Response Dose Research Articles

Characterization of a thin photodiode as a routine dosimeter for low-dose radiation processing applications

The characterization of a dosimetry system based on a commercial PIN photodiode as a routine dosimeter in a 60Co industrial facility is reported. The main parameters of the dose rate response (repeatability, reproducibility, and angular dependence) and the dose response (dependence on both dose rate and accumulated dose) are investigated. The results obtained, within a dose rate range of 3.7–52.8 Gy/h and doses up to 200 Gy, fully adhere to the standard protocols established for radiation processing dosimetry. The diode performance as a routine dosimeter is validated by the good overall agreement with radiochromic films and alanine dosimetry.

Luminescence and dose-rate response properties of Pr-doped Bi4Ge3O12 scintillators

In recent years, there has been increasing demand for a scintillator showing near-infrared (NIR) luminescence owing to the potential for radiation monitoring applications. In this study, Pr-doped Bi4Ge3O12 (BGO) single crystals were prepared by the floating zone method to explore candidates as a NIR scintillator, and the luminescence and dose-rate response properties of Pr-doped BGO were studied. Both photoluminescence and scintillation peaks appeared at 400–600 nm due to Bi3+, and sharp emission peaks by Pr3+ were also confirmed at 480–1100 nm, with consistent decay times. Further, to investigate performance as a scintillation detector, a linearity of the response to X-ray exposure dose rate was evaluated. Among the samples, the 0.5% Pr-doped BGO showed the highest sensitivity with the lowest detection limit of 0.006 Gy/h.

An Active Dose Measurement Device for Ultra-short, Ultra-intense Laser Facilities.

Ultra-short, ultra-intense laser facilities could produce ultra-intense pulsed radiation fields. Currently, only passive detectors are fit for dose measurement in this circumstance. Since the laser device could generate a dose up to tens of mSv outside the chamber in tens of picoseconds, resulting in a high instantaneous dose rate of ~107 Sv s-1, it is necessary to perform real-time dose measurement to ensure the safety of nearby workers. Due to fast response and excellent radiation resistance, a diamond-based dose measurement device was designed and developed, and its dose-rate response and its feasibility for such occasions were characterized. The measurement results showed that the detector had a good dose-rate linearity in the range of 3.39 mGy h-1 to 10.58 Gy h-1 for an x-ray source with energy of 39 keV to 208 keV. No saturation phenomenon was observed, and the experimental results were consistent with the results obtained from Monte Carlo simulation. The charge collection efficiency was about 80%. Experimental measurements and simulations with this dose measurement device were carried out based on the "SG-II" laser device. The experimental and simulation results preliminarily verified the feasibility of using the diamond detector to measure the dose generated by ultra-short, ultra-intense laser devices. The results provided valuable information for the follow-up real-time dose measurement work of ultra-short, ultra-intense laser devices.

A competitive radioluminescence material - LiF:Mg,Cu,P for real-time dosimetry

Currently, common radioluminescent (RL) materials have their own advantages and disadvantages in real-time dosimetry. The most attractive RL materials are tissue equivalent materials with stable sensitivity, weak afterglow, and a wide dose-rate linear range. LiF has a low effective atomic number, and previous studies have reported the RL sensitivity of LiF:Mg,Ti is dose-dependent. LiF:Mg,Cu,P can also emit RL during irradiation, which may be used for real-time dose monitoring. The purpose of this paper is to investigate dose characteristics of RL in LiF:Mg,Cu,P based on a developed optical fiber system and a commercial TL/OSL reader (Risφ TL/OSL-DA-20C/D). The results indicated that the RL sensitivity of LiF:Mg,Cu,P is not as good as Al2O3:C, but comparable to LiF:Mg,Ti. It can be inferred that LiF:Mg,Cu,P is suitable for high dose rate measurements. LiF:Mg,Cu,P showed almost a constant sensitivity to absorbed dose and a weak afterglow signal, which implies the accurate dose rates can be obtained quickly without sensitivity corrections. In addition, LiF:Mg,Cu,P has a good linear dose-rate response ranging from 0.76 mGy/h to 8.02 Gy/h, similar to LiF:Mg,Ti, and a superior repeatability (∼1.36%) to LiF:Mg,Ti. In conclusion, LiF:Mg,Cu,P is a competitive RL material for real-time dosimetry with its own advantages.

