Solid-state Radiation Detectors Research Articles

Visible proton Bragg curve imaging by colour centre photoluminescence in radiation detectors based on lithium fluoride films on silica

Passive solid-state radiation detectors, based on the visible photoluminescence (PL) of radiation-induced colour centres in optically transparent lithium fluoride (LiF), polycrystalline thin films are under investigation for proton beam advanced diagnostics. After proton exposure, the latent images stored in LiF as local formations of stable F2 and F3 + aggregate defects, are directly read with a fluorescence microscope under illumination in the blue spectral range. Adopting a suitable irradiation geometry, the energy density that protons deposit in the material can be recorded as a spatial distribution of these light-emitting defects, from which a luminous replica of the proton Bragg curve can be thereafter extracted and analysed to reconstruct the proton beam energy spectrum. Their peculiar properties, such as wide dynamic range and linearity of the spectrally-integrated PL response vs. dose, make the investigation of two-dimensional LiF film radiation detectors grown on several types of substrate highly attractive. Here, the case of a LiF thin film thermally evaporated on a silica substrate, irradiated at grazing incidence with a 35 MeV proton beam, is investigated and reported for the first time. A comparison of the measured photoluminescent Bragg curve with Monte Carlo simulations demonstrates that the Bragg peak in the film is located at the very same position that would be expected in the underlying silica substrate rather than in LiF. The film packing density is shown not to have a significant effect on the peak depth, while even small nonzero grazing angle of the impinging proton beam is able to significantly modify the shape of the Bragg curve. These findings are ascribed to the effects of multiple Coulomb scattering in both the film and the substrate and are interesting for proton beam diagnostics and dosimetry.

Optimization of low-noise read-out electronics for high energy resolution X-ray strip detectors

Semiconductor strip sensors applied as solid-state radiation or particle detectors can be used in radiation detection and measurement for various applications in particle physics experiments, X-ray imaging (e.g. medical), or material science. The X-ray imaging devices with spectroscopic and position resolution features are a very important research topic at many institutes and companies worldwide. Short strip silicon detectors are good candidates for X-ray spectroscopy, because of their relatively small capacitance and leakage current. If additionally, strip pitch is below 100 μm, then the high spatial resolution is also possible. In this paper, the analysis and noise optimization of the read-out electronics for short silicon strip detectors with Charge Sensitive Amplifier (CSA) and shaping amplifier (shaper) is presented. The CSA is optimized for the detector capacitance of around 1.5 pF, and the shaper nominal peaking time is about 1 μs (controlled by the sets of switches). We take into account the sources of noise in a radiation imaging system (current parallel noise, voltage series noise, and 1/f or flicker series noise) both internal (related to the front-end electronics itself) but also external, stemming from a sensor, interconnect, or printed circuit board parasitic components. We target the noise level below 40 el. rms, considering low power consumption (a few mW) and limited channel area.

Addressing the Voltage Induced Instability Problem of Perovskite Semiconductor Detectors

Perovskite-based solid-state radiation detectors have delivered impressive performances, but the electrical field induced instability has been a major detriment for the further development. Here, we identify the voltage-induced instability is directly tied to the humidity levels. A higher humidity elicits a hysteresis in the current–voltage curve and lowers the breakdown voltage. We further add a fluorinated phenylethylamine iodide (5F-PEAI) barrier layer on the perovskite, which protects the device against voltage damage. Photoluminescence maps identify the ion migration and degradation can be suppressed by 5F-PEAI. Quantum chemical simulations corroborate experimental results by revealing high energy barrier for water penetrating the 5F-PEAI layer with enhancing stability of halide perovskite under humid condition. Using a treated device, we demonstrate high X-ray sensitivities approaching 1000 μC/(Gyair·cm2) under high biases. Our work provides a mechanistic understanding on the voltage instability of 2D perovskite detectors and provides a viable solution toward robust detector development.

