Sensitive Dosimeter Research Articles

Brachytherapy dosimeter with silicon photomultipliers

In-vivo and in-situ measurement of the radiation dose administered during brachytherapy faces several technical challenges, requiring a very compact, tissue-equivalent, linear and highly sensitive dosimeter, particularly in low-dose rate brachytherapy procedures, which use radioactive seeds with low energy and low dose deposition rate. In this work we present a scintillating optical fiber dosimeter composed of a flexible sensitive probe and a dedicated electronic readout system based on silicon photomultiplier photodetection, capable of operating both in pulse and current modes. The performance of the scintillating fiber optic dosimeter was evaluated in low energy regimes, using an X-ray tube operating at voltages of 40–50kV and currents below 1mA, to assess minimum dose response of the scintillating fiber. The dosimeter shows a linear response with dose and is capable of detecting mGy dose variations like an ionization chamber. Besides fulfilling all the requirements for a dosimeter in brachytherapy, the high sensitivity of this device makes it a suitable candidate for application in low-dose rate brachytherapy. According to Peralta and Rego [1], the BCF-10 and BCF-60 scintillating optical fibers used in dosimetry exhibit high variations in their sensitivity for photon beams in the 25–100kVp energy range. Energy linearity for energies below 50keV needs to be further investigated, using monochromatic X-ray photons.

Preparation and characterization of novel Sulfosalicylic acid-Ferrous-PVA hydrogel as a 3D dosimeter

A colorless transparent hydrogel SSA-Ferrous-PVA was prepared as a 3D dosimeter using 5-sulfosalicylic acid. Under serial doses of irradiation by a 60Co source, dosimeter turned into pink with serial color densities. The resulting color densities were characterized by a UV–vis spectrophotometer at the fixed wavelength of 505 nm. Various concentrations of 5-sulfosalicylic acid and ferrous ammonium sulfate were tested by linear relevant fitting for optimal hydrogel production conditions. The effects of various formulations were evaluated on the stability and sensitivity of dosimeters. The slopes of diffusion curves were measured and used to evaluate the diffusion rates of irradiated dosimeters. Results indicated that a careful doping with 5-sulfosalicylic acid produced a hydrogel with a colorless transparent background and an optimal dosimeter with a low diffusion rate, good stability, and great linearity of dose response.

Enhancement in dose sensitivity of polymer gel dosimeters composed of radiation-crosslinked gel matrix and less toxic monomers

Polymer gel dosimeters based on radiation-crosslinked hydroxypropyl cellulose gel were prepared, which comprised 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol #400 dimethacrylate (9G) as less toxic monomers and tetrakis (hydroxymethyl) phosphonium chloride (THPC) as an antioxidant. The dosimeters exposed to 60Co γ-rays became cloudy at only 1 Gy. The irradiated dosimeters were optically analyzed by using a UV- vis spectrophotometer to evaluate dose response. Absorbance of the dosimeters linearly increased in the dose range from 0 to 10 Gy, in which dose sensitivity increased with increasing 9G concentration. The dose sensitivity of the dosimeters with 2 wt% HEMA and 3 wt% 9G was also enhanced by increment in THPC.

Characterization of a PN3 personal neutron dosimeter based on (n,α) reaction

This study describes a new methodology for characterizing the sensitivity of personal neutron dose-equivalent dosimeters consisting of a PN3 (trade name of the CR-39 type) nuclear track detector coupled with a natural boron converter BN1 (20% 10B, 80% 11B) and enriched boron converter 10B (99% 10B). Both dosimeters (converter+detector) were mounted in an ISO water-filled phantom and were simultaneously irradiated in terms of personal dose equivalent Hp(10) ranging between 1 and 4mSv under standard neutron radiation fields generated by (252Cf+D2O) and (252Cf+D2O)/Cd) sources. After irradiation, the latent tracks produced by alpha particles were revealed through a chemical solution. The optimum etching conditions (6.25N, 70°C for 7h) used, were performed for an initial in-depth study. The response of the dosimeter was given by the ratio of the average track density obtained by subtracting the tracks due to the 252Cf+D2O and (252Cf+D2O)/Cd sources to the dose equivalent. The calibration factor was found to be 2826±17 tracks.cm−2.mSv−1. The sensitivity of the dosimeter was observed to be increased significantly using a converter enriched in 10B (99% 10B).

