A practical EPR dosimetry system for routine use in radiotherapy: uncertainty analysis of lithium formate dosimeters at the therapeutic dose level.

In electron paramagnetic resonance (EPR) dosimetry, solid dosimeter materials such as alanine (AL) or, more recently, lithium formate monohydrate (LFM) are typically used. These materials offer high potential for applications in radiotherapy based on their favorable dosimetric properties. Nevertheless, EPR dosimetry is not widespread in the clinics. This work presents an uncertainty analysis of EPR dosimetry in the dose range from 1 to 70 Gy using a compact spectrometer and applying a practical procedure being suitable for routine use in radiotherapy. The performances of self-pressed LFM pellets and commercial AL pellets are compared side by side. All pellets had a diameter of 4 mm and a height of 2 mm (AL) or 4 mm (LFM). The mean pellet mass was 35.81 mg and 73.81 mg for AL and LFM, respectively. Before irradiation, the pellets were stored for at least 8 weeks at 34 ± 2% relative humidity. For irradiation, the pellets were put inside an airtight capsule. In total, 25 pellets per material were examined. The pellets were irradiated at a temperature of 25 ± 2.5 (2σ) °C to doses of either 1, 5, 20, 50 or 70 Gy (five pellets per dose value and material) by a clinical 6 MV photon beam. Measurement uncertainties were obtained from five independent readouts per pellet within five weeks following irradiation using a benchtop EPR spectrometer. The measurement time of a single readout was restricted to 10 min per pellet. Dose values were derived from EPR signal amplitudes using a specifically developed spectral fitting procedure. Signal fading characteristics were analyzed and taken into account during evaluation. The relative dose uncertainties (1σ) for a single readout at doses ≥ 5 Gy are below 2.8% (AL) and 1.1% (LFM) but increase to 12.3% (AL) and 2.6% (LFM) at 1 Gy. By averaging five independent readouts, the uncertainties at 1 Gy decrease to 2.6% (AL) and 0.8% (LFM). In terms of dose uncertainty, the LFM pellets are superior to the commercial AL pellets owing to their narrower EPR spectrum and approximately doubled mass resulting in higher EPR signal intensities. In case of the LFM pellets, the EPR dosimetry system shows a high level of precision (< 3%) down to 1 Gy being preferable for applications in radiotherapy. The uncertainties can be further decreased by averaging multiple dose values from independent readouts.

Eye Lens Dosimetry in Interventional Radiology: Assessment With Dedicated Hp(3) Dosimeters.

PURPOSE: To quantify eye lens dose in interventional radiology and assess whether neck dosimeter is a good surrogate to evaluate eye lens dosimetry. METHODS: Radiation exposure was prospectively measured in 9 interventional radiologists between May and October 2017. Standard Hp(0,07) thermoluminescent dosimeters (TLDs) were worn at the neck outside the lead apron, and 2 dedicated eye lens Hp(3) TLDs were placed just above the eyes, one midline and another at the outer edge of the left eye. Correlations between eye lens and neck TLD doses were assessed with Pearson coefficient, and linear regression was used to predict eye lens dose from neck TLD values. RESULTS: Eye lens dose without eye protection was 0.18 ± 0.11 (mean ± standard deviation; 0.08-0.41) mSv per workday and 35.3 ± 6.6 mSv (16.3-82.9) annually (200 workdays/year). Five (56%) radiologists exceeded the 20 mSv annual eye lens dose limit. Eye lens doses from left and central TLDs were 12.46 ± 3.02 and 9.29 ± 3.38 mSv, respectively (P = .027). Mean eye lens (left and central) and neck TLD doses were 10.87 ± 2.67 and 16.56 ± 5.67 mSv, respectively (P = .008). Pearson correlation coefficient between both eye lens TLD and between mean eye lens TLD and neck TLD doses were 0.91 and 0.92, respectively. Average of eye lens dose was 0.0179 + (0.5971 × neck dose). CONCLUSION: Full-time interventional radiologists are likely to suffer from deterministic radiation effects to the eye lens, especially on the left side. Neck TLD significantly overestimates eye lens dose. However, eye lens doses are highly correlated with neck doses and may be predicted from the neck TLD values.

Characterization of novel 3D printed plastic scintillation dosimeters.