Dose response and Bragg curve reconstruction by radiophotoluminescence of color centers in lithium fluoride crystals irradiated with 35 MeV proton beams from 0.5 to 50 Gy

Passive solid-state radiation detectors, based on the radiophotoluminescence of stable color centers in nominally pure lithium fluoride (LiF) crystals, have been used for advanced diagnostics of the segment up to 35 MeV of the TOP-IMPLART proton linear accelerator for protontherapy applications, under development at ENEA Frascati. In LiF, proton beams generate a spatial distribution of F2 and F3+ aggregate color centers, which efficiently emit radiophotoluminescence in the red-green spectral range under optical pumping around 450 nm. LiF crystals were irradiated with 35 MeV nominal energy protons at several doses of interest for protontherapy (from 0.5 to 50 Gy). For the first time is shown here the possibility of measuring the radiophotoluminescence spectra of proton irradiated LiF even at such low doses and how the signal showed a linear behavior with dose with a good signal-to-noise ratio. A Bragg-curve image, stored as color-center distribution in a LiF crystal after a 50 Gy-dose irradiation in a particular geometry, was acquired in a conventional fluorescence microscope. After appropriate image processing, the signal intensity resulted to be proportional to the linear energy transfer along the whole Bragg curve. By best-fitting it with an ad-hoc analytical formula, the depth-dose distribution was reconstructed and the proton beam energy and energy spread were estimated.

Determination of Nonmetallic Inclusions in Metal Alloys by the Method of Spark Atomic Emission Spectroscopy (Review)

The literature on the determination of nonmetallic inclusions in metal alloys by the method of atomic emission spectroscopy with single-spark spectra registration is reviewed. The main advantage of this method is its high rapidity (~1 min per measurement), which makes it useful for direct production control. When the spark discharge hits a nonmetallic inclusion, it leads to a high peak (outlier) in the intensity of spectral lines of the elements contained in the inclusion, since the content of these elements in the metal matrix is usually much lower. The intensity distribution of the spectral line of the element obtained from several thousand single-spark spectra consists of two parts: (i) the Gaussian function corresponding to the content of the element in the dissolved form, and (ii) an asymmetric residue in the region of high intensity values due to the inclusions. The quantitative determination of inclusions is based on the assumption that the intensity of the spectral line of an element in the single-spark spectrum is proportional to the content of this element in the mass of the substance ablated by the spark discharge. Thus, according to the calibration curve, which is obtained using the samples with the certified total content of the element, it is possible to determine not only the fractions of the dissolved and undissolved element but also the size of individual inclusions. However, the determination of the sizes is limited to a range of 1 to 20 μm. Furthermore, at present, only Al-containing inclusions can be quantitatively determined. Difficulties arise both with elements that are practically insoluble in steels (O, Ca, Mg, S), and with those whose content in the dissolved form is usually high (Si, Mn). Also, it is still not possible to determine carbide and nitride inclusions in steel using the spectral lines of C and N. The use of time-resolved spectroscopy can reduce the detection limits of the inclusions containing Si and, possibly, Mn. The use of an internal standard in the determination of inclusions also reduces the detection limits, but may distort the results. The use of solid-state linear radiation detectors instead of photomultipliers made it possible to develop a more reliable internal standard based on the background in the neighborhood of the spectral line. Verification of the results of the analysis is difficult owing to the lack of inclusion content reference samples. Further studies can expand the method’s detectable inclusion types list.

Advances in imaging instrumentation for nuclear cardiology

Advances in imaging instrumentation and technology have greatly contributed to nuclear cardiology. Dedicated cardiac SPECT cameras incorporating novel, highly efficient detector, collimator, and system designs have emerged with the expansion of nuclear cardiology. Solid-state radiation detectors incorporating cadmium zinc telluride, which directly convert radiation to electrical signals and yield improved energy resolution and spatial resolution and enhanced count sensitivity geometries, are increasingly gaining favor as the detector of choice for application in dedicated cardiac SPECT systems. Additionally, hybrid imaging systems in which SPECT and PET are combined with X-ray CT are currently widely used, with PET/MRI hybrid systems having also been recently introduced. The improved quantitative SPECT/CT has the potential to measure the absolute quantification of myocardial blood flow and flow reserve. Rapid development of silicon photomultipliers leads to enhancement in PET image quality and count rates. In addition, the reduction of emission–transmission mismatch artifacts via application of accurate time-of-flight information, and cardiac motion de-blurring aided by anatomical images, are emerging techniques for further improvement of cardiac PET. This article reviews recent advances such as these in nuclear cardiology imaging instrumentation and technology, and the corresponding diagnostic benefits.

