A fast correction method of the scattering contributions in the area gamma dosemeter calibration field.

In the calibration procedure of area gamma dosemeters, how to accurately evaluate and correct the scattering contribution from the complex environmental factors to the point of test is the key problem to ensure the calibration accuracy. This paper proposed a fast correction method of the scattering contributions in the area gamma dosemeter calibration field. First, Monte Carlo method is employed to simulate the influence of scattering caused by different environmental factors in the calibration field, which is named as semi-panoramic reference radiation field. Then, a prediction model of the relationship between environmental factors and environmental scattering contribution is constructed based on the simulation data through the least squares support vector machine. With the model, the scattering contribution from the environmental factors can be fast estimated to correct the calibration results of the area gamma dosemeters, which will improve the accuracy of the calibration.

DEVIATION BETWEEN THE PLANNED DOSE AND THE IN VIVO DOSIMETRY RESULTS DURING POSTOPERATIVE IRRADIATION IN PATIENTS WITH UTERINE CANCER DEPENDING ON ANTHROPOMETRIC DATA. / VIDKhYLENNIa MIZh ZAPLANOVANOIu DOZOIu I REZUL'TATAMY DOZYMETRIÏ IN VIVO PRY PISLIaOPERATsIINOMU OPROMINENNI U PATsIIeNTOK, KhVORYKh NA RAK TILA MATKY, ZALEZhNO VID ANTROPOMETRYChNYKh DANYKh.

Topometry is an integral part of irradiation whose task is to repeat the position of the patient set by the simulator to repeat the PTV and the spatial relationship between the radiation field and the risk organs that were identified during planning. The dose distribution formulated in the plan is only an ideal model. There is some gap between the actual and planned dose distribution, especially in overweight patients. OBJECTIVE: evaluate the effect of anthropometric data on the deviation between the planned dose and the results of dosimetry in vivo in patients with uterine cancer during postoperative irradiation. MATERIALS AND METHODS: The authors analyzed the results of treatment of 110 patients with stage IB-II uterine can- cer who were treated at the Department of Radiation Therapy of the Institute of Medical Radiology and Oncology of the National Academy of Medical Sciences of Ukraine from 2016 to 2019. The technique of classical fractionation was used with a single focal dose of 2.0 Gy 5 times a week, the total focal dose was 42.0-50.0 Gy. To assess the effect of the patient's anthropometric data on the difference between the actual and calculated dose, the authors per- formed in vivo dosimetry after the first session and in the middle of the postoperative course of external beam radi- ation therapy. RESULTS: Рatients with BSA < 1.92 m2, had the median relative deviation at the first session -4.12 %, after 20.0 Gy - 3.61 %, patients with BSA > 1.92 m2: -2.06 % and -1.55 % respectively. After 20 Gy 34.8 % of patients with BSA < 1.92 m2 there was an increase in deviation from the planned dose, 65.2 % a decrease, while in 56.1 % of patients with BSA > 1.92 m2 there was an increase, and in 43.9 % - its reduction. With increasing BMI, the actual dose received on the rectal mucosa in the tenth session of irradiation is approaching the calculated one. CONCLUSIONS: When irradiated on the ROKUS-AM device, we did not find a probable dependence of the influence of the constitutional features of patients between the received and planned radiation dose. When treated with a Clinac 600 C, only body weight and body mass index at the tenth irradiation session have a likely effect on the dose differ- ence. Therefore, issues related to the individual approach to the treatment of uterine cancer, depending on anthro- pometric data is an urgent problem of modern radiotherapy.

Fricke gel xylenol orange dosimeter layers for stereotactic radiosurgery: A preliminary approach.

Investigations regarding the feasibility, reliability, and accuracy of Fricke gel dosimeter layers for stereotactic radiosurgery are presented. A representative radiosurgery plan consisting of two targets has been investigated. Absorbed dose distributions measured using radiochromic films and gelatin Fricke Gel dosimetry in layers have been compared with dose distributions calculated by using a treatment planning system and Monte Carlo simulations. The different dose distributions have been compared by means of the gamma index demonstrating that gelatin Fricke gel dosimeter layers showed agreements of 100%, 100%, and 93%, with dose and distance tolerances of 2% and 2 mm, with respect to film dosimetry, treatment planning system and Monte Carlo simulations, respectively. The capability of the developed system for three-dimensional dose mapping was shown, obtaining promising results when compared with well-established dosimetry methods. The obtained results support the viability of Fricke gel dosimeter layers analyzed by optical methods for stereotactic radiosurgery.

