especially for patients with highly conformed treatment plans like VMAT plans. Traditional QA protocols for these plans are time‐consuming reducing considerably the time available for patient treatments. In this work, a new MC‐based secondary dose check software (SciMoCa) is evaluated and benchmarked against well‐established TPS (Monaco and Pinnacle3) by means of treatment plans and dose measurements.MethodsFifty VMAT plans have been computed using same calculation parameters with SciMoCa and the two primary TPSs. Plans were validated with measurements performed with a 3D diode detector (ArcCHECK) by translating patient plans to phantom geometry. Calculation accuracy was assessed by measuring point dose differences and gamma passing rates (GPR) from a 3D gamma analysis with 3%–2 mm criteria. Comparison between SciMoCa and primary TPS calculations was made using the same estimators and using both patient and phantom geometry plans.ResultsTPS and SciMoCa calculations were found to be in very good agreement with validation measurements with average point dose differences of 0.7 ± 1.7% and −0.2 ± 1.6% for SciMoCa and two TPSs, respectively. Comparison between SciMoCa calculations and the two primary TPS plans did not show any statistically significant difference with average point dose differences compatible with zero within error for both patient and phantom geometry plans and GPR (98.0 ± 3.0% and 99.0 ± 3.0% respectively) well in excess of the typical 95%clinical tolerance threshold.ConclusionThis work presents results obtained with a significantly larger sample than other similar analyses and, to the authors' knowledge, compares SciMoCa with a MC‐based TPS for the first time. Results show that a MC‐based secondary patient‐specific QA is a clinically viable, reliable, and promising technique, that potentially allows significant time saving that can be used for patient treatment and a per‐plan basis QA that effectively complements traditional commissioning and calibration protocols.

Building a VME spectrometer and testing Si PIN diode detector: a feasibility study for the first nuclear astrophysical experiments using a pelletron

This work presents the logical design, connections between NIM and VME elec­tronic modules, and the data acquisition programming to build a complete detector readout system. The test experiments were carried out with commercial silicon PIN diode S3590-09 bare detectors bombarded by charged particles from a 241Am α-source and Rutherford elastic backscattering (RBS) protons induced by 2.5 MeV proton beam bombarding on an Au-on-glass target, and with a NaI scintillation detector bombarded by gammas from 27Al(p, γ)28Si reaction with proton beam energy of 1.379 MeV. The test showed that the spectrometer operated steadily and its versatility for different kind of detector. The energy resolutions of the Si diodes were less than 0.5% energy of a charged particle, which satisfies the foreseen requirement for the upcoming experiments.

Technical Note: Characteristics of a microSilicon X shielded diode detector for photon beam dosimetry.

This study investigated the characteristics of a new shielded diode detector, microSilicon X (model 60022: MSX), for small-field and large-field dosimetry. The percent depth dose (PDD), beam profiles, detector output factor (OFdet ), temperature dependence, dose rate dependence, dose-per-pulse (DPP) dependence, and dose-response linearity of MSX were evaluated in Cyberknife and TrueBeam photon beams and compared with various detectors including microDiamond (PTW model 60019: MD), Sun Nuclear EDGE detector, Photon diode (PTW model 60016: PD), and semiflex ionization chamber (PTW model 31010: IC). For field sizes ranging from 50×50mm2 to 400×400mm2 , MSX-measured OFdet values were within 1% of the IC-measured values. For the CyberKnife small fields, the maximum difference between the MSX-measured OFdet and the MD-measured field output factor (Ω) was 4.0%, while the maximum differences were 8.8% and 10.9% for PD and EDGE, respectively. MSX showed a stable response within 0.7% for water temperatures of 5°C to 34°C, while PD and EDGE showed a linear correlation between the water temperature and the response. MSX showed small variations within 0.2% for the dose rate, and PD and EDGE showed logarithmic increases in the response with the dose rate. MSX and MD had smaller DPP dependences than PD and EDGE. The characteristics of MSX for measurements of small- and large-field photon beams are favorable. Compared to PD, MSX exhibited significant improvement in the over-response for small fields. The OFdet values measured by MSX were approximately in-between those measured by MD and PD. MSX showed stable responses against water temperature, dose rate, and DPP variations and provided suitable data for a wide range of field sizes. However, careful attention is required for measurements of OFdet for field sizes of <10×10mm2 and PDD for field sizes of ≥200×200mm2 .

Towards combined quantum bit detection and spatial tracking using an arrayed single-photon sensor.

