Solid State Dosimeters Research Articles

Radiophotoluminescence response of LiF:Mg,Ti pellets irradiated with clinical proton beams in the 70–200 MeV energy range

Lithium fluoride doped with Mg and Ti (LiF:Mg,Ti) has been used for several decades as thermoluminescent dosimeter material, but recently also its radiophotoluminescence has been investigated for applications in dosimetry. In this work, LiF:Mg,Ti pellets (TLD-100) were irradiated in a water phantom at CNAO (Pavia, Italy) with therapeutic proton beams at five energies from 70 to 200 MeV in the dose range from 2 to 20 Gy. After irradiation, their visible radiophotoluminescence spectra were measured in controlled conditions and the spectrally-integrated red emission response of radiation-induced color centers has been investigated. The radiophotoluminescence signal, excited by a 445 nm continuous wave laser, was integrated within a 50 nm-wide band around the emission peak of the F2 color centers, located around 670 nm in LiF. The spectrally-integrated signal of the samples irradiated at the energy of 147.7 MeV exhibited a linear dependence with dose. Moreover, this radiophotoluminescence response appears independent from Linear Energy Transfer in the range from 0.8 to 1.6 keV/μm in all the samples irradiated at the dose of 5 Gy. Such independence was found up to 10.3 keV/μm in samples irradiated within two spread out Bragg peaks made of 36 energy components in the entire investigated proton energy range. The radiophotoluminescence response of the TLD-100 pellets was compared to that of nominally-pure LiF crystals irradiated in the same conditions, which show a similar behavior. The results are encouraging for the exploitation of TLD-100 pellets as passive solid-state radiophotoluminescent dosimeters for proton therapy.

Diamond detectors’ response to intense high-energy electron pulses

Diamond crystals are characterised by wide band gap and high binding energy, making them suitable as solid-state particle detectors, beam-loss monitors and dosimeters in high-radiation environments, such as particle colliders. In order to use them as radiation and beam-loss monitors, our diamond detectors are calibrated in steady conditions with different radiation sources, comparing the measurement results with dedicated simulations. However large radiation bursts may lead to a non-linear signal response. For this purpose we studied their transient response to collimated, sub-picosecond, ∼ 1 GeV electron beam bunches, with a bunch charge of tens of pC, provided by the FERMI electron linac in Trieste. In these experimental conditions the ionisation generates large charge carrier density in the diamond bulk. This high charge causes a transient modification of diamond electrical properties, which affects the output signal shape. The observed signal evolution in the time domain shows fair agreement with a two-step numerical simulation of the diamond time response to these intense high-energy pulses.

In-depth characterisation of diamond sensors for dosimetry in beam-loss monitoring

Owing to its excellent radiation hardness, diamond has been widely used for solid-state particle detectors and dosimeters in harsh radiation environments. In order to assess the crystal quality and the response of our devices, we carried out several tests using different radiation sources. We devised a current-to-dose-rate calibration method that employs a silicon diode as a reference, to greatly reduce uncertainties associated with the source activity and with the setup simulation. The method has been validated by measuring the calibration factors with X and β radiation, spanning a dose-rate range from hundreds of nrad/s to tens of rad/s. Here we report the results for a set of tests and calibrations performed on ten new diamond detectors recently assembled and tested. The new results include several refinements of the measurements and of their interpretation. We also briefly describe an ongoing irradiation of the devices with 1-GeV electrons from the linac of the FERMI@Elettra FEL in Trieste.

Relative dose-response from solid-state and gel dosimeters through Monte Carlo simulations

The present work compared the relative absorbed dose of some dosimetric materials, for energies of 250 kV and 6 MV, using PENELOPE and MNCPX codes. The composition of each material GD-301, TLD-100, MAGIC, and MAGAT were simulated and disposed of in a phantom filled with water following reference conditions recommended by the TRS-398 protocol. Percentage depth dose was used as a parameter of comparison. Since the obtained results with both codes were found a maximum difference of up to 2 % when compared the water material with experimental data before 6cm were found to a maximum difference of up to 2.2% for 6 MV and 5.5 % for 250 kV. Ratios between simulated PPD and experimental PDD values showed a maximum difference in the build-up region, for 6 MV, due to highsensitivityive from the incident fluency in the simulated and experimental conditions. The ratios for 250 kV showed significant differences from the simulated solid-state rather than gel dosimeters, due to its low energy, depth angular dependence from the solid-state dosimeter, as corroborating by literature. Even the differences showed for both codes, especially for lower energy, due to cross-the section database that implied the interaction probability for each Monte Carlo code, this method has been widely used to model radiation transport in several applications in medical physics, especially in dosimetry.

