Dosimetry Measurements Research Articles

Revision of PSI calculation capabilities and validation experience on the BEPU-type reactor dosimetry applications

The present paper summarizes the experience accumulated at the Laboratory for Reactor Physics and Thermal-Hydraulics (LRT) of the Paul Scherrer Institute in the field of reactor dosimetry, as well as outlines the recent progress achieved in relation to the associated nuclear data uncertainty propagation methodologies. For dosimetry simulations, the CASMO/SIMULATE/MCNP/FISPACT-II system of codes is in operation at LRT/Nuclear Energy and Safety (NES) Research Division, which is based on the use of validated CASMO/SIMULATE cycle-specific core-follow models of Swiss LWRs. Coupling with FISPACT-II provides the capability for detailed isotopic inventory tracking under irradiation, assessment of materials activation and dpa values, etc. The use of the seamless calculation scheme with translation of the core-follow simulation results into the detailed neutron source specifications for consequent Monte Carlo simulations, accomplished with nuclear data uncertainty propagation capabilities and integrated with appropriate dosimetry validation database, makes the PSI methodology well aligned with the generic best estimate plus uncertainty (BEPU) approach principles. For specific illustrations, this paper presents some results on evaluation of: 1) a few well-known OECD/NEA reactor shielding experimental benchmarks (SINBAD benchmarks H.B. Robinson-2, ASPIS-PCA REPLICA), 2) some dosimetry data obtained from a Swiss PWR and 3) simulation of the dosimetry measurements for the ‘PETALE’ experimental program at the EPFL research reactor ‘CROCUS’, as they were foreseen at the time of the experimental planning. Finally, ways to further enhance the simulation methodology and models are discussed.

Four decades of progress in PWRs surveillance program dosimetry measurements at the MADERE platform

Since 1981, the French Alternative Energies and Atomic Energy Commission has been measuring the dosimeters of the surveillance capsules of the French pressurized water reactors and assessing their neutron fluence. This represents more than 250 surveillance PWR capsules, i.e. 4 thousands dosimeters. Started in Grenoble, this work continued in Cadarache with the creation of the “Measurement Applied to DosimEtry in Reactors” (MADERE) platform within the Dosimetry, Sensors and Instrumentation Laboratory (LDCI). Since 1998, all surveillance dosimeters measurements (i.e. Al-Co, 238U, 237Np, Ni, Cu, Fe and Nb) have been performed at MADERE under the “Cofrac Essais” accreditation according to the ISO/IEC 17025 international standard. The evolution over time of the 1σ measurement uncertainty of the activity of each is presented in this paper. Since 2015, they are [±1.3% ; ±2.9%] for 238U with Ni encapsulation, [±0.8% ; ±2.1%] for 238U with Ti encapsulation, [±1.2% ; ±4.9%] for 238U with stainless steel encapsulation, ±1.3% for 237Np dosimeters, ±1.2% for Al-Co, [±1.2% ; ±1.4%] for nickel, copper and iron, [±3.3%; ±3.9%] for niobium if unbroken after irradiation.

Pembuatan In-House Phantom untuk Pengukuran Image Quality dan Dosimetri Sebagai Tool Optimasi Protokol Pemeriksaan CT Scan Thorak

The computed tomography scanner (CT scan) protocol used in patient examinations must be continuously reviewed and optimized. Medical physicists evaluate the quality of the resulting image using an image quality phantom and evaluate radiation dose using a dosimetry phantom separately. Procuring a dosimetry phantom and image quality phantom for CT scans separately also requires a lot of money. Therefore, developing a dosimetry phantom and image quality phantom combined in one phantom is expected to be a solution to overcome the mentioned problem. This research aims to create a phantom as a combination of a dosimetry phantom and an image quality phantom and to obtain an optimal CT scan protocol so that informative images can be obtained with minimal doses. The phantom that is made resembles the thoracic organs. The dose length product (DLP) and size-specific dose estimates (SSDE) measured from the phantom were compared with those from 100 patient images for chest CT scan examinations from January to December 2022 and measured using IndoseCT.The image quality of the phantom was measured using IndoQCT software. The estimated dosimetry data from the phantom are 122,5 mGy.cm and 10,94 mGy for DLP and SSDE, respectively, while the DLP and SSDE from patients are 143,5 mGy.cm and 9 mGy. Image quality test results for uniformity with a maximum difference in CT number of 4 HU. Maximum noise is 38,1 HU, and the minimum is 30 HU. The geometric accuracy measurement results are 0,4 mm from the actual size. Spatial Resolution of 0,8 lp/mm. The R2 value of contrast linearity is 0,9972. The Modulation Transfer Function (MTF10) measurement results are 0,63 mm--1. The results of the slice thickness test show the suitability between the measured results and the slice thickness setting on the CT Scan. An in-house phantom can be used in dosimetry and image quality measurements to optimize the thoracic CT scan protocol. Keywords: In-house phantom, Image quality, Dosimetry, Optimization