Flexible Scintillation Silica Fiber with Engineered Nanocrystals for Remote Real-Time X-ray Detection.

Scintillation fibers based on rare-earth ion-doped crystal materials have attracted significant attention for applications in a wide range of areas from security to healthcare. However, the scintillation performance of crystal fibers is severely limited owing to the complex preparation process. Here, we report a modified preparation process of the transparent Ce/Tb co-doped yttrium pyrosilicate (YPS) nanocrystal silica fiber for the first time, which was fabricated by the CO2 laser-heated method assisted with optimal thermal annealing. An YPS nanocrystal phase with an average size of approximately 38 nm is obtained by controlling the diffusion concentration of SiO2 in the fiber core region. Both Ce3+ and Tb3+ ions were successfully embedded into YPS nanocrystals, which enhanced the energy transfer with an efficiency of 59.87% between the dopants as well as brighter green light emission. Furthermore, the X-ray-excited remote radioluminescence response of the obtained YPS nanocrystal fiber with a length of 20 m was approximately 1 order of magnitude larger than that of the precursor fiber, while the dose rate response exhibited excellent linearity. It is believed that the novel transparent YPS nanocrystal-doped silica optical fibers, combined with their excellent fluorescent properties, could be promising candidates for scintillators, fiber lasers, and phosphors.

Sensitivity and specificity analysis of 2D small field measurement array: Patient-specific quality assurance of small target treatments and spatially fractionated radiotherapy.

PurposeThe aim of this paper is to describe the tests carried out on a SRSMapCheck array, to verify its reliability and sensitivity for quality assurance (QA) of high gradient treatments as an alternative system to the use of high spatial resolution detectors, such as gafchromic film, whose processing requires meticulous and time‐consuming procedures.MethodsIn an initial step, general functionality tests were carried out to verify that the equipment meets the manufacturer's specifications. A study of the accuracy of the application of correction factors to compensate for variation in detector response due to dose rate, field size and beam angle incidence has been included. Besides, to assess the ability of the array to detect inaccurately delivered treatments, systematic errors corresponding to the deviation in the position of the leaves and the accuracy of the gantry position, have been introduced. Based on these results, an estimate of sensitivity and specificity values of the device has been completed. The final step included a study applied to high gradient treatment for real cases of spatially fractionated radiotherapy, where the results of SRSMapCheck measurements have been compared with gafchromic films.ResultsGeneral commissioning tests meet the manufacturer's specifications. dose rate (DR) response variation is better than 1.5% and for DR above 50 MU/min better than 1%. The results for beam incidences are better than 1% for all gantry angles, including beam incidences parallel to the array. Field size response differences are within the range of ±1% for sizes up to 2 × 2 cm2, with a maximum value obtained of 3.5%, for 1 × 1 cm2. From the systematic error study, using a Gamma function Γ (2%, 2 mm), the detector presents a high specificity with a value greater than 90% at its lower limit, while its sensitivity has a moderate mean value of 81%. Sensitivity values increase above 86% when we apply a Gamma function Γ (2%, 1 mm) is applied. Finally, the study of actual cases comprises 17 patients, distributed into 11 lung tumors, 3 gynecological and 3 soft tissue tumors. The gafchromic film showed a lower passing rate with an average value of Γ (2%, 2 mm) = 94.1% compared to Γ (2%, 2 mm) = 98.6% reached by the measurements with the array.ConclusionsGamma function obtained with the SRSMapCheck array always presented a higher value than gafchromic film measurements, resulting in a greater number of plans considered correct. This fact, together with the sensitivity and specificity study carried out, allows us to conclude the recommendation that a restrictive metric must be established, in this way we will improve sensitivity, and therefore we will reduce the rate of incorrect plans qualified as correct. The characteristics of the equipment together with the correction factors applied, led to reliably performing acquisitions for complex treatments with multiple small targets in oblique rotational incidences. The spatial resolution of detectors allows the verification of high gradient dose plans such as those achieved in spatially fractionated radiotherapy (SFRT).

A RADIOLUMINESCENCE STUDY OF DOSE CHARACTERISTICS OF LIF:MG,TI.