Visible photoluminescence of color centers in LiF crystals for advanced diagnostics of 18 and 27 MeV proton beams

Solid-state radiation detectors based on the visible photoluminescence of radiation-induced F2 and F3+ color centers in lithium fluoride crystals have been used for advanced diagnostics of 18 and 27 MeV proton beams, produced by the TOP-IMPLART linear accelerator, which is under development for protontherapy applications at ENEA C.R. Frascati, Italy. Visible fluorescence microscopy was successfully used to read the latent proton beam images stored in the lithium fluoride crystals, thanks to high emission efficiency of the F2 and F3+ color centers obtained by simultaneous optical excitation in the blue spectral range. High intrinsic spatial resolution and wide dynamic range of these novel LiF detectors allow obtaining two-dimensional images of both the beam transverse intensity distribution and of the Bragg curve. By using a simple defect formation model that takes into account the energy released in the material and the saturation of defect concentration, not only the two-dimensional dose map was obtained from the beam transverse intensity distribution image, but also the full Bragg curve was reconstructed, allowing the thorough characterization of proton beams produced by the accelerator.

Determination of non-metallic inclusions in metal alloys by spark atomic emission spectrometry (review)

A review of publications regarding detection of non-metallic inclusions in metal alloys using optical emission spectrometry with single-spark spectrum registration is presented. The main advantage of the method - an extremely short time of measurement (~1 min) – makes it useful for the purposes of direct production control. A spark-induced impact on a non-metallic inclusion results in a sharp increase (flashes) in the intensities of spectral lines of the elements that comprise the inclusion because their content in the metal matrix is usually rather small. The intensity distribution of the spectral line of the element obtained from several thousand of single-spark spectra consists of two parts: i) the Gaussian function corresponding to the content of the element in a dissolved form, and ii) an asymmetric additive in the region of high intensity values ??attributed to inclusions. Their quantitative determination is based on the assumption that the intensity of the spectral line in the single-spark spectrum is proportional to the content of the element in the matter ablated by the spark. Thus, according to the calibration dependence constructed using samples with a certified total element content, it is possible not only to determine the proportions of the dissolved and undissolved element, but also the dimensions of the individual inclusions. However, determination of the sizes is limited to a range of 1 – 20 µm. Moreover, only Al-containing inclusions can be determined quantitatively nowadays. Difficulties occur both with elements hardly dissolved in steels (O, Ca, Mg, S), and with the elements which exhibit rather high content in the dissolved form (Si, Mn). It is also still impossible to determine carbides and nitrides in steels using C and N lines. The use of time-resolved spectrometry can reduce the detection limits for inclusions containing Si and, possibly, Mn. The use of the internal standard in determination of the inclusions can also lower the detection limits, but may distort the results. Substitution of photomultipliers by solid-state linear radiation detectors provided development of more reliable internal standard, based on the background value in the vicinity of the spectral line. Verification of the results is difficult in the lack of standard samples of composition of the inclusions. Future studies can expand the range of inclusions to be determined by this method.

Spatial response of synthetic microDiamond and diode detectors measured with kilovoltage synchrotron radiation.

To map the spatial response of four solid-state radiation detectors of types commonly used for radiotherapy dosimetry. PTW model 60016 Diode P, 60017 Diode E, 60018 Diode SRS, and 60019 microDiamond detectors were radiographed using a high resolution conventional X-ray system. Their spatial response was then investigated using a 0.1 mm diameter beam of 95 keV average energy photons generated by a synchrotron. The detectors were scanned through the beam while their signal was recorded as a function of position, to map the response. These 2D response maps were created in both the end-on and side-on orientations. The results show the location and size of the active region. End-on, the active area was determined to be centrally located and within 0.2 mm of the manufacturer's specified diameter. The active areas of the 60016 Diode P, 60017 Diode E, 60018 Diode SRS detectors are uniform to within approximately 5%. The 60019 microDiamond showed local variations up to 30%. The extra-cameral signal in the microDiamond was calculated from the side-on scan to be approximately 8% of the signal from the active element. The spatial response of four solid-state detectors has been measured. The technique yielded information about the location and uniformity of the active area, and the extra-cameral signal, for the beam quality used.

