Technical Note: Robust individual thermoluminescence dosimeter tracking using optical fingerprinting.

Midplane dose determination during total body irradiation using in vivo dosimetry

Cone beam computed tomography, CBCT, is a kind of CT scanner producing conical divergingX-rays, in which a large area of a two-dimensional detector is irradiated in each rotation. Different investigations have been performed on dosimetry of dental CBCT. As there is no special protocol for dental CBCT, CT scan protocols are used for dosimetry. The purpose of this study is measurement of dose to head and neck organs in two CBCT systems, i.e. Planmeca 3D Mid (PM) and NewTom VGi (NT), using thermoluminescence dosimetry and Rando phantom. The thermoluminescent dosimetry (TLD)-100 chips were put at the position of different organs of the head and neck. Two TLD-100 chips were inserted at each position, the dose values were measured for several different field sizes, i.e. 8 × 8, 12 × 8 and 15 × 15 cm2 for NewTom, and 10 × 10 and 20 × 17 cm2 for Planmeca systems. According to the results, the average effective dose in PM is much more than the NT system in the same field size, because of the greater mAs values. For routine imaging protocols used for NT, the effective dose values are 70, 73 and 121 µSv for 8 × 8, 12 × 8and 15 × 15 cm2 field sizes, respectively. In PM, the effective dose in 10 × 10 cm2 and 17 × 20 cm2 is 259 and 341 µSv, respectively.

The objective of this paper was to measure the peripheral dose (PD) with diode and thermoluminescence dosimeter (TLD) for intensity modulated radiotherapy (IMRT) with linear accelerator (conventional LINAC), and tomotherapy (novel LINAC). Ten patients each were selected from Trilogy dual-energy and from Hi-Art II tomotherapy. Two diodes were kept at 20 and 25 cm from treatment field edge. TLDs (LiF:MgTi) were also kept at same distance. TLDs were also kept at 5, 10, and 15 cm from field edge. The TLDs were read with REXON reader. The readings at the respective distance were recorded for both diode and TLD. The PD was estimated by taking the ratio of measured dose at the particular distance to the prescription dose. PD was then compared with diode and TLD for LINAC and tomotherapy. Mean PD for LINAC with TLD and diode was 2.52 cGy (SD 0.69), 2.07 cGy (SD 0.88) at 20 cm, respectively, while at 25 cm, it was 1.94 cGy (SD 0.58) and 1.5 cGy (SD 0.75), respectively. Mean PD for tomotherapy with TLD and diode was 1.681 cGy SD 0.53) and 1.58 (SD 0.44) at 20 cm, respectively. The PD was 1.24 cGy (SD 0.42) and 1.088 cGy (SD 0.35) at 25 cm, respectively, for tomotherapy. Overall, PD from tomotherapy was found lower than LINAC by the factor of 1.2-1.5. PD measurement is essential to find out the potential of secondary cancer. PD for both (conventional LINAC) and novel LINACs (tomotherapy) were measured and compared with each other. The comparison of the values for PD presented in this work and those published in the literature is difficult because of the different experimental conditions. The diode and TLD readings were reproducible and both the detector readings were comparable.

Purpose: A novel method to measure organ dose distributions in a phantom of heterogeneous tissue composition was established using radiochromic XRQA‐2 films. Film response accuracy was validated using thermoluminescent dosimeters (TLDs). Method and Materials: Film response accuracy and sensitivity in CT exposure geometry were verified by comparing TLD responses between two CTDI head phantoms. The phantoms were placed end‐to‐end to allow for a uniform scatter environment. TLDs and films were placed between cross‐sectional slabs of a 5‐yr old anthropomorphic phantom's thorax and abdomen regions. Software was written for dosimeter comparison within a complex anthropomorphic phantom. Film accuracy within the anthropomorphic phantom was measured by comparing TLD results within the lung, liver, and kidney organs. Results: Film and TLD dose response differences were measured for CTDI phantom, 45% (SD ± 2%), and for the anthropomorphic phantom in the lung, 28% (SD ± 8%), and liver/kidneys, 15% (SD ± 4%). Due to consistent response differences in low and high organ dose, a tissue specific correction was applied to the film organ responses. Corrected film response agreed to better than 3% (SD ± 2%), for CTDI scans, and 3% (SD ± 3%) for lungs, 5% (SD ± 3%) for liver, and 4% (SD ± 3%) for kidneys. Film measured a heterogeneous dose distribution within the organ volumes; the extent of which was not measured with the TLDs. XRQA film demonstrated an advantage over the TLD method by discovering a 15% greater maximum dose to lung in a region unmeasured by TLDs. Conclusion: XRQA films demonstrated lower sensitivity to absorbed dose measurements due to geometric inefficiencies of measuring dose from a beam situated end‐on to the film. Corrected film responses demonstrated equivalent measurement accuracy as TLD detectors with the added advantage of measuring high‐resolution dose distributions throughout an organ volume.