A radioluminescence (RL) study of dose characteristics of tissue-equivalent LiF:Mg,Ti was carried out to determine the possible application as a real-time dosemeter. An RL measurements system based on LiF:Mg,Ti coupled with optical fiber was developed, and a blank fiber was set to remove the stem effect generated by the optical fiber due to direct radiation. A slight increase of RL sensitivity with accumulated dose and the afterglow effect due to shallow traps in LiF:Mg,Ti were observed, thus a set of algorithms was adopted to correct measured dose rate. A good linearity of dose-rate response using RL in LiF:Mg,Ti over more than four orders of magnitude (from 0.76mGy/h to 8.02Gy/h) was shown, and the deviation of calibrated dose rate is within 20%. Moreover, a satisfactory reproducibility (1.45%) of the measured dose rate after correction was represented. The results indicated that LiF:Mg,Ti might be promising for real-time dose monitoring.

Characterization of stilbene and EJ-276 scintillators coupled with a large area SiPM array for a fast neutron dose rate detector

A 1-inch stilbene and EJ-276 (plastic) organic scintillators were characterized in view of their use in a portable survey meter for fast neutron detection and dose rate measurements in radiation protection. They were coupled with a large area Silicon Photomultiplier (SiPM) array and characterized in terms of neutron/γ–ray (n/γ) discrimination capability, count rate linearity, count rate saturation effects, temperature stability and neutron detection efficiency. A Pile-Up Rejection (PUR) algorithm was developed and tested to increase their count rate linearity with increasing dose rate. Results show that the stilbene exhibits better performance compared to the plastic in terms of: Pulse Shape Discrimination (PSD) with a Figure Of Merit (FOM) of 1.5 vs. 1.1, energy resolution (15% vs 20% at 662 keV) and fast neutron efficiency (12% vs. 9% with an AmBe source). For both scintillators, the dose rate response is linear up to 1 mSv/h with a 137Cs γ-ray source. With a neutron source, the response is linear, and the FOM is almost constant for dose rates up to 1.5 mSv/h. The PUR reduces the false neutron events by one order of magnitude when the detectors are irradiated with a γ-ray source up to 10 mSv/h, and it correctly works when irradiated with an AmBe source at 1.5 mSv/h together with a 137Cs source up to 60 μSv/h. The proposed PUR algorithm is promising but needs to be tested with a higher intensity mixed n/γ field. The temperature stability of both detectors was also studied in the temperature range from −10 °C to ＋40 °C. The light yield increases by around 25% for both detectors when reducing the temperature. The variation of the neutron count rate is around 10% in the same temperature range. This work provides a complete overview of the performance of these detectors and a coherent comparison between the two types of scintillators with the same experimental setup.

Real-time dosimeter based on LiF:Mg,Cu,P and SiPM

The dose characteristics of LiF:Mg,Cu,P, using RL, weren't reported up to now. The first investigation into the use of a SiPM directly coupled to a LiF:Mg,Cu,P detector as a real-time dosimeter is presented. The signals of the dosimeter with or without a LiF:Mg,Cu,P detector were compared. The sum of the RL signals of a LiF:Mg,Cu,P detector and the signals of a SiPM itself during irradiation can be used to measure the dose rate. The reproducibility of the net count rates during irradiation at a constant dose rate of 15 mGy/h of the dosimeter was found to be within 0.25% (1 SD). This system shows an excellent linear response within the dose rate range from 0.5 mGy/h to 3 Gy/h (R2 = 0.9997). For dose rates higher than 3 Gy/h, the dose rate response is sublinear. The real-time dosimeter based on a LiF:Mg,Cu,P detector and a SiPM may have application potential for the dose rate measurement in the range of 0.5 mGy/h to 15 Gy/h, and has its own advantages over G-M counters and scintillators.

The response of low-cost photodiodes for dosimetry in electron beam processing

The response of thin diodes (SFH206k) as dosimeters has been investigated employing the beam of an electron accelerator within the dose rate range of 2–8 kGy/s and accumulated doses up to 100 kGy. These devices, operating in the short-circuit mode and under industrial irradiation conditions, deliver current signals nonlinearly dependent on the dose rate, whichever the dose history of the diodes, due to the high density of the generated electron-hole pairs herein achieved. Despite this nonlinearity, the dose rate response is stable and characterized by current signals with repeatability better than 2.0%, regardless of the accumulated dose. It is also found that the dose responses are quite linear with sensitivities slightly dependent on the accumulated dose at a constant dose rate. The decrease in the charge sensitivity, taking as reference that obtained before any radiation damage, reaches only 9% (k = 2) at 100 kGy, which is much smaller than the values reported in the literature. From this low aging and the repeatability of both dose rate and dose responses, it seems that the photodiode under investigation is a low budget alternative, good enough for routine dosimetry, provided it has been previously calibrated in the same processing facility.

