Evaluation of the dosimetric characteristics of a radiophotoluminescent glass dosimeter for high-energy photon and electron beams in the field of radiotherapy

We aimed to evaluate the suitability of a glass dosimeter (GD) for high-energy photon and electron beams in experimental and clinical use, especially for radiation therapy. We examined the expanded dosimetric characteristics of GDs including dose linearity up to 500 Gy, uniformity among GD lots and for individual GDs, the angular dependence, and energy dependence of 4 therapeutic x-ray qualities. In addition, we measured the dosimetric features (dose linearity, uniformity, angular dependence, and energy dependence) of the GD for electron beams of 10 different electron energy qualities. All measurements with the exception of dose linearity for photon beam were performed in a water phantom. For high-energy photon beams, dose linearity has a linear relationship for a dose ranging from 1 to 500 Gy with the coefficient of determination; R² of 0.998. The uniformity of each GD of dose measurements was within ±0.5% for four GD lots and within ±1.2% for 80 GDs. In terms of the effects of photon beam angle, lower absorbed doses of within 1.0% were observed between 60° and 105° than at 90°. The GD energy dependence of 4 photon beam energy qualities was within ±2.0%. On the other hand, the result of the dose linearity for high-energy electron beams showed well fitted regression line with the coefficient of determination; R² of 0.999 between 6 and 20 MeV. The uniformity of GDs exposed to the nominal electron energies 6, 9, 12, 16, and 20 MeV was ±1.2%. In terms of the angular dependence to electron beams, absorbed doses were within 2.0% between 60° and 105° than at 90°. In evaluation of the energy dependence of the GD at nominal electron energies between 5 and 20 MeV, we obtained responses between 1.1% and 3.5% lower than that for a cobalt-60 beam. Our results show that GDs can be used as a detector for determining doses when a high-energy photon beam is used, and that it also has considerable potential for dose measurement of high-energy electron beam.     

Segments of a commercial Ge-doped optical fiber as a thermoluminescent dosimeter in radiotherapy

Optical fibers have been proposed as dosimeters in both diagnostic and radiotherapy applications. A commercial germanium (Ge)-doped silica fiber with a 50 μm core diameter which showed good thermoluminescence (TL) properties was selected for this study. The radiation sources used were a high dose rate brachytherapy iridium-192, MV photon and MeV electron beams from a linear accelerator. The coating of the fiber was chemically removed and then annealed at 400 °C for 1 h prior to irradiation. After irradiation, the fiber was read on a Harshaw Model 3500 TLD reader. The optical fiber had one well-defined glow peak at 327 ± 2 °C at all the radiotherapy energies. The dose response was linear within the clinical relevant dose for all these energies. Reproducibility was mainly within 4–6% (one standard deviation) for high energy photons and electrons. The fiber was found to be energy independent within the MV photon energy range. At room temperature the fading up until 1 month was around 6% which was within the 6% uncertainty of the sensitivity calibration of the fiber. Re-using the fiber four times did not significantly alter the sensitivity factor. The optical fiber was found to be dose rate as well as angular independent. Central axis depth dose curves of both 10 MV photons and 12 MeV electrons using the fiber showed relatively good agreement to standard depth dose curves in water within 4%. The Ge-doped fiber is a promising TL dosimeter but improvements have to be made to reduce the reproducibility within 3% for high energy photons and electrons.     

Dosimetric evaluation of alanine-in-glass dosimeters at clinical dose levels using high-energy X-rays from a linear accelerator