Dose conversion factors for absorbed dose in a mobile phone to absorbed dose in critical organs in an anthropomorphic phantom for emergency dosimetry applications: OSL and TL experimental results, and Monte Carlo simulations

Estimation of effective radiation dose for physicians and staff members in contrast angiocardiography

A postal dose intercomparison program based on the thermo-luminescence dosimeter (TLD) was carried in order to investigate and reduce uncertainties involved in the measurement of absorbed dose, and to improve the accuracy of dose measurement at different radiotherapy centers in Bangladesh. The intercomparison program was organized by the Secondary Standard Dosimetry Laboratory (SSDL) with the assistance of the IAEA/WHO postal dose intercomparison network. A set of three TLDs (encapsulated LiF powder) including a control was sent to the participating radiotherapy centers for irradiation with 2 Gy of absorbed dose to water. The measurements were made for 60Co and megavolts X-ray beam. Thirteen beams in total were checked. Deviation of ±5% between stated and evaluated dose was considered to be acceptable for 60Co and 6MV X-ray beam. The result of 60Co beam of two centers exceeds the acceptance limit. The maximum deviation was -8.6% with an uncertainty of 1.8% i.e., the ratio of intercomparison dose to locally measured dose was 1.09. We discussed the immediate and corrective action to minimize the discrepancies. For ten 60Co beam measurements, a mean valued of the ratio of intercomparison dose to locally stated dose was 0.988 with a standard deviation of 0.031. The importance of a proper ongoing quality assurance program is essential in maintaining the consistency and the uniformity of absorbed dose measurement for the precision dose delivery to the patient.

QA measurement of gamma-ray dose and neutron activation using TLD-400 for BNCT beam

Thermoluminescent dosimeters (TLDs), particularly CaF/sub 2/:Mn, are often used as photon dosimeters in mixed (n//spl gamma/) field environments. In these mixed field environments, it is desirable to separate the photon response of a dosimeter from the neutron response. For passive dosimeters that measure an integral response, such as TLDs, the separation of the two components must be performed by postexperiment analysis because the TLD reading system cannot distinguish between photon- and neutron-produced response. Using a model of an aluminum-equilibrated TLD-400 (CaF/sub 2/:Mn) chip, a systematic effort has been made to analytically determine the various components that contribute to the neutron response of a TLD reading. The calculations were performed for five measured reactor neutron spectra and one theoretical thermal neutron spectrum. The five measured reactor spectra all have experimental values for aluminum-equilibrated TLD-400 chips. Calculations were used to determine the percentage of the total TLD response produced by neutron interactions in the TLD and aluminum equilibrator. These calculations will aid the Sandia National Laboratories-Radiation Metrology Laboratory (SNL-RML) in the interpretation of the uncertainty for TLD dosimetry measurements in the mixed field environments produced by SNL reactor facilities.

Background: Calibration of Thermo Luminescent Dosimetry (TLD) in eye lens dosimeter requires a standard phantom. The use of anthropomorphic phantoms in calibration needs evaluation.Objective: This study aimed to analyze the angular response of the TLD on the fabricated 3D anthropomorphic head phantom and Computerized Imaging Reference Systems (CIRS)- Computed Tomography (CT) dose phantom as a standard phantom irradiated with Cs-137 and to compare the absorbed dose and linear attenuation for both phantoms. Hp(3) analysis, conversion coefficient (hpK(3)), and calibration factor (CF) are also investigated.Material and Methods: In this experimental study, the fabricated 3D printed anthropomorphic head phantom was analyzed using polylactic acid (PLA) with the skull and then filled with the artificial brain and cerebrospinal fluid (CSF) as a test phantom. TLD-700H and TLD Reader Harshaw 6600 plus were used to analyze the angular response of Cs-137 radiation and to determine the absorbed dose and linear attenuation coefficient of test and standard phantoms.Results: The effect of the angle of radiation source towards TLD reading at the anthropomorphic head phantom has a similar value to the standard phantom with a calibration factor ranging from 0.82 to 1. The absorbed dose measurement and the linear attenuation coefficient of the anthropomorphic head phantom with the standard phantom have different values of 2.52 and 3.78%, respectively.Conclusion: The fabricated 3D printed anthropomorphic head phantom has good potential as an alternative to standard phantoms for TLD calibration in eye lens dosimeter.