Proton beam spatial distribution and Bragg peak imaging by photoluminescence of color centers in lithium fluoride crystals at the TOP-IMPLART linear accelerator

Solid-state radiation detectors based on the photoluminescence of stable point defects in lithium fluoride crystals have been used for advanced diagnostics during the commissioning of the segment up to 27 MeV of the TOP-IMPLART proton linear accelerator for proton therapy applications, under development at ENEA C.R. Frascati, Italy. The LiF detectors high intrinsic spatial resolution and wide dynamic range allow obtaining two-dimensional images of the beam transverse intensity distribution and also identifying the Bragg peak position with micrometric precision by using a conventional optical fluorescence microscope. Results of the proton beam characterization, among which, the estimation of beam energy components and dynamics, are reported and discussed for different operating conditions of the accelerator.

Synthesis, Raman spectroscopy and dielectric properties of Ag:Mn co-doped nanostructured PbI2 for solid state radiation detectors

Microwave-assisted synthesis of pure and Ag: Mn co-doped PbI2 nanostructures have been reported for the first time. The structural and vibrational confirmations were carried out by X-ray diffraction and FT-Raman spectroscopic analysis. Furthermore, the EDX analysis confirms the presence of Ag and Mn in PbI2 nanostructures. No extra phase due to impurity in the synthesized nanostructures was observed. The nanosheets like morphology were confirmed by SEM study for all the synthesized products. The average thicknesses of the prepared nanosheets are found to be in the range of ∼30 nm–50 nm. The dielectric constant is found to be enriched by Mn and Ag: Mn co-doping in PbI2 compared to bulk value. The organized nanostructure with enhanced physical properties warrants the applications in optoelectronic devices and nanoscale radiation detectors.

SU‐D‐209‐01: Can Fluoroscopic Air‐Kerma Rates Be Reliably Measured with Solid‐State Meters?

Purpose:Ionization chambers remain the standard for calibration of air‐kerma rate measuring devices. Despite their strong energy‐dependent response, solid state radiation detectors are increasingly used, primarily due to their efficiency in making standardized measurements. To test the reliability of these devices in measuring air‐kerma rates, we compared ion chambers measurements with solid‐state measurements for various mobile fluoroscopes operated at different beam qualities and air‐kerma rates.Methods:Six mobile fluoroscopes (GE OEC models 9800 and 9900) were used to generate test beams. Using various field sizes and dose rate controls, copper attenuators and a lead attenuator were placed at the image receptor in varying combinations to generate a range of air‐kerma rates. Air‐kerma rates at 30 centimeters from the image receptors were measured using two 6‐cm3 ion chambers with electrometers (Radcal, models 1015 and 9015) and two with solid state detectors (Unfors Xi and Raysafe X2). No error messages occurred during measurements. However, about two months later, one solid‐state device stopped working and was replaced by the manufacturer. Two out of six mobile fluoroscopic units were retested with the replacement unit.Results:Generally, solid state and ionization chambers agreed favorably well, with two exceptions. Before replacement of the detector, the Xi meter when set in the “RF High” mode deviated from ion chamber readings by factors of 2 and 10 with no message indicating error in measurement. When set in the “RF Low” mode, readings were within −4% to +3%. The replacement Xi detector displayed messages alerting the user when settings were not compatible with air‐kerma rates.Conclusion:Air‐kerma rates can be measured favorably well using solid‐state devices, but users must be aware of the possibility that readings can be grossly in error with no discernible indication for the deviation.

Organic Single Crystals: An Essential Step to New Physics and Higher Performances of Optoelectronic Devices

Organic Single Crystals: An Essential Step to New Physics and Higher Performances of Optoelectronic Devices

Способ снижения пределов обнаружения неметаллических включений в металлических сплавах при их определении методом атомно-эмиссионной спектрометрии с искровым возбуждением