Experimental quantum key distribution through free-space channels requires accurate pointing-and-tracking to co-align telescopes for efficient transmission. The hardware requirements for the sender and receiver could be drastically reduced by combining the detection of quantum bits and spatial tracking signal using two-dimensional single-photon detector arrays. Here, we apply a two-dimensional CMOS single-photon avalanche diode detector array to measure and monitor the single-photon level interference of a free-space time-bin receiver interferometer while simultaneously tracking the spatial position of the single-photon level signal. We verify an angular field-of-view of 1.28° and demonstrate a post-processing technique to reduce background noise. The experimental results show a promising future for two-dimensional single-photon detectors in low-light level free-space communications, such as quantum communications.

A novel contactless technique to measure water waves using a single photon avalanche diode detector array.

Commonly deployed measurement systems for water waves are intrusive and measure a limited number of parameters. This results in difficulties in inferring detailed sea state information while additionally subjecting the system to environmental loading. Optical techniques offer a non-intrusive alternative, yet documented systems suffer a range of problems related to usability and performance. Here, we present experimental data obtained from a 256 × 256 Single Photon Avalanche Diode (SPAD) detector array used to measure water waves in a laboratory facility. 12 regular wave conditions are used to assess performance. Picosecond resolution time-of-flight measurements are obtained, without the use of dye, over an area of the water surface and processed to provide surface elevation data. The SPAD detector array is installed 0.487 m above the water surface and synchronized with a pulsed laser source with a wavelength of 532 nm and mean power <1 mW. Through analysis of the experimental results, and with the aid of an optical model, we demonstrate good performance up to a limiting steepness value, ka, of 0.11. Through this preliminary proof-of-concept study, we highlight the capability for SPAD-based systems to measure water waves within a given field-of-view simultaneously, while raising potential solutions for improving performance.

A microwave detector based on spoof surface plasmon polaritons structure

In this paper, a Schottky diode detector based on spoof surface plasmon polariton (SPP) structure is reported. The detector consists of an input matching network, a Schottky diode, and an output filtering network. The proposed detector is designed using a step impedance section and λ/4 radial stub integrated in the circuit. Compared with the conventional microwave detector, experimental results show that the proposed detector achieves 31% improvement of detection sensitivity with the high input radio frequency (RF) power and 95% improvement of the detection sensitivity with the low input RF power by the SPPs. The proposed detector is attractive for use in aircraft, vehicles, and wireless communication due to its miniaturization, low-cost, and easy fabrication with planar circuits.

Single-photon avalanche diode detectors based on group IV materials

Today there are several types of photodetectors that can cope with the task of detecting a single photon, however, avalanche photodiodes are most widely used for applications in fiber-optic communication systems and quantum cryptography. In the past 5 years experimental fabrication of single-photon avalanche detectors within conventional complementary metal–oxide–semiconductor technology and by the method of molecular beam epitaxy have made possible many demonstrations of avalanche photodetectors with exceptional performance characteristics and opened wide perspectives for development of devices of new generation. In this work, we review state-of-the-art designs of single-photon avalanche photodiodes based on group IV materials, their operating characteristics, and achieved values of basic parameters, as well as the methods of their synthesis, and outline the perspectives of using such structures in emerging device applications.

A Method for Fast Acquisition of Photon Counts for SPAD LiDAR

The performance of LiDAR with single-photon avalanche diode (SPAD) detectors can degrade seriously when a shortage of photons occurs in adverse environments. It is desirable for SPAD LiDAR to accumulate enough photons so that reliable target detection is maintained under such conditions. It is proposed in this letter to adopt random laser-emitting schemes, such as stochastic pulse position modulation (SPPM), to have more laser pulses illuminated on targets to increase reflected photons. Accordingly, at the receiver side, a novel method, namely multi-start-multi-stop (MSMS), is proposed to work with SPPM to generate histograms for further processing of target detection and ranging. Theoretical analysis and experiments show that the SPPM+MSMS LiDAR can produce, with far less integration time, signal levels comparable to that of conventional LiDAR.

