Precision Of Dose Measurements Research Articles

3D dose distribution measurement using 2D imaging from NaCl optical crystals

In radiotherapy practice, 1D and 2D dosimeters are used for dose verification prior to patient treatment. Along with high accuracy and precision of dose measurements that these dosimeters provide, acquisition of dose deposition data in three dimensions requires extrapolation of measured data. Development of a 3D dosimeter would provide continuous information of dose distribution in matter. In this work, NaCl 3D crystal has shown that radiation deposition can be imaged using blue laser stimulation in two dimensions. It was further shown that the intensity of collected signal has near – linear dose dependence, however complete signal readout is required, to compensate for gradual signal collection at different depths along the profile of the stimulating laser beam, due to attenuation of the beam within the crystal. A method to extend dose measurement to three dimensions using imaging is proposed.

The analysis of the measurement uncertainty with application of small detectors made of Gafchromic EBT films for the range of doses typical for in vivo dosimetry in teleradiotherapy

IntroductionThe required overall uncertainty in dose delivery in modern radiotherapy is 3.5% of a prescribed dose (one standard deviation). In vivo dosimetry is the simple method in dose delivery control. In this work we present our results concerning the precision of dose measurement with Gafchromic EBT films used within the dose range measured in the in vivo dosimetry of photon external beam radiation therapy. Materials and methodsThe rectangular pieces of Gafchromic EBT films of 1 cm × 2 cm were prepared. They were prepared from three different films from two batches. For each film four sets of samples consisting of 18 pieces were made. Each set of films was exposed perpendicularly to 6 MV photon beams at several dose levels from 2 cGy to 190 cGy. The net optical density was read with the flatbed document scanner Epson Expression 10000 XL and the ImageJ software. The calibration curves for each set of Gafchromic EBT samples were obtained. The mathematical formulae describing the calibration curve was fitted to the measurements results. Four different calibration procedures were analyzed based on one or four sets of samples and with or without use of image filtration (median filter). Two sources of uncertainty were analyzed separately: the calibration curve measurements, and the precision of formulae fitting. ResultsFor the protocol described in this paper, the overall dose measurement uncertainty of less than 2% (one standard deviation) for doses of about 25 cGy and higher was found for calibration procedure based on four sets of film samples with image filtration, and less than 3% for calibration procedure based on one set of film samples with image filtration. For two films from the same batch almost identical calibration curves were obtained. It allows to use one calibration curve for all films from the same batch. There were larger differences for films from two different batches. ConclusionsThe Gafchromic EBT films have sufficient accuracy for dose measurements above 20 cGy and may be an interesting alternative for the semiconductor or thermoluminescent detectors as an in vivo dosimeter. Contrary to these detectors Gafchromic EBT films are transparent for radiation.

Artifacts suppression in optical CT for gel dosimeters by iterative reconstruction

Optical CT has been considered as an important and promising readout method for 3D gel dosimetry. However, tomographic image qualities are often corrupted by artifacts such as streaks and rings, which are induced by projection discontinuities and magnified by FBP reconstruction. These artifacts will surely deteriorate the accuracy and precision of dose measurement. In this paper, we performed a preliminary study on our in-house optical CT scanner using an iterative algorithm instead of the commonly used FBP for image reconstruction. Comparative analysis of the results validates the proposed method in artifacts suppression and image quality improvement when the convergent process is properly controlled.

The effect of sample/planchet geometry and temperature resolution on the reproducibility of glow curve shapes and precision of dose measurement in LiF-TLD-100 thermoluminescent dosimetry

The effect of accurate positioning of TLD-100 samples in the center of the reader planchet on precision and kinetic parameters was investigated. Significant improvement in precision is obtained by careful positioning of the sample in the center of the planchet, by as much as 40%, 20% and 30% using different methods of glow curve analysis to estimate the intensity of the TL signal.