Strategies for safety thresholds of phonation for performers via dosimetry

Singers are among a category of professionals, along with many other professionals, who rely on their voice for work [1]. Phonotrauma can be caused by many factors, among which the amount and intensity of vocal use are at the forefront [2]. Dosimetry metrics can assist voice professionals aim for safe amounts of voice use, but a threshold of voice use has not yet been established and recommended by researchers [3]. Understanding what dosimetry research can offer is one important step towards that goal. Furthermore, once dosimetry devices become mainstream, singers can apply the understanding of dosimetry measurements to pace vocal use and minimize vocal fatigue, vocal effort, and consequently preventing vocal injury.

Implementing dispersion measurement as part of scanning proton therapy commissioning and quality assurance

Introduction. Dispersion in an accelerator quantifies the deviation of the proton trajectory when there is a momentum deviation. We present for the first time a safe method of measuring dispersion in the clinic, using a scintillator detector and the momentum deviations within a spill. This is an important accelerator quantity as we found that this is the reason behind the large dose fluctuation in our absolute dosimetry measurement. Methods. Dispersions are measured for nine energies in a Hitachi ProBeat system at three locations (isocenter and at two profile monitors) and at two gantry angles (0 and 90 degrees) by first measuring the spot position and momentum drift within a spill. The spot position drift is measured by the XRV-4000 at the isocenter, and by the two profile monitors located at 0.57 and 2.27 m from the isocenter. The momentum drift is calculated from the intra-spill range drift which is measured using the Ranger accessory. The dispersion at isocenter and its gradient are calculated using the weighted least square regression on the measured dispersions at the three locations. A constraint is formulated on the dispersion and its gradient to ensure minimal intra-spill spot position deviation around the isocenter. Results. The measured intra-spill range and spot positional drift at isocenter are less than and respectively. The momentum spread calculated from the range drift are less than 0.08%. The dispersion at the isocenter ranged from to and the zero-crossing happens upstream of isocenter for all energies. 2 of the 9 energies (168.0 and 187.5 MeV) violated the constraint and has an intra-spill spot positional deviation greater than within from the isocenter. Conclusion. This measurement is recommended as part of commissioning and annual quality assurance for accelerator monitoring and to ensure intra-spill spot deviations remain low.

Flow and temporal effects on the sonolytic defluorination of perfluorooctane sulfonic acid

The removal of per- and polyfluoroalkyl substance (PFAS) pollution from the environment is a globally pressing issue, due to some PFAS’ recalcitrant, bioaccumulative, and carcinogenic nature. Destruction via ultrasonic waves (sonolysis) is a promising contender for industrialisation due to; moderate power consumption, applicability to several PFAS and sample types, and limited by-products. Liquid flow rate through an ultrasonic reactor can affect the size, shape, and spatial distribution of ultrasonic cavities and hence their chemical activity. Such effects have not been studied during PFAS sonolysis, and temporal effects have not been studied much beyond the reactant concentration. Here, the effects of varying recirculating flow rate on the ultrasonic defluorination of perfluorooctane sulfonic acid (PFOS) and implications for industrial scale up are presented. Under the ultrasonic power (200 W L−1, 2.27 W cm−2) and frequency (410 kHz) used, flow rates of 79 and 214 ml min−1 enhanced defluorination up to 14 % during 30 min of treatment. However, these effects were temporal and most significant in the initial minutes of treatment. This indicated a dynamic bubble size distribution which stabilised after around 15 min. Defluorination rates of PFOS were compared with measured potassium iodide dosimetry, calorimetry, sonoluminescence (SL), and sonochemiluminescence (SCL). Flow rates which enhanced defluorination correlated moderately with enhanced SCL and negatively impacted SL, calorimetry, and dosimetry. Effects were attributed to perturbed cavity surfaces, leading to asymmetric cavity collapse, and the possibility of enhanced solvated electron production/interaction. SL, SCL, dosimetry, and calorimetric measurements were also temporal, and each showed different times to equilibrate. Flow rates of 439 and 889 ml min−1 returned all sonochemical measurements to the levels without flow, likely due to continued collapse temperature quenching by furthered bubble asymmetry. Flow also enhanced reactor cooling, which is significant for industrial temperature control. The pump energy consumed was small (≈1.9 %) compared to that of the amplifier and chiller, hence, PFOS defluorination was more cost-effective using flow. However, the effect may be limited for the longer treatment times needed for environmental remediation.