Radiation mechanism of gate-controlled lateral PNP bipolar transistors in the hydrogen environment

Hydrogen plays a crucial role in realizing modern silicon devices. Molecular hydrogen may be found in processes of integrated circuit fabrication and packaging, such as wafer cleaning procedure, film depositions, high- and low-temperature anneal and die attachment by forming gas. It has been shown that hydrogen has strong effects on the total dose and dose rate response to bipolar devices. In order to study the relationship between hydrogen and radiation-induced products, we preform two experiments by using gate-lateral PNP transistors. In the first experiment, one set of devices is soaked in 100% hydrogen gas for 60 h and another set is not soaked, they are together irradiated at 5 rad(Si)/s to a total dose of 50 krad(Si). In the second experiment, devices are irradiated at 50 rad(Si)/s to 100 krad(Si), and then one group is annealed in 100% hydrogen gas and the other is annealed in the air for 40 h at the same temperature. The results show that the damage to devices which are soaked in hydrogen before irradiation is stronger than the devices that are not soaked, the anneal characteristics of devices in hydrogen gas are also changed more greatly than in the air. So the hydrogen can enhance the radiation and anneal damage to bipolar transistors. Using the gate-sweep technique, the radiation-induced products are separated and show that the hydrogen that enters into the transistor will cause the interface traps to increase and oxide trapped charge to decrease. The main reason is that the hydrogen can react with the oxide trapped charge to produce protons which can transport to the Si/SiO<sub>2</sub> interface, and then react with H-passivized bond to create interface trap. Based on the reaction mechanism presented in our work, a numerical model of enhanced low dose rate sensitivity including molecular hydrogen reaction and proton generation mechanism is established. The simulation results for the density of interface traps and oxide trapped charge show a trend consistent with the experimental data, which verifies the correctness of the damage mechanism. This research provides not only the basis of the study of damage mechanism of bipolar devices, but also the powerful support for hydrogen soaking irradiation acceleration method.

In vitro exposure of human lens epithelial cells to X-rays at varied dose-rates leads to protein-level changes relevant to cataractogenesis

Background Accumulated body of evidence shows that ionizing radiation increases the risk of cataracts. The mechanisms are not clear and the International Commission on Radiological Protection indicates a need for research into understanding the process, particularly at low doses and low dose rates of exposure. Purpose This study was designed to examine protein-level modifications in a human lens epithelial (HLE) cell-line following radiation exposures. Materials and methods HLE cell-line was subjected to X-irradiation at varied doses (0-5 Gy) and dose-rates (1.62 cGy/min and 38.2 cGy/min). Cells were collected 20 h post-exposure, lysed and proteins were clarified following fractionation by a molecular weight cut-off filtration method. Fractionated cellular proteins were enzymatically digested and subjected to mass spectrometry analysis. Results Statistically significant radiation dose-related protein changes compared to the control group were identified. Heatmap and hierarchical clustering analysis showed dose-rate dependant responses. Pathway analysis mapped the proteins to biological functions of mitochondrial dysfunction, reactive oxygen species generation, cell death, cancer, organismal injury and amyloidosis. Conclusion Overall findings suggest that ionizing radiation exposure of HLE cells by mediating dose rate-dependant oxidative stress and cell death-related mechanisms, can be relevant to cataractogenesis.

Gamma dosimetric properties of radiophotoluminescent CaSO4:Eu3+ with novel readout instrument

We report investigations carried out on radiophotoluminescence (RPL) response of Eu3+ doped CaSO4 phosphor using an in-house developed compact system for gamma dosimetry. The system comprises a sample holder to hold 200 mg phosphor powder having particle sizes 90–212 µm in the disc form (15 mm dia, 1 mm thick) and a microcontroller-based reader with Hamamatsu PMT (H10720-110) for collection of emitted luminescence. Conversion of Eu3+ to Eu2+ on gamma irradiation in phosphor samples is studied with 320 nm UVLED (FWHM 10 nm) stimulation. The performance of the system is evaluated in 100 mGy to 10,000 mGy gamma dose range and a linear response is observed. The dosimetric properties of synthesized phosphor in terms of gamma dose response, reproducibility, dose rate response, relative photon energy dependence and fading are reported.