Real-time quantitation of thyroidal radioiodine uptake in thyroid disease with monitoring by a collar detection device.

Radioactive iodine (RAI) is safe and effective in most patients with hyperthyroidism but not all individuals are cured by the first dose, and most develop post-RAI hypothyroidism. Postoperative RAI therapy for remnant ablation is successful in 80-90% of thyroid cancer patients and sometimes induces remission of nonresectable cervical and/or distant metastatic disease but the effective tumor dose is usually not precisely known and must be moderated to avoid short- and long-term adverse effects on other tissues. The Collar Therapy Indicator (COTI) is a radiation detection device embedded in a cloth collar secured around the patient's neck and connected to a recording and data transmission box. In previously published experience, the data can be collected at multiple time points, reflecting local cervical RAI exposure and correlating well with conventional methods. We evaluated the real-time uptake of RAI in patients with hyperthyroid Graves' disease and thyroid cancer. We performed a pilot feasibility prospective study. Data were analyzed using R© (version 4.0.3, The R Foundation for Statistical Computing, 2020), and Python (version 3.6, Matplotlib version 3.0.3). The COTI was able to provide a quantitative temporal pattern of uptake within the thyroid in persons with Graves' disease and lateralized the remnant tissue in persons with thyroid cancer. The study has demonstrated that the portable collar radiation detection device outside of a healthcare facility is accurate and feasible for use after administration of RAI for diagnostic studies and therapy to provide a complete collection of fractional target radioactivity data compared to that traditionally acquired with clinic-based measurements at one or two time-points.Clinical Trials Registration NCT03517579, DOR 5/7/2018.

Semiconductor dosimetry in modern external-beam radiation therapy.

Semiconductor dosimeters are ubiquitous in modern external-beam radiation therapy. They possess key features. The response, electronically available in real time, is stable and linear with absorbed dose for given irradiation conditions; the radiation-sensitive volume can be rather small in size, while retaining mechanical strength and high sensitivity. We describe three common semiconductor dosimeters: diodes, metal-oxide-semiconductor field-effect transistors and diamonds. We discuss in detail their operation principles and applications in modern external-beam radiation therapy, primarily with megavoltage photon beams. We also explore their use in proton and heavy ion therapy, and in experimental radiotherapy techniques such as synchrotron-based micro-beam radiation therapy.

Physical characterization of a novel wireless DRX Plus 3543C using both a carbon nano tube (CNT) mobile x-ray system and a traditional x-ray system.

This work aims to characterize the novel DRX Plus 3543C detector in terms of detective quantum efficiency (DQE) using both a mobile x-ray system called Carestream DRX Revolution Nano and a traditional x-ray system (Carestream DRX Evolution). We used the commercial system DRX Revolution Nano, equipped with a new x-ray source based on CNT technology and field emission (FE) as the electron emitter (cathode). An innovative aspect of this device is its intrinsic selection of the focal spot size. We tested the system using three IEC-specified beam qualities (RQA3, 5 and 7) in terms of modulation transfer function (MTF), normalized noise power spectra (NNPS) and DQE as defined in the IEC 62220-1-1:2015. We compared the results obtained using DRX Revolution Nano and DRX Evolution with correlation and with Bland-Altman plots to study their agreement. RQA3 MTF is slightly lower than the RQA5 and 7 curves between 0.5 and 2.5 cycles mm-1. We measured MTF values of about 0.6 at 1 lp mm-1 and about 0.28 lp mm-1 at 2 lp mm-1. The NNPS curves show a decreasing trend with the energy regarding the DRX Revolution Nano. On the other hand, the DRX Evolution NNPS curve at RQA3 is greater than the one at RQA5, but the one at RQA5 is less than the one at RQA7. The DQE(0) ranged between about 0.82 (DRX Evolution at RQA3) and 0.54 (DRX Evolution at RQA7). As expected, the squared Pearson's correlation coefficients between the two x-ray tubes were always in an optimal agreement, and Bland-Altman plots confirmed a substantial equivalence between the two physical characterizations of the wireless detector. In conclusion, we can show that the dynamic focal selection of the system equipped with CNT does not play a substantial role in image quality compared to a traditional system in terms of physical characterisation of the detector in our measurement conditions.

Alanine dosimetry in strong magnetic fields: use as a transfer standard in MRI-guided radiotherapy.