Dosimetric verification of annual quality assurance for a linear accelerator using a transmission type detector

The purpose of our study is to establish an efficient quality assurance (QA) procedure using a transmission-type detector (IBA, Stealth chamber), a reference signal detector, as a field chamber. Relative dosimetry items, including monitor unit linearity, output constancy based on dose rate and field size, and output factor were measured and compared with results obtained from the Farmer-type chamber (IBA, Wellhofer, FC65-G). Moreover, output for each field size was measured to assess its applicability to small fields. Results using the Stealth chamber were in good agreement with the FC65-G within 1.0%, except for output constancy according to gantry angle, which had a 1.1% error rate for the Stealth chamber and 2.7% for the FC65-G. Differences of up to − 6.26% output factor were observed for the Stealth chamber and up to − 0.56% for the CC-13 ionization chamber (IBA) in the 3 × 3 cm2 field. Our study confirmed the possibility of using Stealth chambers for relative dosimetry measurement in QA.

The assessment of the clinical impact of using a single set of radiotherapy planning data for two kilovoltage therapy units.

Kilovoltage therapy units are used for superficial radiotherapy treatment delivery. Peer reviewed studies for MV linear accelerators describe tolerances to dosimetrically match multiple linear accelerators enabling patient treatment on any matched machine. There is an absence of literature on using a single planning data set for multiple kilovoltage units which have limited ability for beam adjustment. This study reviewed kilovoltage dosimetry and treatment planning scenarios to evaluate the feasibility of using ACPSEM annual QA tolerances to determine whether two units (of the same make and model) were dosimetrically matched. The dosimetric characteristics, such as measured half value layer (HVL), percentage depth dose (PDD), applicator factor and output variation with stand-off distance for each kV unit were compared to assess the agreement. Independent planning data based on the measured HVL for each beam energy from each kV unit was prepared. Monitor unit (MU) calculations were performed using both sets of planning data for approximately 200 clinical scenarios and compared with an overall agreement between units of < 2%. Additionally, a dosimetry measurement comparison was completed at each site for a subset of nine scenarios. All machine characterisation measurements were within the ACPSEM Annual QA tolerances, and dosimetric testing was within 2.5%. This work demonstrates that using a single set of planning data for two kilovoltage units is feasible, resulting in a clinical impact within published uncertainty.

Results of extremity dosimetry based on the measurements at laboratory of individual and environmental dosimetry at IFJ PAN.

Laboratory of Individual and Environmental Dosimetry (LADIS) at the Institute of Nuclear Physics is the largest dosimetry service in Poland. Extremity ring dosimetry measurements are performed at LADIS laboratory for ˃20 years, with accredited procedure since 2002. According to the quality system based on PN-EN ISO/IEC 17025:2018-02 standard, Hp(0.07) personal dose equivalent is measured over the range of doses from 0.1 mSv to 1 Sv. Years of experience allow the laboratory to analyse the levels of doses received by workers in medical and industrial institutions cooperating with LADIS laboratory. Yearly, ˃30000 of extremity measurements have been performed for about 1000 institutions in Poland on the quarterly basis. According to the internal classification, the radiation workers under radiation protection control have been divided into a few groups. The analysis indicated that most of the doses received by exposed workers were on the level of the natural radiation background, but some of them exceeded the dose limit. The results show that ˃60% of Hp(0.07) doses were below 0.1mSv/quarter; however, some very high doses were also registered. The highest number of doses above 125mSv was observed in nuclear medicine and interventional radiology. The percentage of overdoses was relatively small but looking at individual cases the risk of unexpected irradiation was noticeable. Therefore, constant monitoring is always necessary.