Real-time two dimensional dosimetry using Al2O3:C and Al2O3:C,Mg films

The Investigations of this article focus on the response of Al2O3:C and Al2O3:C,Mg radioluminescence films for medical dosimetry in various MV photon beams. A dosimetry system was configured using a scientific camera, attached to the head of the linear accelerator (LINAC), facing the beam’s isocenter, where the films were placed. By using the appropriate filter and lens it is possible to measure real time two-dimensional dose-rate distributions. The key findings are that Al2O3:C,Mg films present a clear advantage compared to Al2O3:C ones, with no interference from afterglow, better film uniformity, high spatial resolution and suitability for small field beam dosimetry, while giving overall good dose-rate response in Flattening Filter (FF) and Flattening Filter Free (FFF) modes. The results show that our system can be used for planar real time dose rate assessment in medical photon dosimetry with manageable correction factors.

Characterization of a Low-Cost Plastic Fiber Array Detector for Proton Beam Dosimetry.

The Pencil Beam Scanning (PBS) technique in proton therapy uses fast magnets to scan the tumor volume rapidly. Changing the proton energy allows changing to layers in the third dimension, hence scanning the same volume several times. The PBS approach permits adapting the speed and/or current to modulate the delivered dose. We built a simple prototype that measures the dose distribution in a single step. The active detection material consists of a single layer of scintillating fibers (i.e., 1D) with an active length of 100 mm, a width of 18.25 mm, and an insignificant space (20 m) between them. A commercial CMOS-based camera detects the scintillation light. Short exposure times allow running the camera at high frame rates, thus, monitoring the beam motion. A simple image processing method extracts the dose information from each fiber of the array. The prototype would allow scaling the concept to multiple layers read out by the same camera, such that the costs do not scale with the dimensions of the fiber array. Presented here are the characteristics of the prototype, studied under two modalities: spatial resolution, linearity, and energy dependence, characterized at the Center for Proton Therapy (Paul Scherrer Institute); the dose rate response, measured at an electron accelerator (Swiss Federal Institute of Metrology).

Two-dimensional real-time quality assurance dosimetry system using μ-Al2O3:C,Mg radioluminescence films.

Background and purposeThere is a continual need for more accurate and effective dosimetric systems for quality assurance (QA) as radiotherapy evolves in complexity. The purpose of this project was to introduce a new system that minimally perturbs the main beam, while assessing its real time 2D dose-rate and field shapes. The system combined reusability, linear dose-rate response, and high spatial and time resolution in a single radiation detection technology that can be applied to surface dose estimation and QA.Materials and methodsWe developed a 2D prototype system consisting of a camera, focusing lenses and short pass filter, placed on the head of a linear accelerator, facing an Al2O3:C,Mg radioluminescent film. To check the appropriateness of multi‐leaf collimator, stability/reproducibility QA tests were prepared using the treatment planning system: including the routinely used alternating leaves, chair and pyramid checks.ResultsThe Al2O3:C,Mg film did not perturb the dose vs. depth dose curves determined with a point detector (-0.5% difference). Our results showed a dose-rate linear film response (R2 = 0.999), from 5 to 600 MU/min. Measured output factors agreed with reference data within ~1%, indicating a potential for small field dosimetry. Both chair and pyramid measured profiles were comparable with those obtained with the treatment planning system within 1%. The alternating leaves test showed an average discrepancy in the valleys of 14%.ConclusionsThe prototype demonstrated promising results. It obviated the need for corrections regarding the relative position of the camera, confirming accurate dose-rate delivery and detection of radiation fields.