The determination of non-metallic inclusions and their size distribution in steels and alloys is regulated to be performed by the time-consuming optical or scanning electron microscopy methods. However, the development of pulse discrimination analysis – optical emission spectroscopy ( PDA-OES ) has made the on-line determination of inclusions possible. This technique is implemented with the industrial spectrometers registering the spectral lines’ intensities by photomultipliers ( PMT s). Using the linear solid-state radiation detectors instead of PMTs provides more information about spectra which opens up new possibilities to reduce the inclusions’ limits of detection and determine their chemical composition. This paper is devoted to the search for the new single-spark spectra-processing algorithms to use with the linear solid-state detectors based spectrometers. To reduce the inclusions’ detection limits, it is proposed to use the background near the spectral line as an internal standard. Filtering spectral line intensity peaks containing spectra was implemented to determine the background shape. Using the background as an internal standard allowed us to reduce the spectral line intensities’ standard deviation in the pulsogram (time dependence of spectral line intensity) by 10-50 %. To lower the errors, it was suggested to determine the dissolved content of an element by complementary integral spectrum. These decisions led to lower limits of detection for non-metallic inclusions and lower errors in element soluble/insoluble concentration determination. Keywords: PDA-OES, solid-state linear optical detectors, non-metallic inclusions, analysis of steels and alloys DOI: http://dx.doi.org/10.15826/analitika.2016.20.4.005 D.N. Bock 1, 2 , V.A. Labusov 1, 2, 3 1 Institute of Automation and Electrometry, SB RAS, 1 Academician Koptug ave, Novosibirsk, 630090, Russian Federation 2 VMK-Optoelektronika, 1 Academician Koptug ave, Novosibirsk, 630090, Russian Federation 3 Novosibirsk State Technical University, 20 K. Marksa ave, Novosibirsk, 630073, Russian Federation

Role of boron in formation of secondary radiation defects in silicon

Influence of boron impurities on electron-transport in crystalline silicon is well known because p-Si – basic semiconducting material of the modern microelectronics – usually is obtained by doping with B. It is too important to understand the mechanism interaction of B dopants with radiation defects in silicon to (i) develop effective radiation treatment technologies for electronic devices and integrated circuits, (ii) improve their radiation resistance, and (iii) design effective solid-state radiation sensors and detectors. Based on authors’ previous works the role of B-impurities in formation of secondary radiation defects in Si crystals is investigated. Dependences of these processes on isochronous annealing temperature (80–600 °C) are studied by using the Hall measurements of temperature-dependencies (100–300 K) of holes’ concentration and mobility in silicon before and after irradiation with 8 MeV electrons at the dose of 5∙10 15 cm –2 . Two main conclusions are made: boron atoms in silicon crystals (i) serve as extremely active sinks of radiation defects, and (ii) participate in space-charge-screening of the relatively high-conductive inclusions in form of clusters of radiation defects.

Photoluminescence of colour centres in lithium fluoride thin films: From solid-state miniaturised light sources to novel radiation imaging detectors

Luminescence properties of point defects in insulating materials are successfully used for solid state light sources and radiation detectors. Among them, colour centres in lithium fluoride, LiF, are well known for their application in tuneable lasers and dosimeters. Broad-band light-emitting F2 and F3+ electronic defects, stable at room temperature, are produced in LiF crystals and films by different kinds of radiation. Under blue optical pumping in their overlapping absorption bands, the efficient photoluminescence spans over the green–red visible spectral range. Novel LiF thin-film radiation imaging detectors based on the exploitation of the peculiar spectral characteristics of F2 and F3+ defects and of the optical properties and radiation sensitivity of the LiF material have been proposed and successfully tested for extreme ultraviolet radiation, soft and hard X-ray imaging, including micro-radiography of biological objects, even for in vivo samples. After exposure to X-rays, the latent images stored in the LiF thin layers by local formation of active defects are read with conventional and advanced optical fluorescence microscopes. Among the main advantages of the LiF thin-film imaging detectors, there are intrinsic very high spatial resolution, large field of view and wide dynamic range. Moreover, these solid state radiation detectors are easy to handle, as insensitive to ambient light, and no development process is needed. Recently their use has been extended to proton beam advanced diagnostics. In this paper, a short review of their properties, results and applications in X-ray biological imaging and proton dose-mapping is presented, underlying the great versatility and potentialities offered by LiF thin films, whose photoluminescence response can be improved through the choice of suitable substrates and growth conditions.

Photoluminescence of radiation-induced color centers in lithium fluoride thin films for advanced diagnostics of proton beams

Systematic irradiation of thermally evaporated 0.8 μm thick polycrystalline lithium fluoride films on glass was performed by proton beams of 3 and 7 MeV energies, produced by a linear accelerator, in a fluence range from 1011 to 1015 protons/cm2. The visible photoluminescence spectra of radiation-induced F2 and F3+ laser active color centers, which possess almost overlapping absorption bands at about 450 nm, were measured under laser pumping at 458 nm. On the basis of simulations of the linear energy transfer with proton penetration depth in LiF, it was possible to obtain the behavior of the measured integrated photoluminescence intensity of proton irradiated LiF films as a function of the deposited dose. The photoluminescence signal is linearly dependent on the deposited dose in the interval from 103 to about 106 Gy, independently from the used proton energies. This behavior is very encouraging for the development of advanced solid state radiation detectors based on optically transparent LiF thin films for proton beam diagnostics and two-dimensional dose mapping.