Luminescence Properties of CaF2 Nanostructure Activated by Different Elements

Nanostructures of calcium fluoride (CaF2) doped with Eu, Tb, Dy, Cu, and Ag were synthesized by the coprecipitation method and studied for their thermoluminescence (TL) and photoluminescence (PL) properties. The PL emission spectrum of pure CaF2 nanostructure has a broad band in the 370–550 nm range. Similar spectra were observed in case of doped samples, beside extra bands related to these impurities. The maximum PL intensity was observed in Eu doped sample. The TL results of Eu, Cu, Ag, and Tb doped samples show weak glow peaks below 125°C, whereas Dy doped one is found to be highly sensitive with a prominent peak at 165°C. This sample was further exposed to a wide range of gamma rays exposures from 137Cs source. The response curve is linear in the 100 Gy‐10 kGy range. It is also observed that the particle size of CaF2 nanostructure was significantly reduced by increasing Dy concentration. These results showed that Dy is a proper activator in the host of CaF2 nanostructure, providing a highly sensitive dosimeter in a wide range of exposures and also plays a role as a controlling agent for particle size growth.

The Opposite Effects of the Heating Rate on the TSL Sensitivity of Ge-doped Fiber and TLD500 Dosimeters

One of the main criteria for choosing a thermoluminescent dosimeter (TLD) is its sensitivity to the radiations under investigation. Increasing the heating rate during readout often appears necessary to reduce the time between the measurements and the dose evaluation, especially in routine dosimetry. However, doing this degrades the radiation sensitivity of common dosimeters, as illustrated in this work for the TLD500 dosimeter. It is shown that the germanium-doped optical fiber (GDF) is not only more sensitive to radiation than these COTS dosimeters but, unlike them, its sensitivity is enhanced when the heating rate increases. The physical origin of this rare effect of sensitivity enhancement is probably due to the temperature dependence of the recombination rate by which the detrapped electrons upon stimulation are transferred to the luminescent centers. The effect of light exposure on the dose information stored in both GDF and a commercial TLD is also reported.

Spatial dosimetric sensitivity of contouring uncertainties in gynecological 3D-based brachytherapy

Background and purposeThis study aims to analyze subsections of the target volume that are sensitive to delineation uncertainties with respect to underdosage (spatial dosimetric uncertainty) in MRI-based brachytherapy of cervical cancer. Material and methodsA methodology was developed to simulate delineation uncertainties by shifting an angular segment of the contour perpendicular to the original HR-CTV. For shifts of 3, 6 and 9mm resulting D90 and D98 were calculated for the modified contour. The sensitivity of the dose plan to the locally introduced error was estimated by linear regression of D90 or D98 against the magnitude of the shift. The methodology was employed on 20 patients treated with tandem ring brachytherapy. ResultsTopographic maps resulting from the dosimetric sensitivity analysis showed both large spatial variations and substantial inter-patient variations. For all plans included the spatial sensitivity in D90 ranged from 0.0 to −1.6%/mm, correspondingly sensitivity in D98 ranged from 0 to −4.6%/mm. A significantly increased dosimetric sensitivity was found in anterior direction and the cranial part of the tumor (p<0.05). ConclusionsThe developed methodology identifies specific tumor regions and patients with increased risk of underdosage from delineation uncertainties in brachytherapy of cervical cancer.

Optical properties of some modified plant compound after 662 keV gamma radiation

Plant-isolated compounds, Osthol [7-methoxy-8-(3-methylbut-2-enyl) coumarin], were subjected to modification in the isopentenyl side chain to get an aldehyde of 2-methyl-4 (7-methoxy-2-oxo-2H-chromen-8-yl)-but-2-en-1-al. This modified compound was exposed to γ-radiation produced by 137Cs source at room temperature. Pre- and post-irradiation study was carried out by ultraviolet–visible spectroscopy. The compound shows a sharp absorption peak at 322 nm. This observed absorption band decreases with irradiation up to a certain dose and then increases with a further increase in the radiation dose. This compound exhibits almost a linear response up to 7 Gy. From the optical data analysis, this compound follows indirect allowed transition and the optical gap was found around 3.58 eV. The systematic decrease in the band gap was found with an increase in the radiation dose. Urbach energy is also found to decrease with radiation. This parameter gives a clear indication of the defects and free radical created in the system after irradiation. The present features shown by this compound may be exploited as sensitive dosimeter in 0–7 Gy γ-radiation environment.