This study presents the first dosimetric evaluation of the alanine-in-glass dosimeter in radiation therapy. The dosimeter is composed of a Pyrex glass tube filled with pure polycrystalline alanine. 6 MV X-ray beams from a linear accelerator were used to irradiate the dosimeter in a solid water phantom to therapy-level doses ranging from 0 to 30 Gy. An X-band electron paramagnetic resonance (EPR) spectrometer was utilized to measure the absorbed dose of the dosimeter. The doses measured by the dosimeter were compared to those from ion chamber dosimetry. It was found that the dosimeter exhibited a linear response in the dose range from 0.1 to 30 Gy. The deviation between measured and delivered doses was 0.11% over the 0.5–30 Gy range, whereas the deviation increased to about 25% at 0.1 Gy. The lowest detectable dose with an acceptable deviation limit of 5% or less was found to be 0.3 Gy. The inaccuracy in measurements at low doses can be attributed to background signals and instrument noise. The accuracy can be improved by proper selection of measurement conditions and better optimization of equipment. The findings of this study show that the alanine-in-glass dosimeter is suitable for dose measurements with acceptable accuracy down to 0.3 Gy. The dosimeter is therefore has the potential to be employed in radiotherapy applications and quality control procedures.     

Study on energy dependence of PAGAT polymer gel dosimeter evaluated using X-Ray CT

The normoxic polymer gel dosimeter evaluated with X-Ray computed tomography has emerged as a promising tool for measuring the dose delivered during radiotherapy in three dimensions. This study presents the dependence of PAGAT normoxic polymer gel sensitivity to different photon and electron energies. PAGAT polymer gel was prepared under normal atmospheric condition and irradiated with different photon energies of 1.25 MeV from Co-60 and 6 MV and 15 MV from linear accelerator and electron energies of 6, 9, 12, 15, 18 and 21 MeV from linear accelerator. Evaluation of dosimeter was performed with an X-Ray CT scanner. Images were acquired with optimum scanning protocols to reduce the signal-to-noise ratio. The averaged image was subtracted from the unirradiated polymer gel image for background. Central axis depth dose (PDD) curves obtained for each energy and polymer gel dosimeter measurements were in good agreement with diode and film measurements. Hounsfield (HU) – dose response curve for each photon and electron energy were derived from the PDD curve obtained from the gel dosimeter measurements. From the study it was clear that the HU-dose response curve was linear in the region 1–10 Gy. The dosimeter sensitivity was defined as a slope of these linear HU-dose response curves and found that the sensitivity of polymer gel decreases with increase in both photon and electron energies. This trend in dependence of PAGAT gel dosimeter sensitivity to different photon and electron energies was not dosimetrically significant. However, to evaluate the test phantom exposed with one energy using the calibration curve derived at another energy can produce clinically significant error.     

Thermoluminescence and dosimetric aspects of topaz from Yono Shigar mine in Pakistan

Topaz shows thermoluminescence (TL) on heating after exposure to ionising radiation. A study was carried out to explore the possibility to design and develop a TLD (thermoluminescence dosimeter) from locally occurring topaz. Topaz was collected from a mine in Yono Shigar valley in northern Pakistan. The samples were identified as topaz by neutron irradiation, X-ray diffraction and X-ray fluorescence. The crystals of topaz were cut into chips of dimensions compatible to the commercial TLD readers. The chips were exposed to ⁶⁰Co and/or ¹³⁷Cs gamma irradiators. The investigation features included glow curve, dose and energy responses, sensitivity, fading, reproducibility and mechanical stability. The TL glow curves revealed a stable peak at about 250 °C, whose height rose linearly with increase of irradiation dose. The TL response versus dose (calibration curve) showed the linear behaviour between 10^?2 and 10² Gy. The dose response was independent of gamma energies of ⁶⁰Co and ¹³⁷Cs. The response of topaz chips remained constant within 10% deviation from the initial value after 30 cycles of reuse. The rate of fading of topaz was very fast just after irradiation and slowed after a few days. Mechanical stability of the chips remained constant during handling in all investigation experiments. The topaz from Yono Shigar mine may be recommended as a TLD for gamma dose within 10^?2–10² Gy.     