Reference dosimetry in the presence of a strong magnetic field is challenging. Ionisation chambers have shown to be strongly affected by magnetic fields. There is a need for robust and stable detectors in MRI-guided radiotherapy (MRIgRT). This study investigates the behaviour of the alanine dosimeter in magnetic fields and assesses its suitability to act as a reference detector in MRIgRT. Alanine pellets were loaded in a waterproof holder, placed in an electromagnet and irradiated by 60Co and 6 MV and 8 MV linac beams over a range of magnetic flux densities. Monte Carlo simulations were performed to calculate the absorbed dose, to water and to alanine, with and without magnetic fields. Combining measurements with simulations, the effect of magnetic fields on alanine response was quantified and a correction factor for the presence of magnetic fields on alanine was determined. This study finds that the response of alanine to ionising radiation is modified when the irradiation is in the presence of a magnetic field. The effect is energy independent and may increase the alanine/electron paramagnetic resonance (EPR) signal by 0.2% at 0.35 T and 0.7% at 1.5 T. In alanine dosimetry for MRIgRT, this effect, if left uncorrected, would lead to an overestimate of dose. Accordingly, a correction factor, [Formula: see text], is defined. Values are obtained for this correction as a function of magnetic flux density, with a standard uncertainty which depends on the magnetic field and is 0.6% or less. The strong magnetic field has a measurable effect on alanine dosimetry. For alanine which is used to measure absorbed dose to water in a strong magnetic field, but which has been calibrated in the absence of a magnetic field, a small correction to the reported dose is required. With the inclusion of this correction, alanine/EPR is a suitable reference dosimeter for measurements in MRIgRT.

MOSFET dosimeter characterization in MR-guided radiation therapy (MRgRT) Linac.

PURPOSE: With the increasing use of MR-guided radiation therapy (MRgRT), it becomes important to understand and explore accuracy of medical dosimeters in the presence of magnetic field. The purpose of this work is to characterize metal-oxide-semiconductor field-effect transistors (MOSFETs) in MRgRT systems at 0.345 T magnetic field strength. METHODS: A MOSFET dosimetry system, developed by Best Medical Canada for in-vivo patient dosimetry, was used to study various commissioning tests performed on a MRgRT system, MRIdian® Linac. We characterized the MOSFET dosimeter with different cable lengths by determining its calibration factor, monitor unit linearity, angular dependence, field size dependence, percentage depth dose (PDD) variation, output factor change, and intensity modulated radiation therapy quality assurance (IMRT QA) verification for several plans. MOSFET results were analyzed and compared with commissioning data and Monte Carlo calculations. RESULTS: MOSFET measurements were not found to be affected by the presence of 0.345 T magnetic field. Calibration factors were similar for different cable length dosimeters either placed at the parallel or perpendicular direction to the magnetic field, with variations of less than 2%. The detector showed good linearity (R2  = 0.999) for 100-600 MUs range. Output factor measurements were consistent with ionization chamber data within 2.2%. MOSFET PDD measurements were found to be within 1% for 1-15 cm depth range in comparison to ionization chamber. MOSFET normalized angular response matched thermoluminescent detector (TLD) response within 5.5%. The IMRT QA verification data for the MRgRT linac showed that the percentage difference between ionization chamber and MOSFET was 0.91%, 2.05%, and 2.63%, respectively for liver, spine, and mediastinum. CONCLUSION: MOSFET dosimeters are not affected by the 0.345 T magnetic field in MRgRT system. They showed physics parameters and performance comparable to TLD and ionization chamber; thus, they constitute an alternative to TLD for real-time in-vivo dosimetry in MRgRT procedures.

Assessing recall of personal sun exposure by integrating UV dosimeter and self-reported data with a network flow framework.