We propose a new methodology for the fabrication and evaluation of scintillating detector elements using a consumer grade fusion deposition modeling (FDM) 3D printer. In this study we performed a comprehensive investigation into both the effects of the 3D printing process on the scintillation light output of 3D printed plastic scintillation dosimeters (PSDs) and their associated dosimetric properties. Fabrication properties including print variability, layer thickness, anisotropy and extrusion temperature were assessed for 1 cm3 printed samples. We then examined the stability, dose linearity, dose rate proportionality, energy dependence and reproducibility of the 3D printed PSDs compared to benchmarks set by commercially available products. Experimental results indicate that the shape of the emission spectrum of the 3D printed PSDs do not show significant spectral differences when compared to the emission spectrum of the commercial sample. However, the magnitude of scintillation light output was found to be strongly dependent on the parameters of the fabrication process. Dosimetric testing indicates that the 3D printed PSDs share many desirable properties with current commercially available PSDs such as dose linearity, dose rate independence, energy independence in the MV range, repeatability, and stability. These results demonstrate that not only does 3D printing offer a new avenue for the production and manufacturing of PSDs but also allows for further investigation into the application of 3D printing in dosimetry. Such investigations could include options for 3D printed, patient-specific scintillating dosimeters that may be used as standalone dosimeters or incorporated into existing 3D printed patient devices (e.g. bolus or immobilization) used during the delivery of radiation therapy.

Characterization of novel polydiacetylene gel dosimeter for radiotherapy.

Polymer gel dosimeters are instrumental for clinical and research applications in radiotherapy. These dosimeters possess the unique ability to record dose distribution in three dimensions. A Polymer gel dosimeter is composed of organic molecules in a gel matrix, which upon irradiation polymerize to form a conjugated polymer with optical absorbance proportional to the irradiated dose. Other required characteristics of a radiotherapy clinical dosimeter are soft-tissue equivalency, linear dose-response in a range of clinical treatments, and long term stability for the duration of the analysis. The dosimeter presented in this paper is based on diacetylene bearing fatty acid aggregates embedded in a soft-tissue equivalent gel matrix, Phytagel™, which upon irradiation polymerize to form a blue phase polydiacetylene with a strong optical absorption. Initial characterization showed that PDA-gel irradiated with 160 kV x-ray responded linearly to the irradiated dose, and the calculated diffusion coefficient is [Formula: see text] what is very low. It was also found that the percentage depth dose (PDD) curve of the PDA-gel in a 4 × 4 cm2 field, irradiated with 6 MV x-rays, was with good agreement with the literature. PDA-gel has the potential to detect absorbed dose in a range of clinical radiological irradiation regimes.

ESTIMATION OF Hp(3) TO THE EYE LENS OF INTERVENTIONAL RADIOLOGISTS-RELATION BETWEEN THE EYE LENS DOSE AND RADIOLOGIST'S HEIGHT.

The aim of the study was to estimate occupational radiation dose to the eye lens of radiologists and the dose reduction ratio of lead glasses during interventional radiology. Three interventional radiologists monitored Hp(3) using small-type optically stimulated luminescence dosemeters attached to the left inside and outside of the lead glasses with 0.07-mmPb [Hp(3)eye]. Hp(10) and Hp(0.07) were monitored, respectively, by attaching the personal dosemeter to the lead neck collar above the lead apron. The median Hp(3)eye with lead glasses and the median dose reduction ratio of lead glasses for the three radiologists were 8.02 mSv/y and 57.7%, respectively. The median Hp(3)eye without lead glasses [Hp(3)eye-w/o] for the three radiologists was 18.6 mSv/y, but Hp(3)eye-w/o for one of the radiologists was 24.1 mSv/y. Monitoring occupational radiation dose to the eye lens is important because interventional radiologists are at risk of exceeding the new dose limit.

An injectable dosimeter for small animal irradiations.

Accuracy and precision in dosimetry is crucial in studies involving animal models. Small animal dosimetry, in particular for protracted exposures to non uniform radiation fields is particularly challanging. We have developed a novel in vivo dosimeter based on glass encapsulated TLD rods. These encapsulated rods can be injected into mice and used for validating doses to an individual mouse in a protracted irradiation scenario where the mouse is free to move in an inhomogenous radiation field. Data from 30 irradiated mice shows a reliable dose reconstruction within 10% of the nominal delivered dose.