Response of CaSO4:Dy phosphor based TLD badge system to high energy electron beams from medical linear accelerator and estimation of whole body dose and skin dose

Response of thermoluminescent dosimeter (TLD) badge based on CaSO₄:Dy phosphor to high energy electron beams from medical linear accelerators was simulated using FLUKA Monte Carlo code and experimentally verified. This study was carried out in order to determine the response of TL discs under different filter regions of the TLD badge and their ratios under different irradiation conditions in the energy range 6–20 MeV of high energy electron beams. It was found that the response of TL disc under metal filters of the TLD badge (D1) is always higher than the response of the TL discs under Polystyrene filter (D2) and open window (D3) and its response was found to decrease with increase in the energy of the electron beam. Estimation of whole body dose and skin dose including its error was carried out as an extension of the present study in case of accidental exposure of radiation worker to high energy electron beam.     

EPR of gamma-irradiated polycrystalline alanine-in-glass dosimeter

This study attempts to overcome some of the reported discrepancies in alanine-EPR reproducibility that may be related to alanine dosimeter preparation and/or EPR spectrometer settings. The dosimeters were prepared by packing pure polycrystalline $\text{<mi mathsize="small" is="true">L</mi>}\text{-}\alpha \text{-}\mathrm{alanine}$ directly as supplied by the manufacturer in glass tubes. This dosimeter production scheme avoids any possible contribution to the EPR signal from a binding material. The dosimeters were irradiated with gamma ray to low-dose ranges typical for medical therapy (0–20 Gy). Special attention has been paid to the study of minimum detectable dose, measurement repeatability and reproducibility, and post-irradiation stability. The dosimeter exhibited a linear dose response in the dose range from 0.1 to 20 Gy. These positive properties favor the polycrystalline alanine-in-glass tube as a radiation dosimeter.     

Development of a personal dosimeter badge system using sintered LiF:Mg,Cu,Na,Si TL detectors for photon fields

The badge system of personal thermoluminescence (TL) dosimeter for photon fields using LiF:Mg,Cu,Na,Si TL material, which was developed by Korea Atomic Energy Research Institute (KAERI) a few years ago, was developed by taking advantage of its dosimetric properties including energy dependencies. A badge filter system was designed by practical irradiation experiments supported by computational modeling using Monte Carlo simulation. Design properties and dosimetric characteristics such as photon energy response and angular dependence of new TL dosimeter system examined through the irradiation experiments are presented. Based on the experiments for the developed dosimeter, it is demonstrated that the deep dose response of dosimeter provided the value between 0.78 and 1.08, which is within the design limit by ISO standard. This multi-element TL dosimeter badge system allows the discrimination of the incident radiation type between photon and beta by using the ratios of the four TL detectors. Personal TL dosimeter using sintered LiF:Mg,Cu,Na,Si TL detectors has the ability to measure a personal dose equivalent H_p(d) for a wide range of photon energies.     

Focused electron beam induced deposition as a tool to create electron vortices

Focused electron beam induced deposition (FEBID) is a microscopic technique that allows geometrically controlled material deposition with very high spatial resolution. This technique was used to create a spiral aperture capable of generating electron vortex beams in a transmission electron microscope (TEM). The vortex was then fully characterized using different TEM techniques, estimating the average orbital angular momentum to be ∼0.8ℏ per electron with almost 60% of the beam ending up in the ℓ = 1 state.     

Relative efficiency of TL detectors to energetic ion beams

The relative TL efficiency of LiF:Mg, Ti and LiF:Mg, Cu, P was evaluated for several ion beams, ranging from helium to xenon ions. Irradiations were realized at the HIMAC accelerator in Chiba, Japan, partly within the ICCHIBAN intercomparison project. The covered LET range was extending from about 2 keV/μm to 1500 keV/μm.Both tested TLD types exhibited a decrease of relative response with increasing ionization density – stronger for LiF:Mg,Cu,P detectors. The relationship between efficiency and LET was found to follow unique trend lines, as nearly all data points lied within 5% around the fitted empirical functions. Values of TL efficiency measured for various batches of same type TLDs agree within a few percent. The measured relationships between relative TL efficiency and LET will be used in the analysis of data obtained from space dosimetric experiments.     