An optical fingerprinting solution with a switchable backlight is demonstrated for liquid crystal displays (LCDs). In fingerprinting mode, the collimated infrared light is applied to improve the signal-noise ratio (SNR) between the valley and ridge of the fingerprint. Compared with the conventional backlight, the proposed structure can effectively improve the SNR. Furthermore, the fingerprinting mode and the display mode may work at the same time without interference because of the different wavelengths and light paths. It shows the great potential application of LCD-based optical fingerprints.

The evolution of high-NA projection optics design and manufacturing tolerances has been remarkable in recent years. Nevertheless, different instances of identical scanner models can still exhibit unique optical fingerprints which can impart subtle patterning differences for a given mask exposed at nominally identical conditions on different scanners. In some cases, a product can be shown statistically to yield lower when a certain layer is exposed on a particular scanner. Thus it is common to have a certain subset of the total population of tools allowed for certain critical levels, such as gate. Since a single mask is typically shared between the multiple allowed scanners, the optical proximity correction model which is employed in the generation of that mask must represent the average fingerprint of those tools. In practice, CD data may be collected from multiple tools, but more often a single tool is somehow identified as the "golden" tool for the purpose of calibrating the OPC model. Once the mask is generated, however, its printing behavior on multiple scanners can readily be simulated using tool-specific optical models. Such models can be easily generated based upon known optical fingerprint data, such as measured illumination source maps, Jones pupil or Zernike aberration files. This paper investigates the use of tool-specific optical models to elucidate the intersection of design and process variability, which will manifest differently on each scanner, depending upon subtle details of the scanner fingerprint.

Intercomparison of Environmental Gamma doses Measured with A NaI (Tl) Survey Meter and Thermoluminescent Dosimeters (TLDs) in the Poonch Division of Azad Kashmir, Pakistan

We have developed a method for obtaining the cumulated activities in organs from radionuclides, which are injected into the patient in nuclear medicine procedures, by external exposure measurement with thermoluminescent dosimeters (TLDs) which are attached to the patient's body surface close to source organs to obtain information on body-surface doses. As the surface dose is connected to the cumulated activities in source organs through radiation transmission in the human body which can be estimated with the aid of a mathematical phantom, the organ cumulated activities can be obtained by the inverse transform method. The accuracy of this method was investigated by using a water phantom in which several gamma-ray volume sources of known activity were placed to simulate source organs. We then estimated by external measurements the organ cumulated activities and absorbed doses in subjects to whom the radiopharmaceuticals -labelled Doxepin, -labelled YM09151-2 and -labelled Benzotropin were administered in clinical nuclear medicine procedures. The cumulated activities in the brain obtained with TLDs for Doxepin and YM09151-2 are and respectively, which are compared with the respective values of and with direct PET (positron emission tomography) measurements. The agreement between the two methods is within a factor of two. The effective doses of Doxepin, YM09151-2 and Benzotropin are determined as , and respectively with the TLD method. This method has great advantages, in that cumulated activities in several organs can be obtained easily with a single procedure, and the measurements of body surface doses are performed simultaneously with the nuclear medicine procedure, as TLDs are too small to interfere with other medical measurements.

To evaluate the radiation dose, image quality, and Cobb angle measurements obtained with a digital scanning method of scoliosis radiography. Multiple images were reconstructed into one image at a workstation. A low-dose alternative was to use digital pulsed fluoroscopy. Dose measurements were performed with thermoluminescent dosimeters in an Alderson phantom. At the same time, kerma area-product values were recorded. A Monte Carlo dose calculation also was performed. Image quality was evaluated with a contrast-detail phantom and visual grading system. Angle measurements were evaluated with an angle phantom and measurements obtained on patient images. The effective radiation dose was 0.087 mSv for screen-film imaging, 0.16 mSv for digital exposure imaging, and 0.017 mSv for digital fluoroscopy; the corresponding kerma area-product values were 0.43, 0.87, and 0.097 Gy. cm(2), respectively. The image quality of the digital exposure and screen-film images was about equal at visual grading, whereas fluoroscopy had lower image quality. The angle phantom had lower angle values with digital fluoroscopy, although the difference in measured angles was less than 0.5 degrees. The patient images showed no difference in angles. The described digital scanning method has acceptable image quality and adequate accuracy in angle measurements. The radiation dose required for digital exposure imaging is higher than that required for screen-film imaging, but that required for digital fluoroscopy is much lower.