Optimization of calibration interval based on equipment metrological history.

The purpose of this paper is to describe a method for optimizing the calibration period of a dosimetry measurement system with a focus on the personal dose equivalents Hp(d) and individual monitoring services. The systematic and analytical method developed provides a justification to the calibration interval based on experimental data and measurement uncertainties. Its main input is the metrological history of the equipment that is then used to predict the drift of the measurement system. The method is used to make the calibration operation more efficient over time in terms of cost and metrology. After a description of the method itself, the example of the OSL dosemeter reading process will be discussed and results will be shown. The method developed may be applied to other measurement processes no matter the technology used.

Dosimetry Reconstruction in Radiopharmaceutical Therapy Using a Sparse Network of External γ-Sensors

Radiopharmaceutical therapy (RPT) has demonstrated promise in the treatment of neuroendocrine and prostate cancer. Due to the highly varied biodistribution and non-homogeneity of total integrated dose across cancer patients, a system for real-time dosimetry based on continuous measurement is desirable to deliver sufficient dose for tumor ablation while preventing toxicity from off-target uptake by organs at risk (OAR). Single time point imaging (mostly SPECT)-based dosimetry offers a snapshot of the body-wide dose distribution at a given time point, but even single SPECT imaging is generally limited in availability, often leading to significant inaccuracies in estimating total integrated dose. Therefore, accurate personalized dosimetry in RPT is an unmet need and requires continuous dosimetry measurements of tumors and OARs across multiple half-lives of the therapeutic radiopharmaceutical. Using a priori knowledge of tumor and OAR locations from pretherapy imaging, we have developed a novel algorithm that utilizes a network of custom uncollimated, optical fiber-based γ-counting probes to isolate the real-time in vivo tumor and OAR uptake in 177Lu-PSMA-617 and 225Ac-MACROPA-YS5 therapy. The proposed system was successfully validated in athymic mice models bearing varying numbers of tumors from two human prostate cancer cell lines (PC3-pip, PC3-flu). Uncollimated γ counts using the developed probes were acquired outside of the mice for 10 minutes, starting at 0 hr, 6 hrs, 12 hrs, 24 hrs, and 48 hrs after the injection of 177Lu-PSMA-617. The percent injected activity per mL of tissue (%IA/mL) of each tumor and OAR was reconstructed at every time point and compared to the %IA/mL extracted from SPECT/CT immediately after the recording. The developed system's %IA/mL reconstruction in PC3-pip tumors, PC3-flu tumors, kidneys, and bladders is highly correlative with the %IA/mL extracted from state-of-art in vivo dosimetry techniques, with %IA/mL ranging from 0.1% to 160% assuming a 29.6 MBq 177Lu-PSMA-617 administration. The least squares linear regression fit between the reconstructed activity and the activity measured from SPECT/CT is given by Estimated %IA/mL = 0.91 x SPECT %IA/mL, with an R2 of 0.991, and Pearson's r of 0.9975. There is a nearly 1:1 mapping between the proposed model and SPECT/CT. A novel dose reconstruction algorithm for personalized dosimetry in RPT that utilizes a sparse set of external γ-counters and a priori knowledge of tumor and OAR locations was developed and validated in in vivo human prostate cancer murine models. The proposed system enables continuous dosimetry measurements of multiple tumors and OAR noninvasively, with high accessibility, high temporal resolution, and across multiple classes of ɑ and β-based RPT. Similar experiments using 225Ac-MACROPA-YS5 are ongoing and additional results will be reported.

Using Total Monte Carlo with hybrid calculation methods for constructing the covariance matrix of a neutron spectrum: Applications in spectrum adjustment

A new calculation scheme has been developed to improve the quality of covariance matrices of a-priori neutron spectra. A high quality covariance matrix is essential for guiding the adjustment of the a-priori calculated neutron spectrum to experimental dosimetry measurements in a physically realistic way. This new calculation scheme incorporates state-of-the-art hybrid deterministic/Monte Carlo methods and does not rely on prior knowledge of correlations between the different energy groups. The ADVANTG code was used to generate weight-windows for the full MCNP reactor model of the High Flux Reactor (HFR) in Petten, the Netherlands. This then allowed Total Monte Carlo (TMC) calculations to be performed with very low statistical uncertainties. A detailed demonstration of applying these covariance matrices to spectrum adjustment is also provided by utilising an algorithm adopted from the STAY’SL program. We have used the example of the HELIOS irradiation experiment performed at the HFR to demonstrate the approach here, but the flexibility of the method means it may be applied universally to neutron spectra calculated anywhere.