Chiral Separation of Diastereomeric and Enantiomeric Products Obtained by an Organic Reaction in Aqueous Media between Cyclohexanone and p‐nitrobenzaldehyde by HPLC on Chiral Stationary Phase

AbstractTo understand the intimate essence of the phenomena that occur around us and in us, it is necessary to go down to the atomic and molecular level. From the scale of atoms to the human one, nature is chiral (the term derives from the Greek χείρ, “hand,” that are not superimposable). A chiral chemical compound exists as two isomeric forms, called enantiomers, which are the mirror image of each other and cannot be superimposed on each other. It is important to understand the cause‐effect correlations of this asymmetry, which seems to be universal feature of many natural substances; in fact, many drugs, food additives, flavors, cosmetics, agrochemicals, and so on show chirality and surprisingly the biological activity of the two enantiomers is often different (for example one is biologically active, while the other is not active). To separate enanatiomers, an interaction with an entity that is also chiral with the formation of special interactions is required. This work describes the development of the separation method of four diastereoisomers obtained as products (adducts) of an organic reaction between cyclohexanone and benzaldehyde variously substituted in aromatic ring. The chiral separation of the two geometric isomers syn and anti adducts produced by the reaction is obtained by high performance chromatography with a diode detector (HPLC‐DAD), using a chiral column and a ternary mixture composed of n‐hexane, dichloromethane and ethanol.

Development of 10 MHz-1000MHz small leadless electric field probe.

In order to realize the miniaturization and leadless function of the electric field probe working from 10MHz to 1000MHz, a small stand-alone probe based on the dipole and Schottky detector diode is developed in this paper. First, a 20mm dipole printed on the circuit board is adopted as the receiving antenna, and the Schottky detector diode is connected across the two arms of the dipole. Then, the signal output by the detector diode is amplified by a chopper amplifier circuit, which also isolates the alternating component. Finally, a microprogrammed control unit is set inside the metal shield to realize data acquisition and storage. The size of the probe developed is not exceeding 20 × 20 × 30mm3, and the characteristics of the probe are temperature dependent. The field strength from 1.4 V/m to 1627 V/m can be measured within 10 MHz-1000MHz, achieving a dynamic range over 61 dB at 21 °C. It has the advantages of small size, large dynamic range, and integrated data collection and storage.

Commentary: "Indovation" in retinopathy of prematurity management during COVID-19 times.

The coronavirus disease-2019 (COVID-19) pandemic has caught many of us off-guard and thrust even the most developed of nations into chaos. While the direct implications of the disease have been much talked about, the collateral damage on patients suffering from non-COVID conditions has been equally severe. Retinopathy of prematurity (ROP) is an ocular emergency and any delay in treatment leads to permanent visual loss in a premature child. However, during the COVID-19 pandemic, lesser number of ROP babies got screened with an increasing proportion of them presenting with advanced disease.[1] Despite effective methods of treatment with laser and surgery, many premature neonates lost vision in the initial days of the COVID-19 lockdown due to late presentation.[23] To add to this, the fear of COVID-19 transmission led various doctors to reduce working hours, taking ROP care further away from those in need of it. In these testing times, Nayak et al.[4] have come out with a unique 'indovation' – The virus containment box. The basic concept stems from an incubator where ROP screening and laser are provided through the visualization provided by the slanting wall of the incubator.[5] The authors have described a low-cost setup that may be feasible at the level of a general ophthalmologist. While the authors must be applauded for their effort, a little note of caution is necessary here. Pros and Cons of Barrier Devices Barrier devices have become a commonplace due to the circumstances of the COVID-19 pandemic. Various designs of barrier devices for procedures such as mechanical intubation/resuscitation have been published over the past few months.[6789] Some devices even incorporate a negative pressure system to actively eliminate any aerosols that may be generated during the procedure. However, the impact of aerosols generated by a crying baby may not be completely gauged by the 'eye drop bottle' experiment applied by Nayak et al.[4] An airborne particle counter with a laser diode and photon detector to detect various sizes of airborne particles may be a better option. Simpson et al.[8] utilized the same to test various modifications of barrier devices during simulated intubation. A barrier device with suction to create negative pressure led to a reduction in 0.3, 0.5, 1.0, and 2.5 micron particles but not in the 5.0 micron particles when compared to no device used. On the contrary, a barrier device with no negative pressure actually showed an increase in 1.0, 2.5 and 5.0 micron particle count compared to no device use. The results for 0.3 micron particle size were similar whether any barrier device was used or not. A review of 52 publications describing various barrier devices by Sorbello et al.[9] also concluded that barrier devices may only be effective in limiting large droplet spread and not the aerosolised virus particles. While the aerosol containment barrier device may serve as an adjunct during the COVID-19 pandemic, the importance of adequate personal protective equipment and hand hygiene practices cannot be over stated. They remain our first line of defense in protecting ourselves from the pathogen while providing effective care. Pre-procedure testing before laser/surgery is another way of creating a safe workplace. It is during these procedures that a prolonged exposure is expected. Over the past 6 months, we have been testing all premature infants for COVID-19 by polymerase chain reaction who are to undergo laser/surgery for ROP. From over 100 babies tested, only one has tested positive so far. Thus the overall rate of positivity in neonates appears to be low and this has been substantiated by other studies as well.[10] Adequate availability of personal protective equipment, extensive COVID-19 testing, and an added layer of protection by barrier devices should encourage more and more ROP specialists to continue providing their services safely to prevent an impending pandemic of preventable childhood blindness.