Dosimetric Evaluation of Polymer Gel Dosimeter Using Saccharide in Clinical Radiation Therapy System

Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools and tissue equivalent phantom developed to date. In this study, changes in the characteristics of MAGIC gel from the perspective of tissue equivalence and dose sensitivity were examined. In this paper, the dose responses of the MAGIC gel with various concentrations and type of saccharide are examined to clarify the roles of mono- and di-saccharide in the polymerization process. Then we focused on the tissue equivalence and dose sensitivity of MAGIC gel dosimeters.

Correlation between ferrous ammonium sulfate concentration, sensitivity and stability of Fricke gel dosimeters exposed to clinical X-ray beams

This work describes the characterization of various Fricke-Agarose-Xylenol gels (FXG) dosimeters using NMR relaxometry and MRI analysis. Using X-rays from a clinical linear accelerator (LINAC), the gels were irradiated in the dose range from 0Gy to 20Gy. The photon sensitivity of the FXGs was measured in terms of NMR relaxation rates; its dependence on radiation dose was determined as a function of ferrous ammonium sulfate contents (from 0.5mM to 5mM). Furthermore, the stability of the NMR signal was monitored over several days after irradiation. These measurements were aided by Magnetic Resonance Imaging (MRI) scans which allowed three-dimensional (3D) dose mapping. In order to maximize the MRI response, a systematic study was performed to optimize acquisition sequences and parameters. In particular, we analyzed the dependence of MRI signal on the repetition time (TR) and on the inversion time (TI) using inversion recovery sequences. The results are reported and discussed from the point of view of the dosimeter use in clinical radiotherapy. This work highlights that the optimization of additive content inside gel matrix is fundamental for optimizing photon sensitivity of these detectors.

Investigation of a pulsed current annealing method in reusing MOSFET dosimeters for in vivo IMRT dosimetry.

To explore the feasibility of pulsed current annealing in reusing metal oxide semiconductor field-effect transistor (MOSFET) dosimeters for in vivo intensity modulated radiation therapy (IMRT) dosimetry. Several MOSFETs were irradiated at d(max) using a 6 MV x-ray beam with 5 V on the gate and annealed with zero bias at room temperature. The percentage recovery of threshold voltage shift during multiple irradiation-annealing cycles was evaluated. Key dosimetry characteristics of the annealed MOSFET such as the dosimeter's sensitivity, reproducibility, dose linearity, and linearity of response within the dynamic range were investigated. The initial results of using the annealed MOSFETs for IMRT dosimetry practice were also presented. More than 95% of threshold voltage shift can be recovered after 24-pulse current continuous annealing in 16 min. The mean sensitivity degradation was found to be 1.28%, ranging from 1.17% to 1.52%, during multiple annealing procedures. Other important characteristics of the annealed MOSFET remained nearly consistent before and after annealing. Our results showed there was no statistically significant difference between the annealed MOSFETs and their control samples in absolute dose measurements for IMRT QA (p = 0.99). The MOSFET measurements agreed with the ion chamber results on an average of 0.16% ± 0.64%. Pulsed current annealing provides a practical option for reusing MOSFETs to extend their operational lifetime. The current annealing circuit can be integrated into the reader, making the annealing procedure fully automatic.

A comment on the article on EPR in silver-alanine nanocomposites for radiation detection by Guidelli et al. in Nanoscale, 4, 2012.

This comment refers to possibility of increasing the radiation sensitivity of alanine EPR dosimeters by introduction of silver nanoparticles.