Visible radiophotoluminescence of colour centres in lithium fluoride: from lasers to versatile radiation sensors

The peculiar photoluminescence characteristics of radiation-induced colour centres in lithium fluoride (LiF), well known for applications in optically-pumped tuneable lasers and broad-band miniaturised light-emitting photonic devices operating at room-temperature, are under exploitation in passive imaging detectors and dosimeters based on visible radiophotoluminescence in LiF crystals and polycrystalline thin films. Their high intrinsic spatial resolution, wide dynamic range and large field of view, combined with easy handling, ambient-light operation and no development need, allow to successfully extend their use from X-ray imaging to proton-beam advanced diagnostics and dosimetry, even at those low dose values that are typical of hadrontherapy. After exposure, the latent images stored in LiF as local formations of F2 and F3 + aggregate defects are read with an optical fluorescence microscope under illumination in the blue spectral range. Their visible emission intensity was found to be linearly proportional to the dose over at least three orders of magnitude, so that bi-dimensional LiF solid-state dosimeters based on spectrally-integrated radiophotoluminescence reading can be envisaged. Taking advantage of the low thickness of LiF thin films, transversal proton beam dose mapping was demonstrated at low proton energies, even at high doses. Recent results and advances concerning LiF crystals and polycrystalline thin film characterisation in the linearity range are presented and discussed with the aim of highlighting challenges related to increasing the LiF film detector radiation sensitivity to both particles (protons) and photons (X-rays), although therapeutic dose values typical of clinical radiotherapy are still a big challenge.

Feasibility of determining mammography dose using LuSy dosimeter

Mammography is a radiological examination that utilises low-energy X-ray to detect breast cancer. The techniques include full-field digital mammography (FFDM) and digital breast tomosynthesis (DBT), which produce 2D and 3D breast images, respectively. Mean glandular dose (MGD) is used to describe the dose delivered by these techniques because it estimates the photon absorption by glandular tissues in the breast. This study aims to calibrate, characterise and determine the feasibility of measuring MGD using an in-house developed, real-time fibre-optic dosimeter called the LuSy dosimeter. LuSy was calibrated against a solid-state mammography dosimeter for three target-filter combinations of W/Rh, W/Ag and W/Al. Subsequently, characterisation towards mammography radiation was carried out. Finally, MGD was measured using LuSy and subsequently compared with the readings of a solid-state detector and those estimated by the mammography machine. The measured calibration coefficient was 342.10, 380.35 and 447.68 counts/mGy for W/Rh, W/Ag and W/Al target-filter combinations, respectively. For MGD, both LuSy and the mammography dosimeter measured a higher dose compared with the machine console. The mean deviation between LuSy and machine console was 14.72%. Meanwhile, the mean deviation between the mammography dosimeter and the machine console was 19.5%. In conclusion, the LuSy may be calibrated to measure low-energy X-ray, and its MGD reading is comparable with a solid-state dosimeter.

Thermal drift reduction in photodiode dosimeters with switching bias

The effect of temperature on dosimetric measurements is a major limitation of solid-state dosimeters. This is especially true for PIN photodiode dosimeters, where the dark current depends exponentially on temperature. To minimize this effect, a compensation method is presented that relies on the diode structure itself without the need for an external sensor or device. During irradiation, the photodiode is periodically switched from reverse to forward polarization to determine the temperature of the device. This measurement is based on the linear dependence between the temperature and the forward voltage of the diode when it is operated at constant current. An electronic circuit implementing this procedure was developed and used for experimental characterization of the response to radiation of the BPW34S Si PIN photodiode. The proposed procedure reduced the uncertainty due to thermal drift by a factor of 7.5. In addition, an average dose rate sensitivity of 12 ± 2 nC/cGy was measured, with a sensitivity degradation below 2% for the irradiation cycle of 21.4 Gy performed under a 6 MV photon beam. We have shown that a p-n junction can be successfully used to compensate for the temperature effect on the dosimetric measurement.