The analysis of readout values according to reading methods: Glass dosimeter reader

The accuracy and precision of dose measurement using a glass dosimeter (GD) depend on appropriate and stable operation of the GD reader. The aim of this study is to evaluate the stability of readout values of the reader and to recommend effective use of reading methods for reducing the uncertainty in dosimetric performance through the investigation of characteristics of a GD-based reader system. The examined glass dosimetry system consists of silver-activated metaphosphate GD element and a fully automatic readout system. GD elements were calibrated and exposed using a 60Co teletherapy unit (Theratron 780, AECL, Kanata, Canada). The reproducibility of repeated measurements results show that the readout value is 0.4% lower at fifth measurement, 0.9% lower at tenth measurement, and 1.3% lower at the twentieth measurement, compared to the reference value. The resulting readout values of the GD elements according to the loading positions were at minimum 0.5% lower, and at maximum, 3.1% higher, with an average of 2.0% higher values compared to the reference readout value in the first position. The interface effect for dose due to the loading number of GD elements was evaluated to be 1.015, 1.022, and 1.035 times higher in the average dose values for the loading of five GD elements, ten GD elements, and twenty GD elements than the average readout value at the first position, respectively. As a result, in order to get an accurate and precise dose measurement by the GD reader, if repeated readings are performed, measured values should be corrected according to the number of repeated readings, and the loading of GD elements in the magazine should constantly be kept in the same position. Moreover, the number of GD elements loading on the magazine should be decided by considering either accurate and precise dose measurements or numerous relative dose measurements.

SU‐GG‐T‐349: Generalized Formalism and Optimization of the Calibration Sequence of Plastic Scintillation Detectors

Purpose: Effects of Cerenkov light on plastic scintillation detectors (PSD) can be successfully corrected, but an inadequate calibration might result in erroneous measurements. The purpose of this work is to establish a general calibration formalism and to perform a systematic study of calibration sequences to optimize PSD performances. Methods and Materials: A general mathematical formalism has been developed with no a priori assumption on the physical characteristics of the detector system. This formalism was used in simulations of realistic PSD systems (i.e. similar to PSDs published in the literature) for over 1000 different calibration sequences. The accuracy and precision of dose measurements with PSD calibrated with each sequence were then analyzed and compared. We also studied the propagation of errors in the whole measurement chain. Results: Optimized calibration sequence can improve precision by a factor of 3 when dose readings are performed with more than 15 cm of optical fibers irradiated. In addition, a 3‐point calibration sequence prevents systematic error in calibration factors measured in the presence of large (>0.5%) statistical noise. Our study also outlined several “calibration pitfalls” that should be avoided: Calibration points that are too similar will unduly deteriorate measurement precision (e.g. calibration with fields of 10 and 30 cm will increase the measurement standard deviation by 1.5 compared to calibrations with fields of 3 and 30 cm); Small dosimetric errors made at calibration time can result in large systematic measurement error with PSDs. A 1% dose error on one of the calibration measurements can result in a 4% to 10% accuracy error with the PSD when more than 15 cm of clear optical fiber is irradiated. Conclusions: We developed a new PSD calibration formalism. After optimization of the calibration sequence of PSDs we showed improvements in both precision and accuracy of current PSD systems.

The thermoluminescent properties of lithium triborate (LiB3O5) activated by aluminium

In this paper, the thermoluminescence (TL) dosimetric characteristics of Al-doped LiB3O5 compounds are presented. The powder samples were prepared by the solid-state reaction method and the formation of the compounds were confirmed by an X-ray diffraction study. The TL studies of undoped and Al-doped LiB3O5 samples showed similar glow curve structures. They have three TL glow peaks at about 60, 130 and 200°C after heating at a constant heating rate of 1°C/s. Their comparative TL studies indicated that 5wt% Al-doped LiB3O5 compound was approximately 240 times more sensitive than undoped compound. The TL emission spectra of Al-doped LiB3O5 showed a maximum band at around 520nm. The main dosimetric characteristics, which are namely the TL dose response, TL sensitivity, fading, minimum detectable dose, reproducibility, precision of dose measurement and annealing procedure, indicated that Al-doped LiB3O5 sample, can be used in dosimetric applications. The trap parameters namely order of kinetics (b), activation energy (E) and frequency factor (s) associated with the glow peaks in beta irradiated undoped and Al-doped LiB3O5 samples were obtained by glow curve deconvolution (GCD) program.