PERFORMANCE OF THE INSTADOSETM DOSEMETER FOR INTERVENTIONAL RADIOLOGY AND CARDIOLOGY APPLICATION.

The aim of this article was to verify the performance of the Mirion InstadoseTM dosemeter under clinical conditions and to compare its response in typical X-ray fields used during interventional and cardiology procedures with the TLD-100, usually used for radiation dosimetry. It was also objective of this study to verify the feasibility of using the InstadoseTM dosemeter response at the chest level for estimation of occupational eye lens dose in cardiology and interventional radiology. Initially the response of the dosemeter was tested using continuous X-ray beams and the results showed that the Instadose dosemeter present a satisfactory behavior of the most important dosimetric properties based on the tests as described in the IEC 62387 standard. The measurements performed in clinical conditions showed that the InstadoseTM dosemeter response was comparable to that of TL dosemeters used in interventional radiology and cardiology procedures and there is a correlation between the eye lens doses and the chest doses measured with the InstadoseTM. Based on the results obtained, we recommend the use of the InstadoseTM dosemeter for purposes of occupational whole-body monitoring of medical staff in interventional radiology and cardiology procedures.

A systematic review of clinical applications of polymer gel dosimeters in radiotherapy.

Radiotherapy has rapidly improved because of the use of new equipment and techniques. Hence, the appeal for a feasible and accurate three-dimensional (3D) dosimetry system has increased. In this regard, gel dosimetry systems are accurate 3D dosimeters with high resolution. This systematic review evaluates the clinical applications of polymer gel dosimeters in radiotherapy. To find the clinical applications of polymer gel dosimeters in radiotherapy, a full systematic literature search was performed on the basis of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines in electronic databases up to January 31, 2017, with use of search-related terms in the titles and abstracts of articles. A total of 765 articles were screened in accordance with our inclusion and exclusion criteria. Eventually, 53 articles were included in the study. The findings show that most clinical applications of polymer gel dosimeters relate to external radiotherapy. Most of the gel dosimeters studied have acceptable dose accuracy as a 3D dosimeter with high resolution. It is difficult to judge which is the best polymer gel dosimeter to use in a clinical setting, because each gel dosimeter has advantages and limitations. For example, methacrylic acid-based gel dosimeters have high dose sensitivity and low toxicity, while their dose response is beam energy dependent; in contrast, N-isopropylacrylamide gel dosimeters have low dose resolution, but their sensitivity is lower and they are relatively toxic.

Essential considerations for accurate evaluation of photoneutron contamination in Radiotherapy.

Nowadays, high-energy X-rays produced by medical linear accelerators (LINACs) are widely used in many Radiation Therapy (RT) centers. High-energy photons (> 8 MeV) produce undesired neutrons in the LINAC head which raise concerns about unwanted neutron dose to the patients and RT personnel. Regarding the significance of radiation protection in RT, it is important to evaluate photoneutron contamination inside the RT room. Unfortunately, neutron dosimeters used for this purpose have limitations that can under the best conditions cause to > 10% uncertainty. In addition to this uncertainty, the present Monte Carlo (MC) study introduces another uncertainty in measurements (nearly up to 20%) when neutron ambient dose equivalent (Hn*(10)) is measured at the patient table or inside the maze and the change in neutron energy is ignored. This type of uncertainty can even reach 35% if Hn*(10) is measured by dosimeters covered by a layer of 10B as converter. So, in these cases, neglecting the change in neutron energy can threaten the credibility of measured data and one should attend to this energy change in order to reduce measurement uncertainty to the possible minimum. This study also discusses the change in neutron spectra and Hn*(10) at the patient table caused by removing a typical RT room from MC simulations. Under such conditions, neutron mean energy (En) overestimated by 0.2-0.4 MeV at the patient table. Neutron fluence (φn) at the isocenter (IC) was underestimated by 23-54% for different field sizes that caused Hn*(10) to be miscalculated up to 24%. This finding informs researchers that for accurate evaluation of Hn*(10) at the patient table, simulating the RT room is an effective parameter in MC studies.

Medical Professional Radiation Dosimeter Usage: Reasons for Noncompliance.