BACKGROUND: Melanoma survivors often do not engage in adequate sun protection, leading to sunburn and increasing their risk of future melanomas. Melanoma survivors do not accurately recall the extent of sun exposure they have received, thus, they may be unaware of their personal UV exposure, and this lack of awareness may contribute towards failure to change behavior. As a means of determining behavioral accuracy of recall of sun exposure, this study compared subjective self-reports of time outdoors to an objective wearable sensor. Analysis of the meaningful discrepancies between the self-report and sensor measures of time outdoors was made possible by using a network flow algorithm to align sun exposure events recorded by both measures. Aligning the two measures provides the opportunity to more accurately evaluate false positive and false negative self-reports of behavior and understand participant tendencies to over- and under-report behavior. METHODS: 39 melanoma survivors wore an ultraviolet light (UV) sensor on their chest while outdoors for 10 consecutive summer days and provided an end-of-day subjective self-report of their behavior while outdoors. A Network Flow Alignment framework was used to align self-report and objective UV sensor data to correct misalignment. The frequency and time of day of under- and over-reporting were identified. FINDINGS: For the 269 days assessed, the proposed framework showed a significant increase in the Jaccard coefficient (i.e. a measure of similarity between self-report and UV sensor data) by 63.64% (p < .001), and significant reduction in false negative minutes by 34.43% (p < .001). Following alignment of the measures, under-reporting of sun exposure time occurred on 51% of the days analyzed and more participants tended to under-report than to over-report sun exposure time. Rates of under-reporting of sun exposure were highest for events that began from 12-1pm, and second-highest from 5-6pm. CONCLUSION: These discrepancies may reflect lack of accurate recall of sun exposure during times of peak sun intensity (10am-2pm) that could ultimately increase the risk of developing melanoma. This research provides technical contributions to the field of wearable computing, activity recognition, and identifies actionable times to improve participants' perception of their sun exposure.

CHARACTERISATION AND EVALUATION OF AL2O3:C-BASED OPTICALLY STIMULATED LUMINESCENT DOSEMETER SYSTEM FOR DIAGNOSTIC X-RAYS: PERSONAL AND IN VIVO DOSIMETRY.

This study characterises and evaluates an Al2O3:C-based optically stimulated luminescent dosemeter (OSLD) system, commercially known as the nanoDot™ dosemeter and the InLight® microStar reader, for personal and in vivo dose measurements in diagnostic radiology. The system characteristics, such as dose linearity, reader accuracy, reproducibility, batch homogeneity, energy dependence and signal stability, were explored. The suitability of the nanoDot™ dosemeters was evaluated by measuring the depth dose curve, in vivo dose measurement and image perturbation. The nanoDot™ dosemeters were observed to produce a linear dose with ±2.8% coefficient variation. Significant batch inhomogeneity (8.3%) was observed. A slight energy dependence (±6.1%) was observed between 60 and 140 kVp. The InLight® microStar reader demonstrated good accuracy and a reproducibility of ±2%. The depth dose curve measured using nanoDot™ dosemeters showed slightly lower responses than Monte Carlo simulation results. The total uncertainty for a single dose measurement using this system was 11%, but it could be reduced to 9.2% when energy dependence correction was applied.

RESULTS OF THE JOINT IAEA/ARPANSA INTERCOMPARISON EXERCISE ON WHOLE BODY DOSEMETERS FOR PHOTONS IN ASIA AND THE PACIFIC REGION.

An intercomparison exercise (IC) on whole body dosemeters to determine the quantity personal dose equivalent Hp (10) in photon radiation fields was jointly organised and conducted by the International Atomic Energy Agency (IAEA) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) for individual monitoring services (IMS) in Asia and the Pacific region. This was arranged to help the IMS in the region to achieve a more accurate dosimetry service and to improve their performance. Twenty-four IMS participated in this IC. Four sets of dosemeters were irradiated using X-ray and gamma radiation qualities at 0° and 20° angle of incidence, respectively. All the IMS provided results that were within the acceptable limits defined by the IAEA. However, only a minority of participants reported confidence intervals that included the reference dose, for each exposure scenario. For few systems, the overall performance could be significantly improved by reviewing calibration procedures.

A very low diffusion Fricke gel dosimeter with functionalised xylenol orange-PVA (XOPVA).

A gel dosimeter has been developed utilising a recently reported system for reducing Fe3+ diffusion in a Fricke gel dosimeter which chelates xylenol orange to the gelling agent poly(vinyl alcohol) (PVA). Formulations were investigated using both gelatin and PVA as the gelling agent, along with the inclusion of glyoxal. The resulting gel had an optical density dose response of 0.0031 Gy-1, an auto-oxidation rate of 0.000 23 h-1, and a diffusion rate of 0.132 mm2 h-1 which is a significant improvement over previously reported gelatin based Fricke gel dosimeters. The gel was also shown to be energy and dose-rate independent and could be reused after irradiation. Thus, this gel dosimeter has the potential to provide a safe and practical solution to three dimensional radiation dosimetry in the medical environment.