A multi-institutional comparison of dosimetric data for a 0.35 T MR-linac

Objective. A comparison of percent depth dose (PDD) curves, lateral beam profiles, output factors (OFs), multileaf collimator (MLC) leakage, and couch transmission factors was performed between ten institutes for a commercial 0.35 T MR-linac. Approach. The measured data was collected during acceptance testing of the MR-linac. The PDD curves were measured for the 3.32 × 3.32 cm2, 9.96 × 9.96 cm2, and 27.20 × 24.07 cm2 field sizes. The lateral beam profiles were acquired for a 27.20 × 24.07 cm2 field size using an ion chamber array and penumbra was defined as the distance between 80% of the maximum dose and 20% of the maximum dose after normalizing the profiles to the dose at the inflection points. The OFs were measured using solid-state dosimeters, whereas radiochromic films were utilized to measure radiation leakage through the MLC stacks. The relative couch transmission factors were measured for various gantry angles. The variation in the multi-institutional data was quantified using the percent standard deviation metric. Main results. Minimal variations (<1%) were found between the PDD data, except for the build-up region and the deeper regions of the PDD curve. The in-field region of the lateral beam profiles varied <1.5% between different institutions and a small variation (<0.7 mm) in penumbra was observed. A variation of <1% was observed in the OF data for field sizes above 1.66 × 1.66 cm2, whereas large variations were shown for small-field sizes. The average and maximum MLC leakage was calculated to be <0.3% and <0.6%, which was well below the international electrotechnical commission (IEC) leakage thresholds. The couch transmission was smallest for oblique beams and ranged from 0.83 to 0.87. Significance. The variation in the data was found to be relatively small and the different 0.35 T MR-linacs were concluded to have similar dosimetric characteristics.

Dose response of visible color center radiophotoluminescence in lithium fluoride crystals irradiated with a reference 60Co gamma beam in the 1–20 Gy dose range

The visible radiophotoluminescence response of radiation-induced stable F2 and F3+ color centers in nominally pure lithium fluoride crystals, irradiated with a reference 60Co gamma beam in the 1–20 Gy dose range, was carefully investigated. After irradiation, the Stokes-shifted emission spectra of the colored crystals were measured as a function of time under continuous laser excitation at 445 nm and in stationary conditions. The F2 radiophotoluminescence intensity remains constant; the signal, spectrally integrated in a 50 nm-wide interval centered on the F2 emission peak at 670 nm, exhibited a linear dependence on the absorbed dose with a good signal-to-noise ratio, stability for multiple readout and long storage times. Combined with our previous investigations after irradiation at similar doses with low-energy protons and clinical X-ray beams, these experimental results confirm the feasibility of passive solid-state dosimeters for radiotherapy based on color center radiophotoluminescence in nominally pure lithium fluoride crystals.

Дозиметрическое сопровождение биологических экспериментов на примере семян салата при экспонировании на биоспутнике «БИОН-М» No 1

The cytogenetic characteristics of Lactuca sativa lettuce seeds exposed in a package located inside the Bion-M1 biosatellite were studied. The absorbed dose according to solid-state dosimeters placed inside the package was 58 ± 3 mGy. There was a significant (p ≤ 0,001) increase in the percentage of cells with chromosome aberrations, cells with multiple aberrations, as well as the percentage of chromosomal bridges and fragments; the percentage of chromatid bridges and fragments was not significantly increased. At the same time, the seed vigor and germinating ability of the flight samples remain at the control level of 99–100 %.

Colloidal processing of thulium-yttria microceramics

The development of new dosimetric materials is essential for the safe and effective use of nuclear technology. In the present study, an eco-friendly bio-prototyping approach was developed for preparing thulium-yttria microceramics with potential applications in radiation dosimetry. Micro-powder compacts were obtained by casting colloidal thulium-yttria suspensions prepared with 20 vol% particles in thin-walled tube templates. Samples were sintered at 1600 °C for 2 h under the environmental pressure and atmosphere to obtain thulium-yttria microceramics with dimensions of 3.33 ± 0.01 mm × 2.27 ± 0.01 mm (height × diameter), as well as a cubic C-type structure, pycnometric density of 4.79 g cm−3 (95.61% theoretical density), and surface microstructure comprising hexagon-like grains bonded at the boundaries. The use of thulium as an activator of yttria greatly improved the electron paramagnetic resonance (EPR) response of the microceramics, where the main EPR peak (p1) was recorded at 351.24 mT and the g factor was 2.0046. The innovative findings obtained in this study may facilitate the production of new solid state dosimeters.