The purpose of this study was to assess the attitudes of occupationally exposed employees at a large teaching hospital about wearing their assigned personal radiation dosimeters. A 16-question multiple-answer survey was used to report the reasons why medical professionals may not wear their dosimetry during procedures involving ionizing radiation. In all, 302 employees responded to the survey. The majority of respondents who reported always or almost always wearing their dosimeters do so because they consider themselves well informed concerning the importance of personal dosimetry measurement and appreciate the importance of federal and state regulations. For respondents who reported not always wearing their dosimeters, the most commonly stated reason was the inconvenience of remembering to bring and wear their dosimeters when working in multiple locations, for which a potential solution would be to provide dosimeters to each affected wearer in each location where they work.

Perioperative Measurement of Radiation Exposure to Radiation-Sensitive Organs of Patients Undergoing Lumbar Surgeries Using a Thermoluminescent Dosimeter.

OBJECTIVE: To introduce a method of accurately measuring the equivalent dose received by radiation-sensitive organs using the thermoluminescent dosimeter (TLD) and to provide reference values for future studies associated with radiation protection in patients undergoing lumbar spine surgeries. METHODS: After careful selection and preparation, TLD chips were used to obtain measurements from the eyes, thyroid glands, breasts, and gonads of 20 patients undergoing lumbar spine surgeries. The results were obtained via air kerma conversion-related calculations. RESULTS: The overall radiation exposures absorbed perioperatively by the eyes, thyroid glands, right breasts, left breasts, right ovaries, left ovaries, and testes were 0.41 ± 0.13, 1.43 ± 0.45, 6.95 ± 3.63, 9.50 ± 6.14, 29.86 ± 28.62, 23.47 ± 22.10, and 5.41 ± 1.86 mSv, respectively. A single computed tomography (CT) scan contributed to more than 75% of the overall dose received regardless of the position used. CONCLUSIONS: Patients received significantly higher radiation doses from CT scans than from regular digital radiograph examinations. These radiation doses were concentrated in the regional area of scanning. Our results indicate the necessity and benefits of radiation protection measures, especially for the organs researched herein, when patients undergoing lumbar surgeries require radiographic diagnostic examinations.

Radiation exposure to the surgeon during minimally invasive spine procedures is directly estimated by patient dose.

PURPOSE: Radiation exposure is a necessary component of minimally invasive spine procedures to augment limited visualization of anatomy. The surgeon's exposure to ionizing radiation is not easily recognizable without a digital dosimeter-something few surgeons have access to. The aim of this study was to identify an easy alternative method that uses the available radiation dose data from the C-arm to accurately predict physician exposure. METHODS: The senior surgeon wore a digital dosimeter during all minimally invasive spine fusion procedures performed over a 12-month period. Patient demographics, procedure information, and radiation exposure throughout the procedure were recorded. RESULTS: Fifty-five minimally invasive spine fusions utilizing 330 percutaneous screws were included. Average radiation dose was 0.46 Rad/screw to the patient. Average radiation exposure to the surgeon was 1.06 ± 0.71 µSv/screw, with a strong positive correlation (r = 0.77) to patient dose. The coefficient of determination (r2) was 0.5928, meaning almost two-thirds of the variability in radiation exposure to the surgeon is explained by radiation exposure to the patient. CONCLUSIONS: Intra-operative radiation exposure to the patient, which is easily identifiable as a continuously updated fluoroscopic monitor, is a reliable predictor of radiation exposure to the surgeon during percutaneous screw placement in minimally invasive spinal fusion surgery and therefore can provide an estimate of exposure without the use of a dosimeter. With this, a surgeon can better understand the magnitude of their exposure on a case-by-case basis rather than on a quarterly basis, or more likely, not at all. These slides can be retrieved under Electronic Supplementary Material.

Type testing of a locally made LiF:Mg,Ti + PTFE TLD for its use as a personal dosimeter.

Our research group has developed a thermoluminescence dosimeter (TLD) based on pellets of LiF:Mg,Ti mixed with polytetrafluoroethylene (LiF:Mg,Ti +PTFE). This TLD can be used as a personal dosimeter. Extensive type testing, carried out with reference to the International Electrotechnical Commission (IEC) Standard, were performed for the purpose of accepting the LiF:Mg,Ti+PTFE as a personal TL dosimeter. Tests performed include repeatability, batch homogeneity, linearity, detection threshold, and light sensitivity. Results showed that locally made LiF:Mg,Ti+PTFE TLDs met all the standard requirements.