Dosimetry study of diagnostic X-ray using doped iodide normoxic polymer gels

In radiotherapy, polymer gel dosimeters are used for three-dimensional (3D) dose distribution. However, the doses are within the Gy range. In this study, we attempted to develop a low-dose 3D dosimeter within the mGy range for diagnostic radiology. The effect of the iodinated compound was used as a dose enhancement sensitizer to enhance the dose sensitivity of normoxic polymer gel dosimeters. This study aims to use N-isopropylacrylamide(NIPAM)-based and methacrylic acid (MAGAT)-based gels to evaluate the potential dose enhancement sensitizer, as well as to compare two gels that may be suitable for measuring diagnostic radiation doses. The suitable formulation of NIPAM gel [5% (w/w) gelatin, 5% (w/w) NIPAM, 3% (w/w) N,N′-methylenebisacrylamide (BIS), 5mM tetrakis (hydroxymethyl) phosphonium chloride (THPC), and 87% (w/w) deionized distilled water] and MAGAT gel (4% MAA, 9% gelatin, 87% deionized water, and 10mM THPC) were used and loaded with clinical iodinated contrast medium agent (Iobitridol, Xenetix® 350). Irradiation was conducted using X-ray computed tomography. The irradiation doses ranged from 0mGy to 80mGy. Optical computed tomography was the employed gel measurement system. The results indicate that the iodinated contrast agent yields a quantifiable dose enhancement ratio. The dose enhancement ratios of NIPAM and MAGAT gels are 3.35±0.6 and 1.36±0.3, respectively. The developed NIPAM gel in this study could be suitable for measuring diagnostic radiation doses.

Bolus-dependent dosimetric effect of positioning errors for tangential scalp radiotherapy with helical tomotherapy

The dosimetric effect of errors in patient position is studied on-phantom as a function of simulated bolus thickness to assess the need for bolus utilization in scalp radiotherapy with tomotherapy. A treatment plan is generated on a cylindrical phantom, mimicking a radiotherapy technique for the scalp utilizing primarily tangential beamlets. A planning target volume with embedded scalplike clinical target volumes (CTVs) is planned to a uniform dose of 200cGy. Translational errors in phantom position are introduced in 1-mm increments and dose is recomputed from the original sinogram. For each error the maximum dose, minimum dose, clinical target dose homogeneity index (HI), and dose-volume histogram (DVH) are presented for simulated bolus thicknesses from 0 to 10mm. Baseline HI values for all bolus thicknesses were in the 5.5 to 7.0 range, increasing to a maximum of 18.0 to 30.5 for the largest positioning errors when 0 to 2mm of bolus is used. Utilizing 5mm of bolus resulted in a maximum HI value of 9.5 for the largest positioning errors. Using 0 to 2mm of bolus resulted in minimum and maximum dose values of 85% to 94% and 118% to 125% of the prescription dose, respectively. When using 5mm of bolus these values were 98.5% and 109.5%. DVHs showed minimal changes in CTV dose coverage when using 5mm of bolus, even for the largest positioning errors. CTV dose homogeneity becomes increasingly sensitive to errors in patient position as bolus thickness decreases when treating the scalp with primarily tangential beamlets. Performing a radial expansion of the scalp CTV into 5mm of bolus material minimizes dosimetric sensitivity to errors in patient position as large as 5mm and is therefore recommended.

Thermoluminescent dosimetry properties of double doped calcium tetraborate (CaB4O7:Cu–Mn) nanophosphor exposed to gamma radiation

This study reports the dosimeteric properties of double Cu–Mn doped calcium tetraborate nanophosphor prepared by co-precipitation technique. The structure and the morphology of the synthesized nanocrystals were characterized by X-ray diffraction and transmission electron microscope. The presented XRD patterns showed the monoclinic structure and transmission electron microscopy revealed the formation of spherical shape nanoparticles with an average particle size of 8 nm. The results demonstrated that the synthesized calcium borate nanophosphor has the highest dosimetric sensitivity at combined concentration of 2% and 1%, copper and manganese molar ratio, respectively. TL glow curve of this material showed two well resolved peaks located at around 124 and 256 °C. The most striking dosimeteric feature of this nanomaterial is the linearity response, which has a long range of 0.05–3000 Gy for both temperature peaks.

Comparison of the influence of inorganic salts on the NMR dose sensitivity of polyacrylamide-based gel dosimeter

On the NMR dose sensitivities of polyacrylamide-based gel dosimeters irradiated by X-ray, the additive effect of various inorganic salts (electrolytes) is investigated. Among the various combination of cations (Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Zn2+ and Al3+) and anions (Cl−, NO−3 and SO2-4), MgCl2 is shown to be the most effective sensitizer. In the result, it is suggested that the extent of the increase of the dose sensitivity may correlate to the hydration power of cations rather than anions. Contrary to the dose sensitivity enhancement, the depression of melting point caused by the additives is also pointed out.