Electron beam energy monitoring using thermoluminescent dosimeters and electron back scattering

Periodic checks of megavoltage electron beam quality are a fundamental requirement in ensuring accurate radiotherapy treatment delivery. In the present work, thermoluminescent dosimeters (TLDs) positioned on either side of a lead sheet at the surface of a water equivalent phantom were used to monitor electron beam quality using the electron backscattering method. TLD100 and TLD100H were evaluated as upstream detectors and TLD200, TLD400 and TLD500 were evaluated as downstream detectors. The evaluation assessed the test sensitivity and correlation, long and short term reproducibility, dose dependence and glow curve features. A prototype of an in-air jig suitable for use in postal TLD dose audits was also developed and an initial evaluation performed. The results indicate that the TLD100-TLD200 combination provides a sensitive and reproducible method to monitor electron beam quality. The light weight and easily fabricated in-air jig was found to produce acceptable results and has the potential to be used by radiation monitoring agencies to carry out TLD postal quality assurance audits, similar to audits presently being conducted for photon beams.     

Development of new chemical dosimeter for low dose range

Accurate measurement of low dose radiation in complex systems is of utmost importance in radiation biology and related areas. Ferrous Benzoic acid Xylenol orange (FBX) system is being widely used for measurement of low dose gamma radiation because of its reproducibility and precision. However, an additional step, i.e., dissolution of benzoic acid in water at higher temperature followed by cooling at room temperature is involved for the preparation of this dosimeter. This makes it inconvenient as a ready to use dosimeter. In the present work, the organic molecule, sorbitol has been used for measurement of low doses of radiation. The advantages of using sorbitol are its ready availability and instantaneous water solubility. Owing to its dissolution at room temperature, possible errors those are involved in calculation of dose due to thermal oxidation of ferrous ions during preparation of the FBX dosimetric solution could be made insignificant in the proposed dosimeter. In the present system, sorbitol acts as radiolytic sensitizer for the oxidation of ferrous ion, and xylenol orange forms a 1:1 complex specifically with ferric ions. Thus, the analytical detection limit of ferric ions is enhanced compared to other systems. Final composition of the dosimetric solution is; 0.5 mol/m³ xylenol orange, 10 mol/m³ sorbitol and 0.2 mol/m³ ferrous ion in 50 mol/m³ sulfuric acid. Radiolytic sensitization in combination with analytical enhancement of the ferrous based system, allows us to measure radiation dose in the range of 0.05 Gy–12 Gy with ease and high reproducibility.     

Detection of sonoluminescence signals in a gel phantom in the presence of Protoporphyrin IX conjugated to gold nanoparticles

The particles in a liquid decrease the ultrasonic intensity threshold required for cavitation onset. In this study, a new nanoconjugate composed of Protoporphyrin IX and gold nanoparticles (Au–PpIX) was used as a nucleation site for cavitation. The nonradiative relaxation time of Protoporphyrin IX in the presence of gold nanoparticles is longer than the similar time without gold nanoparticles. The acoustic cavitation activity was investigated via recording of the integrated sonoluminescence signal in the wavelength range of 220–700 nm in a gel phantom by a cooled charge coupled device (CCD) at different intensities of 1 MHz ultrasound. In order to confirm these results, a chemical dosimetric method was utilized, too. The recorded sonoluminescence signal in the gel phantom containing Au–PpIX was higher than the other phantoms. These records have been confirmed by the chemical dosimetric data. Therefore, we anticipate that a new nanoconjugate composed of Protoporphyrin IX and gold nanoparticles can act as an efficient sonoluminescence agent and could be introduced as a novel sonosensitizer for sonodynamic therapy.     