Feasibility of dose enhancement assessment: Preliminary results by means of Gd-infused polymer gel dosimeter and Monte Carlo study.

This work reports the experimental development of an integral Gd-infused dosimeter suitable for Gd dose enhancement assessment along with Monte Carlo simulations applied to determine the dose enhancement by radioactive and X-ray sources of interest in conventional and electronic brachytherapy. In this context, capability to elaborate a stable and reliable Gd-infused dosimeter was the first goal aimed at direct and accurate measurements of dose enhancement due to Gd presence. Dose-response was characterized for standard and Gd-infused PAGAT polymer gel dosimeters by means of optical transmission/absorbance. The developed Gd-infused PAGAT dosimeters demonstrated to be stable presenting similar dose-response as standard PAGAT within a linear trend up to 13 Gy along with good post-irradiation readout stability verified at 24 and 48 h. Additionally, dose enhancement was evaluated for Gd-infused PAGAT dosimeters by means of Monte Carlo (PENELOPE) simulations considering scenarios for isotopic and X-ray generator sources. The obtained results demonstrated the feasibility of obtaining a maximum enhancement around of (14 ±â€¯1)% for 192Ir source and an average enhancement of (70 ±â€¯13)% for 241Am. However, dose enhancement up to (267 ±â€¯18)% may be achieved if suitable filtering is added to the 241Am source. On the other hand, optimized X-ray spectra may attain dose enhancements up to (253 ±â€¯22) %, which constitutes a promising future alternative for replacing radioactive sources by implementing electronic brachytherapy achieving high dose levels.

Water-equivalence of gel dosimeters for radiology medical imaging.

International dosimetry protocols are based on determinations of absorbed dose to water. Ideally, the phantom material should be water equivalent; that is, it should have the same absorption and scatter properties as water. This study presents theoretical, experimental and Monte Carlo modeling of water-equivalence of Fricke and polymer (NIPAM, PAGAT and itaconic acid ITABIS) gel dosimeters. Mass and electronic densities along with effective atomic number were calculated by means of theoretical approaches. Samples were scanned by standard computed tomography. Photon mass attenuation coefficients and electron stopping powers were examined. Theoretical, Monte Carlo and experimental results confirmed good water-equivalence for all gel dosimeters. Overall variations with respect to water in the low energy radiology range (up to 130 kVp) were found to be less than 3% in average.

Radiation exposure of cardiac sonographers working in an academic noninvasive cardiovascular imaging laboratory.

BACKGROUND AND AIM: Exposure to workplace radiation among cardiac sonographers has been felt to be low, and patient-related sources have been considered negligible. Sonographers may be exposed to radiation from patient emitted sources as well as external sources in interventional laboratories. This study quantified radiation exposure to cardiac sonographers. METHODS: Cardiac sonographers, vascular imaging technologists, exercise physiologists, noninvasive nursing staff, and CT/MRI technologists were provided body dosimeter badges. Sonographers were provided dosimeter rings for their scanning hands. Radiation exposure was quantified from the dosimeter data, reported in millirems (mrem) for deep, eye, and shallow exposure, as well as shallow exposure data from the rings. Data were prospectively collected for 63 employees over a 12-month period and retrospectively analyzed. RESULTS: The mean annual deep body exposure in sonographers was 8.2 mrem/year, shallow exposure 9.8 mrem/year, eye exposure 8.5 mrem/year, and ring exposure 207 mrem/year. There was a significant difference between body and ring exposure (P = .0002). When comparing exposure data between the vascular imaging technologists, CT/MRI technologists, noninvasive nursing staff, and the cardiac sonographers, there were no statistical differences (P > .23). Exercise physiologists had significantly higher exposure compared to sonographers (P < .03). CONCLUSION: This single-center experience demonstrates that, while exposure is low, cardiac sonographers are exposed to workplace radiation, most likely from patient emitted radiation. The finding that radiation exposure from rings exceeded body exposure supports this conclusion. Continued education and assessment of work flow practices should be employed to minimize staff radiation exposure.

Experimental study on the performance of an epithermal neutron flux monitor for BNCT.

The performance of an epithermal neutron (0.5eV