A New Method on Kerma Estimation in Mammography Screenings

Background: Given the extensive use and preferred diagnostic method in common mammography tests for screening and diagnosis of breast cancer, there is concern about the increased dose absorbed by the patient due to the sensitivity of the breast tissue.Objective: This study aims to evaluate the entrance surface air kerma (ESAK) before irradiation to the patient through its estimation.Material and Methods: In this descriptive paper, firstly, a phantom was used to measure some data, including ESAK, Kvp, mAs, HVL, and type of filter/target. Secondly, the MultiLayer Perceptron (MLP) neural network model was trained with Levenberg-Marquardt (LM) backpropagation training algorithm and finally, ESAK was estimated.Results: Based on results obtained from the program in different neuron numbers, it was found that the number of 35 neurons is the most optimal value, offering a regression coefficient of 95.7%. The Mean Squared Error (MSE) for all data was 0.437 mGy and accounting for 4.8% of the output range changes, predicting 95.2% accuracy in the present research.Conclusion: Using neural networks in ESAK prediction, the method proposed in the present research leads to the possible ESAK estimation of patients before X-Ray. The results suggested that the regression coefficient represented 4.3% difference between the kerma measured by solid-state dosimeter in the radiation field and the value predicted in the research. In comparison with the Monte-Carlo simulation method, this method has better accuracy.

Investigation of single-shot beam quality measurements using state of the art solid-state dosimeters for routine quality assurance applications in mammography

<h2>Abstract</h2><h3>Purpose</h3> To assess if single shot acquisitions with solid-state dosimeters as well as Robson's method could replace ionization chambers for tube output and HVL measurements, saving medical physicists time. <h3>Material and methods</h3> The energy responses of 4 solid-state dosimeters with automatic calculation of HVL were compared to ionization chamber measurements. Five anode/filter combinations were tested: Mo/Mo, Mo/Rh, Rh/Rh, W/Rh and W/Ag, from 24kVp to 35kVp. Tube output was measured free in air. HVL was measured using the solid-state dosimeters (single-shot acquisition), then manually with aluminum sheets and finally using the parametrization method of Robson. <h3>Results</h3> Deviations in tube output and HVL related to energy response in SSD were small in the 25–32 kVp range, and for tube output typically within 3%. Extrapolation using the Robson parametrization was within 5%, except for one device and for all W/Rh. Deviations of the HVL using the single shot approach were within 10% of the gold standard data. Larger deviations were found at the extreme tube voltages of 24kVp and 35kVp (maximum of 24%). <h3>Conclusion</h3> With the assumption that deviations in tube output of 5% and for HVL of 10% are acceptable, all tested solid state dosimeters met this criterion in the tube voltage range of 26kVp to 32kVp. Robson's method worked well for the spectra for which the method was developed, making both alternative approaches trustworthy for routine quality assurance purposes.

Numerical simulation of measurements in radiation technologies

Radiation plays a very important role in the life of humans. Measurements in radiation technologies and radiation processes are very important. Usually measurements in radiation technologies are made with dosimeters of various types: solid state dosimeters, liquid dosimeters and gaseous dosimeters. Dose measurements are based on different principles: temperature increase, collection of electric charge, development of gases, accumulation of free radicals, trapping of electron in the matrix, color change, change of solution conductivity, radiation chemical oxidation, radiation chemical reduction. To measure absorbed doses the dosimetry system should be used which consists of dosimeters, measurement instrumentation, the calibration curve, reference standards and procedure for the system’s use.&#x0D; Computer processing power has increased rapidly and significantly over the past decades. Modern computers with proper software and mathematical methods allow to simulate very complicated processes, for example passage of ionizing radiation through the matter.&#x0D; Article shows that GEANT4 can be used for numerical simulations to determine the absorbed doses, dose rates, and other values inside irradiated objects under radiation. The relative uncertainty is up to 11.8%. Simulation of radiation processing of complex objects can be performed with good accuracy. In order to use numerical simulations to measure radiation, metrological support should be developed.