Dual frequency cavitation event sensor with iodide dosimeter

The inertial cavitation activity depends on the sonication parameters. The purpose of this work is development of dual frequency inertial cavitation meter for therapeutic applications of ultrasound waves. In this study, the chemical effects of sonication parameters in dual frequency sonication (40 kHz and 1 MHz) were investigated in the progressive wave mode using iodide dosimetry. For this purpose, efficacy of different exposure parameters such as intensity, sonication duration, sonication mode, duty factor and net ultrasound energy on the inertial cavitation activity have been studied. To quantify cavitational effects, the KI dosimeter solution was sonicated and its absorbance at a wavelength of 350 nm was measured. The absorbance values in continuous sonication mode was significantly higher than the absorbance corresponding to the pulsed mode having duty factors of 20–80% (p < 0.05). Among different combination modes (1 MHz_100% + 40 kHz_100%, 1 MHz_100% + 40 kHz_80%, 1 MHz_80% + 40 kHz_100%, 1 MHz_80% + 40 kHz_80%), the continuous mode for dual frequency sonication is more effective than other combinations (p < 0.05). The absorbance for this combined dual frequency mode was about 1.8 times higher than that obtained from the algebraic summation of single frequency sonications. It is believed that the optimization of dual frequency sonication parameters at low-level intensity (<3 W/cm²) by optically assisted cavitation event sensor can be useful for ultrasonic treatments.     

Developing a mailed phantom to implement a local QA program in Egypt radiotherapy centers

In this work, a simple method that differs from the IAEA/WHO Thermoluminescent dosimeters (TLD) postal quality assurance (QA) program is developed. A small perspex; polymethyl methacrylate (PMMA), phantom measured 50?mm?×?50?mm?×?50?mm is constructed to be used for absorbed dose verification of high-energy photon beams in some major radiotherapy centers in Egypt. The phantom weighted only 140.7?g with two buildup covers weighted 14.8 and 43.19?g for the Cobalt-60 and the 6-MV X-ray beams, respectively. This phantom is aimed for use in the future’s external audit/QA services in Egypt for the first time. TLD-700 chips are used for testing and investigating a convenient and national dosimetry QA program. Although the used methodology is comparable to previously introduced but new system; it has smaller size, less weight, and different more available material. Comparison with the previous similar designs is introduced. Theoretical calculations were done by the commercial Eclipse treatment planning system, implementing the pencil beam convolution algorithm to verify the accuracy of the experimental calculation of the dose conversion factor of water to the perspex phantom. The new constructed small phantom and methodology was applied in 10 participating radiotherapy centers. The absorbed dose was verified under the reference conditions for both ⁶⁰Co and 6-MV high-energy photon beams. The checked beams were within the 5% limit except for four photon beams. There was an agreement of 0.2% between our experimental data and those previously published confirming the validity of the applied method in verifying radiotherapy absorbed dose.     

Optically stimulated luminescence from BeO ceramics: An LM-OSL study

Optically Stimulated Luminescence (OSL) signals of BeO ceramics were investigated using continuous wave (CW) OSL and Linearly Modulated (LM) OSL. It was found that both curves can be approximated using a linear combination of two first-order components. Experiments on the measurement temperature dependence have shown that these two components have nearly the same thermal quenching energies around 0.57 eV. Dependences of the OSL signal on preheat temperature and radiation dose were also examined. Thermal annealing experiments have shown that OSL signals originate from traps which are unstable near 340 °C, thus proving the suitability of the signals for dosimetric purposes. Dose response was found to be linear and a minimum detectable dose of ～10 μGy was found.     

Comparison of hydroxyl radical formation in aqueous solutions at different ultrasound frequencies and powers using the salicylic acid dosimeter