Preliminary study on dosimetry characteristics of a novel cylindrical dose verification system.

To develop a novel ionization chamber array dosimetry system, study its dosimetry characteristics, and perform preliminary tests for plan dose verification. The dosimetry characteristics of this new array were tested, including short-term and long-term reproducibility, dose linearity, dose rate dependence, field size dependence, and angular dependence. The open field and MLC field plans were designed for dose testing. Randomly select 30 patient treatment plans (10 intensity-modulated radiation therapy [IMRT] plans and 20 volumetric modulated arc therapy [VMAT] plans) that have undergone dose verification using Portal Dosimetry to perform verification measurement and evaluate dose verification test results. The dosimetry characteristics of the arrays all performed well. The gamma passing rates (3%/2mm) were more than 96% for the combined open field and MLC field plans. The average gamma pass rates were (99.54±0.58)% and (96.70±3.41)% for the 10 IMRT plans and (99.32±0.89)% and (94.91±6.01)% for the 20 VMAT plans at the 3%/2mm and 2%/2mm criteria, respectively, which is similar to the Portal Dosimetry's measurement results. This novel ionization chamber array demonstrates good dosimetry characteristics and is suitable for clinical IMRT and VMAT plan verifications.

Optically stimulated luminescence detectors for dosimetry and LET measurements in light ion beams

Objective. This work investigates the use of Al2O3:C and Al2O3:C,Mg optically stimulated luminescence (OSL) detectors to determine both the dose and the radiation quality in light ion beams. The radiation quality is here expressed through either the linear energy transfer (LET) or the closely related metric Q eff, which depends on the particle’s speed and effective charge. The derived LET and Q eff values are applied to improve the dosimetry in light ion beams. Approach. OSL detectors were irradiated in mono-energetic 1H-, 4He-, 12C-, and 16O-ion beams. The OSL signal is associated with two emission bands that were separated using a pulsed stimulation technique and subjected to automatic corrections based on reference irradiations. Each emission band was investigated independently for dosimetry, and the ratio of the two emission intensities was parameterized as a function of fluence- and dose-averaged LET, as well as Q eff. The determined radiation quality was subsequently applied to correct the dose for ionization quenching. Main results. For both materials, the Q eff determinations in 1H- and 4He-ion beams are within 5 % of the Monte Carlo simulated values. Using the determined radiation quality metrics to correct the nonlinear (ionization quenched) detector response leads to doses within 2 % of the reference doses. Significance. Al2O3:C and Al2O3:C,Mg OSL detectors are applicable for dosimetry and radiation quality estimations in 1H- and 4He-ions. Only Al2O3:C,Mg shows promising results for dosimetry in 12C-ions. Across both materials and the investigated ions, the estimated Q eff values were less sensitive to the ion types than the estimated LET values were. The reduced uncertainties suggest new possibilities for simultaneously estimating the physical and biological dose in particle therapy with OSL detectors.

The effect of spill change on reliable absolute dosimetry in a synchrotron proton spot scanning system.