Importance of Beam-Matching between TrueBeam STx and Novalis Tx in Pre-Treatment Quality Assurance Using Portal Dosimetry

Flexibility and efficiency in a radiotherapy department with different linear accelerators (linacs) can be improved if they are dosimetrically equivalent, and there is no need of plan or patient-specific quality assurance (PSQA) modification. From 2012 to 2017, our institution purchased three Novalis Tx and one TrueBeam STx beam-matched accelerators with the same high-resolution multileaf collimator (MLC). They are matched taking as reference dosimetric data from Novalis Tx SN-5479. We showed the importance of beam-matched dosimetric units by the use of electronic portal image device (EPID) and Delta4 PSQA. It was able to treat patients on a different machine than the machine used for PSQA. Depth dose, beam profiles, output factors, dosimetric leaf gap, and MLC transmission were compared for all energies and linacs. PSQA in all linacs for 30 volumetric-modulated arc therapy plans was also compared. Prostate, breast, and head-and-neck cases were selected to consider low, middle, and high plan complexity, respectively. The comparisons were evaluated using EPID and Delta4 phantom. Dosimetric differences between the three Novalis Tx and TrueBeam STx in all energies were lower than 1%. The only significant difference was observed in Novalis EPID in middle complexity when the criterion was tighter in distance. This result could be related with the nonsymmetric dose delivery of semi arcs. In all other cases, there were no differences in two different EPID evaluations. However, TrueBeam EPID values were slightly higher than Novalis EPID values. This could be associated with the high-resolution novel diode detector TrueBeam EPID. The dosimetric data indicated that the Novalis Tx and TrueBeam STx are equivalent. PSQA using EPID and Delta4 phantom showed that there are no dosimetric differences in any of the linacs. These results revealed the flexibility performance in PSQA by beam-matching.

SILICON CARBIDE NEUTRON DETECTOR PROTOTYPE TESTING AT THE JSI TRIGA REACTOR FOR ENHANCED BORDER AND PORTS SECURITY

In 2016, the “E-SiCure” project (standing for “Engineering Silicon Carbide for Border and Port Security”), funded by the NATO Science for Peace and Security Programme was launched. The main objective is to combine theoretical, experimental and applied research towards the development of radiation-hard SiC-based detectors of special nuclear materials (SNM), with the end goal to enhance border and port security barriers. Prototype neutron detectors, configured as 4H-SiC-based Schottky barrier diodes, were developed for the detection of secondary charged particles (tritons, alphas and lithium atoms) which are the result of thermal neutron reactions on 10B and 6LiF layers above the surface of the 4H-SiC diodes. We designed a stand-alone prototype detection system, consisting of a preamplifier, shaping amplifier and a multichannel analyser operated by a laptop computer, for testing of neutron detector prototypes at the Jožef Stefan Institute (JSI) TRIGA reactor using a broad beam of reactor neutrons. The reverse bias for the detector diode and the power to electronic system were provided by a standalone battery-powered voltage source. The detector functionality was established through measurements using an 241Am alpha particle source. Two dedicated experimental campaigns were performed at the JSI TRIGA reactor. The registered pulse height spectra from the detectors, using both 10B and 6LiF neutron converting layers, clearly demonstrated the neutron detection abilities of the SiC detector prototypes. The computed neutron detection sensitivity of the single prototype detectors demonstrates that scaling SiC detectors into larger arrays, of dimensions relevant for border and port radiation detectors, could enable neutron sensitivity levels matching gas-based detector technology.

The possibility of using tantalum oxide microparticles in phosphate glass for radiation therapy of malignant neoplasms

Objective: The creation of the medicine for a local radiomodification of tumors.Methods: The level of the secondary radiation on the surface of the phosphate glass powder with the inclusion of tantalum oxide processed by 6 MeV deceleration emission was studied. Medical linear accelerator TrueBeam (Varian, USA), and Semiconductor diode detector PDI 2.0 (Sun Nuclear Corp., USA) having the system of moving in vertical plane and the system of position video recording were used.Results: The presence of the phosphate glass (containing 20% Та2О5) on the surface gave a 63.7% increase to the secondary radiation. It’s around two thirds of the overall level.Conclusion: An opportunity to create a medicine on the basis of phosphate glass, containing tantalum oxide, for local radiomodification of malignant tumors.