Ultrasonic frequencies of 20 kHz, 382 kHz, 584 kHz, 862 kHz (and 998 kHz) have been compared with regard to energy output and hydroxyl radical formation utilising the salicylic acid dosimeter. The 862 kHz frequency inputs 6 times the number of Watts into water, as measured by calorimetry, with the other frequencies having roughly the same value under very similar conditions. A plausible explanation involving acoustic fountain formation is proposed although enhanced coupling between this frequency and water cannot be discounted. Using the salicylic acid dosimeter and inputting virtually the same Wattages it is established that 862 kHz is around 10% more efficient at generating hydroxyl radicals than the 382 kHz but both of these are far more effective than the other frequencies. Also, it is found that as temperature increases to 42 °C then the total dihydroxybenzoic acid (Total DHBA) produced is virtually identical for 382 kHz and 862 kHz, though 582 kHz is substantially lower, when the power levels are set at approximately 9 W for all systems. An equivalent power level of 9 W could not be obtained for the 998 kHz transducer so a direct comparison could not be made in this instance. These results have implications for the optimum frequencies chosen for both Advanced Oxidation Processes (AOPs) and organic synthesis augmented by ultrasound.     

Characterization of GaN dosimetry for 6 MV photon beam in clinical conditions

We characterized a recently proposed implantable GaN-based dosimeter in clinical conditions, for its application in external radiotherapy according to ESTRO (European Society for Radiotherapy & Oncology) practical guidelines. Our studies were carried out using a 6 MV photon beam with the dosimeter under test in a water tank or a PMMA phantom. They were focused on evaluating short term and long term reproducibility of measurements, and assessing the effects of parameters such as field size, source-skin distance, use of wedge filter, beam incidence, dose rate, accumulated dose, GaN-induced dose perturbation, air cavities and temperature. The estimated repeatability and reproducibility are better than 0.5% and 2% at 1σ respectively. There are no significant effects of the parameters under our studies, apart from field size and temperature. The field-size dependence is due to over-compensation of the GaN response method of the dosimeter, the resulting errors remain lower than 5% for field sizes up to 10 × 10 cm². The temperature dependence mainly results from the GaN luminescence properties, and causes the GaN response to decrease steadily when increasing temperature, with a sensitivity of −1.4%/°C. The observed quasi-linear temperature dependence may facilitate the correction to improve the accuracy of measurements.     

Assessment of undesirable dose to eye-melanoma patients after proton radiotherapy

Radiotherapy with a proton beam of initial energy 55–80 MeV is presently the clinically recommended therapy for some cases of intraocular melanoma such as large melanomas or tumours adjacent to critical organs. Evaluation and optimization of radiation doses outside the treatment volume may contribute to reducing undesirable side-effects and decreasing the risk of occurrence of secondary cancers, particularly for paediatric patients. In this work the undesired doses to organs were assessed basing on Monte Carlo calculation of secondary radiation transport and on results of measurements of neutron and γ-ray doses at the proton therapy facility of the Institute of Nuclear Physics at Kraków. Dosimetry was performed using a He-3-based FHT 762 neutron monitor (Wendi II), a FH40G proportional counter (for γ-rays), and MTS-7 (LiF:Mg,Ti) thermoluminescence detectors (TLDs). Organ doses were calculated in the ADAM anthropomorphic phantom using the MCNPX Monte Carlo transport code and partly verified, for γ-ray doses, with TLD measurements in the RANDO Anderson anthropomorphic phantom. The effective dose due to undesired radiation, including exposure from scattered radiation during the entire process of proton radiotherapy and patient positioning using X-rays, does not exceed 1 mSv.     

Characterization of a scintillating fiber-optic dosimeter for photon beam therapy

Abstact  A scintillating fiber-optic dosimeter has many advantages such as real-time readout, high-resolution measurement, water-equivalence and no corrections for temperature, pressure and humidity. Organic scintillator which has water or tissue equivalent characteristics is very important to measure absorbed dose, dose rate and dose distributions exactly without any corrections and due to its small size, the sensitive volume enables accurate dose measurements in regions of high dose gradients with high spatial resolution. In this study, a scintillating fiber-optic dosimeter with an organic scintillator is fabricated to measure high-energy photon beam from a clinical linear accelerator. And we have measured linear responses of a fiber-optic dosimeter according to dose rates and monitor units of a clinical linear accelerator. Also, a percent depth dose curve for 6MV photon beam with different field sizes are obtained.