Absolute dosimetry measurement is an integral part of Treatment Planning System (TPS) commissioning and it involves measuring the integrated absorbed dose to water for all energies in a pencil beam scanning delivery system. During the commissioning of Singapore's first proton therapy center, a uniform scanned field with an Advanced Markus chamber method was employed for this measurement, and a large dose fluctuation of at least 5% was observed for 10% of the energy layers during repeated measurements. This study aims to understand the root cause of this fluctuation by relating the actual delivered spot information in the log file with the charge measurement by the ion chambers. A dedicated pencil beam dose algorithm was developed, taking into account the log file parameters, to calculate the dose for a single energy layer in a homogeneous water phantom. Three energies, 70.2, 182.7, and 228.7 MeV were used in this study, with the 182.7 MeV energy exhibiting large dose fluctuation. The dose fluctuation was investigated as a function of detector's sizes (pinpoint 3D, Advanced Markus, PTW 34070, and PTW 34089) and water depth (2, 6, and 20cm). Twelve ion chambers measurements were performed for each chamber and depth. The comparison of the theoretically predicted integrated dose and the charge measurement served as a validation of the algorithm. About 5.9% and 9.6% dose fluctuation were observed in Advanced Markus and pinpoint 3D measurements at 2cm depth for 182.7 MeV, while fluctuation of 1.6% and 1.1% were observed in Advanced Markus with 228.7 and 70.2 MeV at similar depth. Fluctuation of less than 0.1% was observed for PTW34070 and PTW 34089 for all energies. The fluctuation was found to diminish with larger spot size at 20cm depth to 1.3% for 182.7 MeV. The theoretical and measured charge comparison showed a high linear correlation of for all datasets, indicating the fluctuation originated from the delivered spot characteristics. The cause of fluctuation was identified to be due to the spill change occurring close to the detector, and since the spot positional deviation profiles were different between two spills, this resulted in local hot spots between columns of spots. The actual position of spill change varies randomly during measurement, which led to a random occurrence of hot spot within the detector's sensitive volume and a fluctuating dose measurement. This is the first report of a dose fluctuation greater than 5% in absolute dosimetry measurement with a uniform scanned field and the cause of the fluctuation has been conclusively determined. It is important to choose the MU and scanning pattern carefully to avoid spill change happening when the spot delivery is near the detector.

METU-DBL: a cost effective proton irradiation facility

The Middle East Technical University Defocusing Beamline (METU-DBL) is designed to deliver protons with selectable kinetic energies between 15–30 MeV, and proton flux between 106–1010 protons/cm2/s, on a maximum 21.55 to 15.40 cm target region with a beam uniformity within ±6%, in accordance with the ESA ESCC No. 25100 specification for single event effects (SEEs) tests in the low energy range. The achieved high proton fluences, allow users to test space-grade materials; electronic circuits, ASICs, FPGAs, optical lenses, structural elements, and coating layers for LEO, GEO, and interplanetary missions.The total received dose on the Device-Under-Test (DUT) from secondary particles created during proton-material interactions at the first beam collimator and the beam dump never exceed 0.1% of the dose from primary protons. The METU-DBL is equiped with several measurement stations and services to the user teams. A secondary measurement station in a rotating drum that can hold multiple samples has been constructed next to the first collimator which provides neutrons for transmission experiments. At the target region, a robotic table is located, which provides mechanical and electrical mounting points to the samples and allows multiple samples to be tested in a row. A modular vacuum box can also be attached on the robotic table for any test that may require a vacuum environment. Power rails on the robotic table provide various outputs for the DUT. For the data acquisition, high-speed networking and a modular industrial PC are available at the target station. The design of the METU-DBL control software enables test users to integrate and optimize the data acquisition and controlling of the DUT.The beam properties at the target region are measured with the diamond, Timepix3, and fiber scintillator detectors mounted on the robotic table. With diamond and Timepix3 detectors, measurements are taken from the five different points (center and the four corners) of the test area to measure the proton flux and ensure that it is uniform across the full test area. Fiber scintillators on both axes (X and Y) scan the target area to cross-check the beam profile's uniformity. Secondary doses during the irradiation are measured by a Geiger-Müller tube sensitive to electrons and gammas above 0.1 MeV and by a neutron detector located at the entrance of the R&D room. The room cools down relatively fast after any irradiation (<1 hour).Accurate linear energy deposition rates and absorbed doses on the samples are calculated using MCNP6, FLUKA and Geant4 Monte Carlo simulations. Alanine dosimetry measurements that are calibrated against these simulations are also used to estimate the absorbed dose on the sample.

A Novel Anthropomorphic Phantom Composed of Tissue-Equivalent Materials for Use in Experimental Radiotherapy: Design, Dosimetry and Biological Pilot Study

The production of anthropomorphic phantoms generated from tissue-equivalent materials is challenging but offers an excellent copy of the typical environment encountered in typical patients. High-quality dosimetry measurements and the correlation of the measured dose with the biological effects elicited by it are a prerequisite in preparation of clinical trials with novel radiotherapy approaches. We designed and produced a partial upper arm phantom from tissue-equivalent materials for use in experimental high-dose-rate radiotherapy. The phantom was compared to original patient data using density values and Hounsfield units obtained from CT scans. Dose simulations were conducted for broad-beam irradiation and microbeam radiotherapy (MRT) and compared to values measured in a synchrotron radiation experiment. Finally, we validated the phantom in a pilot experiment with human primary melanoma cells.