Q-BAND EPR BIODOSIMETRY IN TOOTH ENAMEL MICROSAMPLES: FEASIBILITY TEST AND COMPARISON WITH X-BAND

A comparative study of electron paramagnetic resonance dosimetry in Q- and X-bands has shown that Q-band is able to provide accurate measurements of radiation doses even below 0.5 Gy with tooth enamel samples as small as 2 mg. The optimal amount of tooth enamel for dose measurements in Q-band was found to be 4 mg. This is less than 1% of the total amount of tooth enamel in one molar tooth. Such a small amount of tooth enamel can be harmlessly obtained in an emergency requiring after-the-fact radiation dose measurement. The other important advantage of Q-band is full resolution of the radiation-induced EPR signal from the native, background signal. This separation makes dose response measurements much easier in comparison to conventional X-band measurements in which these overlapping signals necessitate special methods for doses below 0.5 Gy. The main disadvantages of Q-band measurements are a higher level of noise and lower spectral reproducibility than in X-band. The effect of these negative factors on the precision of dose measurements in Q-band could probably be reduced by improvement of sample fixation in the resonance cavity and better optimization of signal filtration to reduce high-frequency noise.

Thermoluminescence of undoped and Ce-doped BaB 4O 7

In this paper, the TL dosimetric characteristics of undoped and Ce-doped BaB 4O 7 compounds are reported. The polycrystalline powder samples were prepared by a melting method and the formation of the compounds were confirmed by an X-ray diffraction study. The TSL studies of undoped BaB 4O 7 sample show a prominent glow peak at 195 °C and three small peaks at 117, 255 and 365 °C whereas Ce-doped sample show three prominent TL glow peaks at 195, 250, 331 °C and two small peaks at around 90 and 135 °C when heated at a constant heating rate of 1 °C/s. Comparative TSL studies of these two compounds show that the Ce-doped BaB 4O 7 compound is approximately five times more sensitive than undoped compound. The TL emission spectra of Ce-doped showed a maxima at 360 nm for all measurements during TL measurements which is attributed to the characteristic emission from 5d to 4f transitions of Ce 3+ ion. The main dosimetric characteristics, which are namely the TL dose response, TL sensitivity, fading, minimum detectable dose, reproducibility, precision of dose measurement and annealing procedure, were shown that Ce-doped BaB 4O 7 sample could be used in dosimetric applications. The trap parameters namely order of kinetics ( b), activation energy ( E) and frequency factor ( s) associated with the glow peaks in β-irradiated undoped and Ce-doped barium borate samples were also obtained by computer glow curve deconvolution (CGCD) method.

Dosimetric performance requirements for the routine dose assessment of external radiation.

Dosimetric performance requirements must take the following into consideration: general radiation protection requirements established by the International Commission on Radiological Protection (ICRP), workplace conditions prevailing during (routine) work, and technical requirements set by international or national bodies. For performance tests the general requirements on the precision of dose measurements can be represented by the 'trumpet curves'. For photon radiation several measurements of the workplace conditions are reported. The main conclusions drawn from these measurements are the following: the photon energy range from 20 keV to 2 MeV, or even 7 MeV, is of importance for individual monitoring. The range of directions of radiation incidence on the dosemeter is very large, nearly the frontal hemisphere or even rotating, and almost all spectra are broad with respect to energy. In view of the great variety of workplace conditions, the scope of most of the technical requirements is not sufficiently great. No technical requirement is at present fully in accordance with the general principles of an uncertainty analysis.

Dosimetric characteristics of tissue equivalent thermoluminescent solid TL detectors based on lithium borate

This paper presents the main dosimetric characteristics of newly prepared, complete tissue-equivalent thermoluminescent dosimeters Li 2B 4O 7:Cu,In, and Li 2B 4O 7:Cu, in the form of sintered pellets. The dosimetric characteristics of lithium borate thermoluminescent dosimeters examined in this study, include glow-curve shapes, TL sensitivity, photon dose response, minimum detectable dose, relative photon energy response, fading, reproducibility, precision of dose measurements and annealing procedure.