Surgeon radiation dose during complex endovascular procedures

Surgeon radiation dose during complex fluoroscopically guided interventions (FGIs) has not been well studied. We sought to characterize radiation exposure to surgeons during FGIs based on procedure type, operator position, level of operator training, upper vs lower body exposure, and addition of protective shielding. Optically stimulable, luminescent nanoDot (Landauer, Inc, Glenwood, Ill) detectors were used to measure radiation dose prospectively to surgeons during FGIs. The nanoDot dosimeters were placed outside the lead apron of the primary and assistant operators at the left upper chest and left lower pelvis positions. For each case, the procedure type, the reference air kerma, the kerma-area product, the relative position of the operator, the level of training of the fellow, and the presence or absence of external additional shielding devices were recorded. Three positions were assigned on the right-hand side of the patient in decreasing relative proximity to the flat panel detector (A, B, and C, respectively). Position A (main operator) was closest to the flat panel detector. Position D was on the left side of the patient at the brachial access site. The nanoDots were read using a microSTARii medical dosimetry system (Landauer, Inc) after every procedure. The nanoDot dosimetry system was calibrated for scattered radiation in an endovascular suite with a National Institute of Standards and Technology traceable solid-state radiation detector (Piranha T20; RTI Electronics, Fairfield, NJ). Comparative statistical analysis of nanoDot dose levels between categories was performed by analysis of variance with Tukey pairwise comparisons. Bonferroni correction was used for multiple comparisons. There were 415 nanoDot measurements with the following case distribution: 16 thoracic endovascular aortic repairs/endovascular aneurysm repairs, 18 fenestrated endovascular aneurysm repairs (FEVARs), 13 embolizations, 41 lower extremity interventions, 10 fistulograms, 13 visceral interventions, and 3 cerebrovascular procedures. The mean operator effective dose for FEVARs was higher than for other case types (P < .03), 20 μSv at position A and 9 μSv at position B. For all case types, position A (9.0 μSv) and position D (20 μSv) received statistically higher effective doses than position B (4 μSv) or position C (0.4 μSv) (P < .001). However, the mean operator effective dose for position D was not statistically different from that for position A. The addition of the lead skirt significantly decreased the lower body dose (33 ± 3.4 μSv to 6.3 ± 3.3 μSv) but not the upper body dose (6.5 ± 3.3 μSv to 5.7 ± 2.2 μSv). Neither ceiling-mounted shielding nor level of fellow training affected operator dose. Surgeon radiation dose during FGIs depends on case type, operator position, and table skirt use but not on the level of fellow training. On the basis of these data, the primary operator could perform approximately 12 FEVARs/wk and have an annual dose <10 mSv, which would not exceed lifetime occupational dose limits during a 35-year career. With practical case loads, operator doses are relatively low and unlikely to exceed occupational limits.