Radiofrequency personal exposimetry during outdoor entertainment of young adults: a case study.

Radiofrequency (RF) exposure has grown substantially over time in the public area. Personal dosimetry measurements are intended to estimate how human RF exposure relates to exposure limits that do not pose a health risk. For our case study, an outdoor festival was chosen to assess realistic RF exposure of young adults during their entertainment. Band-selective RF exposure-sorted along 2G-4G uplinks and downlinks, 5G and Wi-Fi bands-was evaluated. Electric field strength data subsets were classified on the basis of activities as well as crowd density. 2G contributed the most to the overall RF exposure. Highest RF exposure was associated with attendance in a concert. In moderately crowded situations, RF exposure was higher than in the most crowded ones. However, the total measured electric field values were higher than in other outdoor environment, but still far below the national and international directives of regulatory RF-EMF exposure limits.

Towards quantitative in vivo dosimetry using x-ray acoustic computed tomography.

Radiation dosimetry is essential for radiation therapy (RT) to ensure that radiation dose is accurately delivered to the tumor. Despite its wide use in clinical intervention, the delivered radiation dose can only be planned and verified via simulation. This makes precision radiotherapy challenging while in-line verification of the delivered dose is still absent in the clinic. X-ray-induced acoustic computed tomography (XACT) has recently been proposed as an imaging tool for in vivo dosimetry. Most of the XACT studies focus on localizing the radiation beam. However, it has not been studied for its potential for quantitative dosimetry. The aim of this study was to investigate the feasibility of using XACT for quantitative in vivo dose reconstruction during radiotherapy. Varian Eclipse system was used to generate simulated uniform and wedged 3D radiation field with a size of 4 cm 4 cm. In order to use XACT for quantitative dosimetry measurements, we have deconvoluted the effects of both the x-ray pulse shape and the finite frequency response of the ultrasound detector. We developed a model-based image reconstruction algorithm to quantify radiation dose in vivo using XACT imaging, and universal back-projection (UBP) reconstruction is used as comparison. The reconstructed dose was calibrated before comparing it to the percent depth dose (PDD) profile. Structural similarity index matrix (SSIM) and root mean squared error (RMSE) are used for numeric evaluation. Experimental signals were acquired from 4 cm 4 cm radiation field created by Linear Accelerator (LINAC) at depths of 6, 8, and 10 cm beneath the water surface. The acquired signals were processed before reconstruction to achieve accurate results. Applying model-based reconstruction algorithm with non-negative constraints successfully reconstructed accurate radiation dose in 3D simulation study. The reconstructed dose matches well with the PDD profile after calibration in experiments. The SSIMs between the model-based reconstructions and initial doses are over 85%, and the RMSEs of model-based reconstructions are eight times lower than the UBP reconstructions. We have also shown that XACT images can be displayed as pseudo-color maps of acoustic intensity, which correspond to different radiation doses in the clinic. Our results show that the XACT imaging by model-based reconstruction algorithm is considerably more accurate than the dose reconstructed by UBP algorithm. With proper calibration, XACT is potentially applicable to the clinic for quantitative in vivo dosimetry across a wide range of radiation modalities. In addition, XACT's capability of real-time, volumetric dose imaging seems well-suited for the emerging field of ultrahigh dose rate "FLASH" radiotherapy.

A MONTE CARLO CALIBRATION APPROACH FOR A DUAL-ENERGY CT SYSTEM

This work shows the effectiveness of Monte Carlo methods for calibrating a dual-energy CT (DECT) system on a heterogeneous phantom for radiotherapy. The reference phantom comprising 20 inserts of different materials and densities representing human tissues inserted in a plastic water cylinder has been considered. The reliability of the model, built with the Penelope code, has been verified by comparing the results of the simulations at 80[Formula: see text]kVp and 140[Formula: see text]kVp with the experimental data acquired from the CT scans and dosimetry measurements. The effective atomic number from the various materials is also considered a control parameter. Tests for calibration and dose calculation are also based on a homogeneous phantom in PMMA and measurements in air with an ionization chamber. The Monte Carlo simulations coupled with dose evaluations allowed the calibration of the dose deposition effects on the considered tissue models.