Low-density gel dosimeter for measurement of the electron return effect in an MR-linac.

Radiation therapy in the presence of a strong magnetic field is known to cause regions of enhanced and reduced dose at interfaces of materials with varying densities, in a phenomenon known as the electron return effect (ERE). In this study, a novel low-density gel dosimeter was developed to simulate lung tissue and was used to measure the ERE at the lung-soft tissue interface. Low-density gel dosimeters were developed with Fricke xylenol orange gelatin (FXG) and ferrous oxide xylenol orange (FOX) gels mixed with polystyrene foam beads of various sizes. The gels were characterized based on CT number, MR signal intensity, and uniformity. All low-density gels had CT numbers roughly equivalent to lung tissue. The optimal lung-equivalent gel formulation was determined to be FXG with <1 mm polystyrene beads due to the higher signal intensity of FXG compared to FOX and the higher uniformity with the small beads. Dose response curves were generated for the optimal low-density gel and conventional FXG. The change in spin-lattice relaxation rate (R1) before and after irradiation was linear with dose for both gels. Next, phantoms consisting of concentric cylinders with low-density and conventional FXG were created to simulate the lung-soft tissue interface. The phantoms were irradiated in a conventional linear accelerator (linac) and in a linac combined with a 1.5 T magnetic resonance imaging (MRI) unit (MR-linac) to measure the effects of the magnetic field on the dose distribution. Hot and cold spots were observed in the dose distribution at the boundaries between the gels for the phantom irradiated in the MR-linac but not the conventional linac, consistent with the ERE.

Monte Carlo characterization and benchmarking of extended range REM meters for its application in shielding and radiation area monitoring in Compact Proton Therapy Centers (CPTC).

Compact Proton Therapy Centers, CPTC, have a single treatment room, and are technologically more affordable, smaller, advanced and easier to use. From a radiological protection point of view, the leading concern in CPTC are interactions of protons with components of the facility and patients that yield a broad emission of secondary particles, mainly high-energy neutrons, up to 230 MeV, and photons. Optimal design of shielding involves theoretical assumptions in the design phase and, consequently, experimental measurements with extended range neutron detectors must be carried out in the facility during the commissioning period to verify the design, assumptions and building of the enclosures. There are almost 50 CPTC under construction and planning around the world, hence the improvement of methodologies to verify the shielding and to evaluate the dose to workers and general public in CPTC is a trending issue. The aim of this work was to evaluate and compare the response of two commercial extended range REM meters, WENDI-II and LUPIN-II, for their application in shielding verification and radiation area monitoring in CPTC facilities, by estimating the ambient dose equivalent, H*(10), through the Monte Carlo code MCNP6. The results have been compared with previous works. Likewise, the performance evaluation of these devices in continuous energy neutron field have been carried out, using the AmBe/241 neutron source of the Neutronics Hall (NH) of the Neutron Measurements Laboratory of the Energy Engineering Department of Universidad Politecnica de Madrid (LMN-UPM), through Monte Carlo simulation with the MCNP6 code and experimental measurements. The work is framed into the project Contributions to Shielding and Dosimetry of Neutrons in CPTC.

Leuco crystal violet-Pluronic F-127 3D radiochromic gel dosimeter.

This work reports results related to the manufacturing and optimisation of a leuco crystal violet (LCV)-Pluronic F-127 radiochromic gel dosimeter suitable for 3D radiotherapy dosimetry. A feature of this gel is that the natural gelatine polymer, which is most often used as a matrix in 3D dosimeters, is substituted with Pluronic F-127 synthetic copolymer (poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide). Pluronic F-127 ensures a higher transparency than gelatine, which may be beneficial for optical computed tomography readout, and improves the thermal properties in the temperature range above ~30 °C at which the gelatine physical gel converts to a solution. The optimal composition obtained comprises 2 mM LCV, 4 mM 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100), 17 mM trichloroacetic acid (TCAA) and 25% Pluronic F-127. Its main dose-response features are 4‒150 Gy linear dose range (150 Gy was the maximal dose applied to gels in this work), 0.0070 Gy-1 cm-1 dose sensitivity (derived from absorbance (600 nm) = f (dose) for 6 MeV electrons, 0.88(3) Gy s-1 and 0.0156 Gy-1 cm-1 derived from optical density (Δµ) = f (dose) for 6 MV x-rays, 0.1010 Gy s-1), low initial colour (initial absorbance = 0.0429) and a diffusion coefficient of crystal violet (CV) in LCV-Pluronic of 0.054 ± 0.023 mm2 h-1. Raman spectroscopy was used to characterize LCV-Pluronic chemical changes after irradiation. Differential scanning calorimetry (DSC) revealed that LCV-Pluronic is stable in temperatures between approximately 11 °C and 56 °C. Irradiation of LCV-Pluronic gel impacts on its first sol-gel transition temperature and the thermal effect of this process-both increased with absorbed dose, which might be related to the degradation of Pluronic. LCV-Pluronic is a promising 3D dosimeter for ionising radiation applications. Further work is needed to improve LCV-Pluronic response in the low dose region, and characterize potential effects of pH, temperature during irradiation, and radiation quality/dose rate on dose response characteristics.