Dosimetric characteristics of N-vinylpyrrolidone based polymer gels: utilization depending on dose range

In this study, two types of normoxic N-vinylpyrrolidone based polymer gel, VIPET1v and VIPET2v, were presented. VIPET2v had the double amount of monomer compared to the VIPET1v. The influence of this difference in the dosimetric characteristics of the polymer gel dosimeters was investigated. The doubling in N-vinylpyrrolidone concentration increased the dose sensitivity in the linear dose range region and improved the dose resolution at 95% confidence level for lower doses (D<10Gy). Unfortunately, this increase in concentration reduced the dose range response. VIPET1v was sensitive in the dose range of 2 to 60 Gy, while VIPET2v was sensitive in the dose range of 1 to 30 Gy. Moreover, both gels showed a linear R2-dose response for one month post-irradiation time period. During this time, variations in dose sensitivity and offset values of both dosimeters were observed. Finally, the dose resolution temporal stability was studied and was eventually improved by doubling the N-vinylpyrrolidone concentration.

Influence of preparation and calibration method of PAGAT dosimeter on TSE MR readout results

In this study PAGAT dosimeter evaluation by TSE sequence was tested. PAGAT dosimeter preparation procedure was modified to increase the dosimeter sensitivity. Because THPC reacts with gelatin, adding THPC to monomer solution prior to dissolved gelatine helps exploit THPC as an antioxidant. Turbo spin echo sequence enables to evaluate gel dosimeter with 3D equidistant resolution in a reasonable scanning time. Glass walls of the phantom cause problems both by computing inaccuracies and MR imaging artefacts. The inner dosimeter volume is not affected by these inaccuracies and should be used for radiotherapy plan verification.

SU-E-T-158: Evaluation of the Sensitivities of Patient Specific IMRT QA Dosimeters

Purpose: To analyze the sensitivity of patient‐specific IMRT QA devices to detecting plan failures when compared to multiple ion chamber measurements. Methods: Four methods of IMRT QA were chosen: film (Kodak EDR2) and ion chamber (Wellhofer cc04) in an I'mRT body phantom, MapCheck2 (Sun Nuclear) with fields delivered AP, and MapCheck2 in the MapPhan phantom with rotational fields. Additionally, an in‐house designed multiple ion chamber phantom with an insert containing 5 ion chambers (Exradin A1SL 0.057cc) that can rotate to eight positions was used as a gold standard. Twenty plans previously failing film and ion chamber IMRT QA at our institution and five passing plans were delivered to all devices. The plans' performance on the in‐house phantom sorted them into true fails and passes. The sensitivity to detect true failures was assessed across devices with acceptance criteria of 3%/3mm and 90% of pixels passing for planar, and 3% dose difference for point measurements. Additionally, specificity was analyzed. Results: The sensitivities among all devices were less than 0.70 (poor), indicating a deficiency in identifying plans that failed versus multiple ion chamber measurements. The specificities were generally high. The AP‐delivered MapCheck has the lowest sensitivity (0.27), while the rotationally‐delivered Mapcheck MapPhan had the lowest specificity (0.70) due the directional dependence of diodes. Film was the most sensitive (0.60) dosimeter under investigation, while the single ion chamber had the highest specificity (1.00). Conclusion: The different sampling methods of each device lead to a difference in the ability to detect true failures as determined by multiple ion chamber readings. The overall low sensitivities among all devices indicates that failing plans are passing, leading to a potential lack of error detection in patients' IMRT plans. This work was supported by Public Health Service grants CA010953, CA081647, and CA21661 awarded by the National Cancer Institute, United States Department of Health and Human Services.

COMS eye plaque brachytherapy dosimetric sensitivity to source photon energy and seed design

This study explores the influence of source photon energy on eye plaque brachytherapy dose distributions for a 16mm COMS plaque filled with 103Pd, 125I, or 131Cs sources or monoenergetic photon emissions ranging from 12keV to 100keV. Dose distributions were similarly created for all permutations of three common brachytherapy seed designs. Within this range, sources with average energy ≤22keV may reduce dose to the opposite eye wall by more than a factor of 2 while maintaining tolerable proximal sclera doses when prescribing to depths of 9mm or less. Current commercially-available brachytherapy sources can exhibit up to 15% relative dosimetric sensitivity to seed design at regions within the eye.