Evaluating the use of Silica and PMMA Optical Fibres as Proton Beam Monitors

Recent reports have shown both poly (methyl methacrylate) (PMMA) and silica optical fibres to be ionization quenching free, making them possibly very useful dosimeters for proton beams. In this study, the response from PMMA and silica optical fibres to therapeutic proton beams are evaluated. The light output was recorded from both optical fibres, exposed to varying dose-rates of 0.5 Gy/min to 20 Gy/min from a 235 MeV isochronous cyclotron. The PMMA optical fibre was observed to have a linear dose-rate response, and a constant light emission for a constant dose-rate exposure. However, in the case of the silica optical fibres, the light output was observed to increase during a constant dose-rate exposure. If uncorrected, this accumulated dose sensitivity observed in the silica optical fibres can result in erroneous measurements.

Ultra-High-Dose-Rate FLASH Irradiation Limits Reactive Gliosis in the Brain.

Encephalic radiation therapy delivered at a conventional dose rate (CONV, 0.1-2.0 Gy/min) elicits a variety of temporally distinct damage signatures that invariably involve persistent indications of neuroinflammation. Past work has shown an involvement of both the innate and adaptive immune systems in modulating the central nervous system (CNS) radiation injury response, where elevations in astrogliosis, microgliosis and cytokine signaling define a complex pattern of normal tissue toxicities that never completely resolve. These side effects constitute a major limitation in the management of CNS malignancies in both adult and pediatric patients. The advent of a novel ultra-high dose-rate irradiation modality termed FLASH radiotherapy (FLASH-RT, instantaneous dose rates ≥106 Gy/s; 10 Gy delivered in 1-10 pulses of 1.8 µs) has been reported to minimize a range of normal tissue toxicities typically concurrent with CONV exposures, an effect that has been coined the "FLASH effect." Since the FLASH effect has now been found to significantly limit persistent inflammatory signatures in the brain, we sought to further elucidate whether changes in astrogliosis might account for the differential dose-rate response of the irradiated brain. Here we report that markers selected for activated astrogliosis and immune signaling in the brain (glial fibrillary acidic protein, GFAP; toll-like receptor 4, TLR4) are expressed at reduced levels after FLASH irradiation compared to CONV-irradiated animals. Interestingly, while FLASH-RT did not induce astrogliosis and TLR4, the expression level of complement C1q and C3 were found to be elevated in both FLASH and CONV irradiation modalities compared to the control. Although functional outcomes in the CNS remain to be cross-validated in response to the specific changes in protein expression reported, the data provide compelling evidence that distinguishes the dose-rate response of normal tissue injury in the irradiated brain.

Feasibility study on a novel tiny dosimeter using a barium titanate capacitor.

ABSTRACTIn our laboratory we have confirmed that the capacitance of barium titanate-based capacitors changes due to radiation. Since a commercially available capacitor is very small and inexpensive, it may be used as a multidimensional dose meter in which a large number of capacitor elements are arranged, or may be embedded in the body and used as an in-vivo dose meter. In this study we examined the usefulness of a dosimeter using the capacitance change of a barium titanate capacitor. As a basic property, it was confirmed that the dose linearity was good. With regard to dose rate characteristics and response to fractionated irradiation, capacitance change due to aging affects measurement accuracy, but online measurement of capacitance change immediately before irradiation can be performed to correct aging effects during irradiation. By doing this, we confirmed that the dose rate characteristics and the response to fractionated radiation are improved.

Dosimetric investigation of a new quantum dots/nanocomposite (CdTe QDs/PVK) sensor for real-time gamma radiation detection

The design of organic/inorganic polymer nanoparticles-based hybrids is promising for gamma ray sensor systems. Here, we design semiconducting nanocomposite system for efficient gamma ray harvesting system where cadmium telluride (CdTe) quantum dots act as dopant and poly(N-vinyl carbazole) (PVK) polymer acts as host. Highly crystalline 1-dodecanethiol (1-DDT) decorated CdTe quantum dots with average diameter of ~ 3 nm were synthesized and characterized with high-resolution transmission electron microscopy (HR-TEM) analysis. Nearly monodispersed CdTe/PVK nanocomposite was subsequently prepared by addition of CdTe quantum dots (QDs) in poly(N-vinyl carbazole) matrix. The photophysical interactions between polymer host and QDs have been investigated by preparing an ohmic contact detector using a conductive cell with two gold-coated walls. Gamma detecting properties of the CdTe QDs/PVK nanocomposite such as sensitivity, repeatability, and the linearity of dose rate response were assessed. Significant enhancement in photoconductivity induced by the gamma radiation in CdTe QDs/PVK nanocomposite has been demonstrated.