Radiological tissue equivalence of deformable silicone-based chemical radiation dosimeters (FlexyDos3D).

FlexyDos3D, a silicone-based chemical radiation dosimeter, has great potential to serve as a three-dimensional (3D) deformable dosimetric tool to verify complex dose distributions delivered by modern radiotherapy techniques. To facilitate its clinical application, its radiological tissue needs to be clarified. In this study we investigated its tissue-equivalence in comparison with water and Solid Water (RMI457). We found that its effective and mean atomic numbers were 40% and 20% higher and the total interaction probabilities for kV x-ray photons were larger than those of water respectively. To assess the influence of its over-response to kV photons, its HU value was measured by kV computed tomography (CT) and was found higher than all the soft-tissue substitutes. When applied for dose calculation without correction, this effect led to an 8% overestimation in electron density via HU-value mapping and 0.65% underestimation in target dose. Furthermore, depth dose curves (PDDs) and off-axis ratios (profiles) at various beam conditions as well as the dose distribution of a full-arc VMAT plan in FlexyDos3D and reference materials were simulated by Monte Carlo, where the results showed great agreement. As indicated, FlexyDos3D exhibits excellent radiological water-equivalence for clinical MV x-ray dosimetry, while its nonwater-equivalent effect for low energy x-ray dosimetry requires necessary correction. The key findings of this study provide pertinent reference for further FlexyDos3D characterization research.

The Influence of Magnetic Fields (0.05 T ≤ B ≤ 7 T) on the Response of Personal Thermoluminescent Dosimeters to Ionizing Radiation.

We investigated the main question of whether thermoluminescent dosimeters indicate the correct dose when exposed to magnetic fields from low stray fields up to high magnetic resonance imaging fields inside human magnetic resonance imaging scanners (0.05 T ≤ B ≤ 7 T) during and after irradiation. Medical personnel working in radiology, oncology, or nuclear medicine are regularly monitored with thermoluminescent dosimeters. They might also enter the magnetic field of a magnetic resonance imaging scanner while supervising patients as well as during positron emission tomography-magnetic resonance imaging and magnetic resonance imaging-linac integrated imaging systems and will therefore be exposed to the magnetic fields of magnetic resonance imaging scanners and low stray fields of several millitesla outside of the magnetic resonance imaging scanner, not only before and after, but also during irradiation. Panasonic thermoluminescent dosimetry badges and ring dosimeters for personal monitoring were exposed to magnetic fields originating from a 7 T and a 3 T magnetic resonance imaging scanner as well as neodymium permanent magnets. Four different sealed Cs sources were used in two sets of experiments: (1) magnetically induced fading: irradiated thermoluminescent dosimeters (D ≈ 100 mSv) were exposed to a strong magnetic field (B = 7 T) of a human high-field magnetic resonance imaging scanner after irradiation; no magnetically induced fading (magnetoluminescence) for LiBO:Cu or CaSO:Tm was observed; (2) magnetically induced attenuation: thermoluminescent dosimeters were placed during irradiation in a magnetic field for about 60 h; a significantly reduced dose response was observed for LiBO:Cu-interestingly not at maximum B ≈ 7 T but at B ≈ 0.2 T. This experimental observation is possibly relevant especially for medical and technical personnel in nuclear medicine before and during a magnetic resonance imaging scanning procedure. Follow-up studies need to be made to clarify the kinetics of this effect.

Optimizing the response, precision, and cost of a DNA double-strand break dosimeter.