Calibration of diamond detectors for dosimetry in beam-loss monitoring

Artificially-grown diamond crystals have unique properties that make them suitable as solid-state particle detectors and dosimeters in high-radiation environments. We have been using sensors based on single-crystal diamond grown by chemical vapour deposition for dosimetry and beam-loss monitoring at the SuperKEKB collider. Here we describe the assembly and the suite of test and calibration procedures adopted to characterise the diamond-based detectors of this monitoring system. We report the results obtained on 28 detectors and assess the stability and uniformity of response of these devices.

Occupational doses to the eye lens in pediatric and adult noncardiac interventional radiology procedures.

To assess occupational lens exposure in a mixed interventional radiology department, comparing pediatric and adult procedures. To analyze the correlation between the lens dose and the doses measured at the chest and collar level and the kerma-area product (PKA ). For 17months, three radiologists performing both pediatric and adult interventions were monitored by means of 14 dosimeters per worker: 12 single-point optically stimulated luminescent (OSL) dosimeters calibrated in terms of Hp (0.07) were placed on the inside and outside of two pairs of lead glasses, one for pediatric procedures and one for adult interventions; another whole-body OSL dosimeter calibrated in terms of Hp (10) was placed over the thyroid shield; finally, an additional active solid-state dosimeter, also calibrated for Hp (10), was worn on the chest, over the apron. Furthermore, a database was created to register the demographic and dosimetric data of the procedures, as well as the name of the radiologist acting as first operator. For the three radiologists, who performed 276-338 procedures/year (20% pediatric), cumulative annual doses to the left bare eye exceeded 20mSv (21-61mSv). Considering the glasses' protection, annual doses exceeded 6mSv (13-48mSv) for both eyes. No important differences were observed in lens dose per procedure between pediatric and adult interventions (0.16 vs 0.18, 0.12 vs 0.09, and 0.07 vs 0.07mSv), although lens dose per PKA was 4.1-4.5 times higher in pediatrics (5.8 vs 1.3, 3.3 vs 0.8, and 2.6 vs 0.6µSv/Gy·cm2 ) despite a similar use of the ceiling-suspended screen. Lens doses were highly correlated with collar readings (with Pearson coefficients [r] ranging from 0.86 to 0.98) and with chest readings (with r ranging from 0.75 to 0.93). However, slopes of the linear regressions varied greatly among radiologists. There is real risk of exceeding the occupational dose limit to the eye lens in mixed interventional radiology rooms if radiation protection tools are not used properly. Regular monitoring of the lens dose is recommended, given lens exposure might easily exceed 6mSv/yr. Using a collar dosimeter for this purpose might be suitable if it is preceded by an individualized regression analysis. The same radiation protection measures should be applied to interventional radiologists regardless of whether they are treating pediatric or adult patients.

Quality control measurements for mobile X-ray unit through a solid state detector

The tests of quality control for equipments used in radiology departments are essential both functionality of the equipment and for accuracy dose in the patient. The mobile digital x-ray equipment has as one of its main benefits its mobility, which allows the carrying out of examinations in the patient’s bed that has certain physical limitations. It should be taken into account, however, that hospital beds were not normally designed with the necessary details to protect the radiological environment from where radiography procedures are performed. Therefore, the need for an efficient quality control of the equipment is justified, the preliminary measurements of the present work were based on ANVISA’s guide 453 from Brazil, regarding conventional radiography equipment. Thus, some quality control tests were determined using the solid state dosimeter. For the accomplishment of this study, the tests of tube voltage accuracy and reproducibility, half valuelayer (HVL) and effective energy, air kerma and air kerma rate were performed, with their associated errors calculated. The tests were performed with the aid of the black piranha apparatus to obtain the values of tension, dose and HVL. The obtained results from the performance of each test showed that all are in agreement withthe ANVISA’s guide 453 recommendation, and could be applied in a possible development of a quality control guide specific to the characteristics of a mobile radiograph.