Surgeon Radiation Dose During Complex Endovascular Procedures

Surgeon radiation dose during complex endovascular procedures (CEPs) has not been well studied. We sought to characterize radiation exposure to surgeons during CEPs based on procedure type, operator position, level of operator training, upper vs lower body exposure, and the addition of protective shielding. Optically stimulable, luminescent nanoDot (Landauer Inc) detectors were used to measure radiation dose prospectively to surgeons during CEPs. NanoDot dosimeters were placed outside the lead apron of the primary and assistant operator at the left upper chest and left lower pelvis positions. For each case, procedure type, reference air kerma (RAK), kerma area product (KAP), the relative position of the operator, level of training of the fellow, and presence or absence of external additional shielding devices were recorded. Three positions were assigned on the right hand side of the patient in decreasing relative proximity to the flat panel detector (FPD) as A, B, and C, respectively. Position A (main operator) was closest to the FPD. Position D was on the left side of the patient at the brachial access site. NanoDots were read using a Microstar II medical dosimetry system (Landauer Inc) after every procedure. The nanoDot dosimetry system was calibrated for scattered radiation in an endovascular suite with a NIST-traceable solid state radiation detector (Piranha T20, RTI). Comparative statistical analyses of nanoDot dose levels between categories was performed using analysis of variance with Tukey pairwise comparisons. Bonferroni correction was used for multiple comparisons. There were 415 nanoDot measurements with the following case distribution: 16 thoracic endovascular aortic repairs or endovascular aneurysm repairs, 18 fenestrated endovascular aneurysm repairs (FEVARs), 13 embolizations, 41 lower extremity, 10 fistulograms, and 13 viscerals. The mean operator dose for FEVARs was statistically higher than for other case types (P < .03), 15 μSv at position A and 11 μSv at position B. For all case types, positions A (8.7 ± 2.7 μSv) and D (14.4 ± 7.8 μSv) received statistically higher effective doses than B (3.9 ± 2.7 μSv; P < .001 or C (0 mGy). However, the mean operator dose for position D was not statistically different from position A. The addition of the lead skirt significantly decreased the lower body dose (33 ± 3.4 μSv to 6.3 ± 3.3 μSv) but not the upper body dose (6.5 ± 3.3 μSv to 5.7 ± 2.2 μSv). The use of ceiling-mounted shielding did not affect the nanoDot dose. There was no difference in the operator dose observed based on level of training when the fellow was in position A. KAP was the better predictor of operator radiation dose compared with RAK. The mean KAP for all cases was 330 Gycm2, and the regression coefficient for operator dose to KAP was 0.021 ± 0.003 μSv/Gycm2 for position A and 0.015 ± 0.003 μSv/Gycm2 for B. Surgeon radiation dose during CEPs depends on case type, operator position, and table skirt use, but not on the level of fellow training. On the basis of this data, the primary operator could perform ∼12 FEVARs per week and have an annual dose of <10 mSv, which would not exceed lifetime occupational dose limits during a 35-year career. Excluding FEVARs with the above case mix, the primary operator could perform ∼40 CEPs per week and stay within regulatory limits. With practical case loads, operator doses are relatively low and unlikely to exceed occupational limits.

Dose response of selected solid state detectors in applied homogeneous transverse and longitudinal magnetic fields.

MR-Linac devices under development worldwide will require standard calibration, commissioning, and quality assurance. Solid state radiation detectors are often used for dose profiles and percent depth dose measurements. The dose response of selected solid state detectors is therefore evaluated in varying transverse and longitudinal magnetic fields for this purpose. The Monte Carlo code PENELOPE was used to model irradiation of a PTW 60003 diamond detector and IBA PFD diode detector in the presence of a magnetic field. The field itself was varied in strength, and oriented both transversely and longitudinally with respect to the incident photon beam. The long axis of the detectors was oriented either parallel or perpendicular to the photon beam. The dose to the active volume of each detector in air was scored, and its ratio to dose with zero magnetic field strength was determined as the "dose response" in magnetic field. Measurements at low fields for both detectors in transverse magnetic fields were taken to evaluate the accuracy of the simulations. Additional simulations were performed in a water phantom to obtain few representative points for beam profile and percent depth dose measurements. Simulations show significant dose response as a function of magnetic field in transverse field geometries. This response can be near 20% at 1.5 T, and it is highly dependent on the detectors' relative orientation to the magnetic field, the energy of the photon beam, and detector composition. Measurements at low transverse magnetic fields verify the simulations for both detectors in their relative orientations to radiation beam. Longitudinal magnetic fields, in contrast, show little dose response, rising slowly with magnetic field, and reaching 0.5%-1% at 1.5 T regardless of detector orientation. Water tank and in air simulation results were the same within simulation uncertainty where lateral electronic equilibrium is present and expectedly differed at the beam edge in transverse field orientations only. Due to the difference in design, the two detectors behaved differently. When transverse magnetic fields are present, great care must be taken when using diamond or diode detectors. Dose response varies with relative detector orientation, magnetic field strength, and between detectors. This response can be considerable (∼20% for both detectors). Both detectors in longitudinal fields exhibit little to no dose response as a function of magnetic field. Water tank simulations seem to suggest that the diode detector is better suited to general beam commissioning, and each detector must be investigated separately.