We developed a dosimeter that measures biological damage following delivery of therapeutic beams in the form of double-strand breaks (DSBs) to DNA. The dosimeter contains DNA strands that are labeled on one end with biotin and on the other with fluorescein and attached to magnetic microbeads. Following irradiation, a magnet is used to separate broken from unbroken DNA strands. Then, fluorescence is utilized to measure the relative amount of broken DNA and determine the probability for DSB. The long-term goal for this research is to evaluate whether this type of biologically based dosimeter holds any advantages over the conventional techniques. The purpose of this work was to optimize the dosimeter fabrication and usage to enable higher precision for the long-term research goal. More specifically, the goal was to optimize the DNA dosimeter using three metrics: the response, precision, and cost per dosimeter. Six aspects of the dosimeter fabrication and usage were varied and evaluated for their effect on the metrics: (1) the type of magnetic microbeads, (2) the microbead to DNA mass ratio at attachment, (3) the type of suspension buffer used during irradiation, (4) the concentration of the DNA dosimeter during irradiation, (5) the time waited between fabrication and irradiation of the dosimeter, and (6) the time waited between irradiation and read out of the response. In brief, the best results were achieved with the dosimeter when attaching 4.2 µg of DNA with 1 mg of MyOne T1 microbeads and by suspending the microbead-connected DNA strands with 200 µl of phosphate-buffered saline for irradiation. Also, better results were achieved when waiting a day after fabrication before irradiating the dosimeter and also waiting an hour after irradiation to measure the response. This manuscript is meant to serve as guide for others who would like to replicate this DNA dose measurement technique.

Water equivalent radiological properties of Gafchromic external beam therapy and external beam therapy 2 film dosimeters.

BACKGROUND: Water equivalent property of any clinical dosimeter is important. Water has the approximately similar radiation absorption and scattering properties to soft tissue. Film dosimeter plays a significant role in radiotherapy quality assurance and treatment plan verification. AIMS: In this study, we are evaluating the water equivalent radiological properties of Gafchromic electronic benefit transfer (EBT) and EBT2 film dosimeters. MATERIALS AND METHODS: Radiological properties such as number of electrons per gram (ne), electron density (ϼe), and effective atomic number (Zeff) are calculated using Mayneord formula. Mixture rule is used to calculate the mass absorption coefficient (µen/ϼ) and mass attenuation coefficient (µ/ϼ), and data are generated using Win-XCom over 10 KeV to 20 MeV. Electron stopping power data are generated with the help of ESTAR database over 10 KeV to 30 MeV. Those results are compared with water and deviations are found. RESULTS: Our results suggest that Zeff, ne, and ϼe of EBT is showing deviations <8.83%, 4.39%, and 16.18% and for EBT2 is 4.26%, 2.82%, and 19.41% with respect to water. Deviation in µen/ϼ and µ/ϼ of EBT and EBT2 film is ≤5% and ≤6%, respectively, with respect to water >100 KeV. Electron stopping power properties are also close in agreements with water having deviations ≤5%. CONCLUSION: Presence of high atomic number element chlorine, potassium, and bromine may disturb the water equivalent properties in the lower energy range <100 KeV and similarly enhance the dose sensitivity because of the strong photoelectric absorption process.

Comparison of thermoluminescent dosimeter calibration irradiated in gamma knife and 60Co instruments.

AIM: By necessity of dosimeters calibration for evaluating delivered dose accuracy to organs out of the radiation field in patients undergoing gamma knife radiosurgery, we calibrated thermoluminescence dosimeters in gamma knife and 60Co instruments, and then, compared both results to investigate when one of these devices was out of reach, can we use one of this instruments instead of the ther. MATERIALS AND METHODS: To individual calibration by 60Co, thermoluminescent dosimeters (TLDs) were placed in a Perspex sheet with conditions of source-skin distance = 80 cm, field size = 10 cm × 10 cm, and dose = 100 cGy. For individual calibration by Gamma knife, TLDs placed in flat Perspex were located in a special sphere and were exposed with conditions of source to axis distance = 40 cm, field size = 18 mm, and dose = 100 cGy, and for group calibration, TLDs were divided into six groups and were exposed with doses of 0-1000 cGy in both devices. RESULTS: According to Fisher's exact test, calculated P = 0.27, so the difference is not significant. CONCLUSIONS: The result showed despite differences in calibration conditions, 60Co unit can be used to calibrate TLD dosimeter for estimating the accuracy of measurement of delivered dose to organs of patients undergoing Gamma Knife 4C radiosurgery treatment.