Performance testing of dosimeters used in interventional radiology: Results from the VERIDIC project

Interventional procedures in radiology and cardiology are associated with high dose to the patient. Accurate dosimetry is essential and calibration of the equipment is a means to provide the necessary accuracy of dose assessment.The objective of this work is to investigate the performance of dosimeters used in interventional procedures in different standard and non-standard X-ray radiation qualities, and to investigate potential uncertainties related to dose measurements, thus improving accuracy of patient dosimetry in interventional procedures.Four new reference radiation qualities dedicated to interventional cardiology applications have been established, allowing calibration of dosimeters used in clinical conditions with appropriate traceability to primary standards. Testing of solid-state semiconductor detectors and thermoluminescent dosimeter properties, e.g. influence of photon energy, angle of incidence and dose rate, was performed in the standard and non-standard radiation qualities.Both dosimeter types showed good performance in the non-standard beams during all performance tests. Solid-state dosimeters displayed weak dependence on energy, angle of incidence and dose rate, in the range defined by the manufacturer and requirements of the international standard. Thermoluminescent dosimeters displayed excellent linearity and angular dependence. The influence of energy dependence on measurement uncertainty can be reduced if appropriate radiation quality is selected for calibration.

Consistency of small-field dosimetry, on and off axis, in beam-matched linacs used for stereotactic radiosurgery.

PurposeStereotactic radiosurgery (SRS) can be delivered with a standard linear accelerator (linac). At institutions having more than one linac, beam matching is common practice. In the literature, there are indications that machine central axis (CAX) matching for broad fields does not guarantee matching of small fields with side ≤2 cm. There is no indication on how matching for broad fields on axis translates to matching small fields off axis. These are of interest to multitarget single‐isocenter (MTSI) SRS planning and the present work addresses that gap in the literature.MethodsWe used 6 MV flattening filter free (FFF) beams from four Elekta VersaHD® linacs equipped with an Agility™ multileaf collimator (MLC). The linacs were strictly matched for broad fields on CAX. We compared output factors (OPFs) and effective field size, measured concurrently using a novel 2D solid‐state dosimeter “Duo” with a spatial resolution of 0.2 mm, in square and rectangular static fields with sides from 0.5 to 2 cm, either on axis or away from it by 5 to 15 cm.ResultsAmong the four linacs, OPF for fields ≥1 × 1 cm2 ranged 1.3% on CAX, whereas off axis a maximum range of 1.9% was observed at 15 cm. A larger variability in OPF was noted for the 0.5 × 0.5 cm2 field, with a range of 5.9% on CAX, which improved to a maximum of 2.3% moving off axis. Two linacs showed greater consistency with a range of 1.4% on CAX and 2.2% at 15 cm off axis. Between linacs, the effective field size varied by <0.04 cm in most cases, both on and off axis. Tighter matching was observed for linacs with a similar focal spot position.ConclusionsVerification of small‐field consistency for matched linacs used for SRS is an important task for dosimetric validation. A significant benefit of concurrent measurement of field size and OPF allowed for a comprehensive assessment using a novel diode array. Our study showed the four linacs, strictly matched for broad fields on CAX, were still matched down to a field size of 1 x 1 cm2 on and off axis.

Review of the thermoluminescent dosimetry method for the environmental dose monitoring

Passive solid state dosimeters, such as thermoluminescence dosimeters, provide integrated measurement of the total dose and are widely used in environmental monitoring programs. The objective of this paper is to provide a comprehensive review on the use of thermoluminescent dosimetry methods for monitoring radiation dose in the environment. The article presents the part of the research results of the project PREPAREDNESS (EMPIR 2016 call for Metrology for Environment joint research project) with a particular objective to harmonize procedures used by dosimetry services, relevant authorities and Institutes across the Europe. To achieve this, different monitoring routines that are based on passive environ mental dosimetry methods are investigated. Differences in performing specific steps such as preheating, reading, annealing, minimizing fading, and others, are analyzed. The investigation was performed by means of qualitative literature review that showed the lack of information about specific steps. The conclusion of this work is that thermoluminescent dosimetry measurement system has to be type-tested even though the testing procedure is complicated. In addition to this, control dosimeters should be introduced, International Organization for Standardization protocols should be followed during calibration, and finally, parameters influencing the measurement uncertainty have to be identified and well understood in order to pro duce ac cu rate dose measurement results.