Air Kerma Rate Research Articles

Characterization of X-ray Beams: Determination of K\(_{a,e}\) for Comparison with DRLs

Aims: The aim of this experimental study was to quantify the entrance surface air kerma (Ka,e) of X-ray beams in radiographic examinations, and the obtained values were compared with national and international Diagnostic Reference Levels (DRLs). Place and Duration of Study: Sample: Department of Medical Physics and Radiology, Franciscan University (UFN), between June 2023 and August 2024. Methodology: Initially, the main quality control (QC) tests were applied to characterize the radiographic equipment. During the evaluation of the X-ray beam, a dosimetric set was used, and for the same QC geometry, Air Kerma Rate (KAIR) measurements were obtained to determine the output of the X-ray tube. Under the same conditions, a phantom without water and the same filled with water were used to determine the backscatter factor (BSF), which was then used to estimate the Ka,e for the main radiographic examinations. Results: The results of this study are consistent with other studies and identified the region/anatomy with the highest radiation exposure, highlighting the importance of its optimization and verifying that continued professional training should be integrated into best practices to ensure greater safety in procedures. The results obtained evidence the necessity for adjustments in image acquisition protocols, as the Ka,e values found in this study, although within the limits established by the national DRLs, exceed the reference values of countries such as the United Kingdom and Japan in the areas of the skull, abdomen, and lumbar spine. This discrepancy highlights the importance of the periodic review and update of DRLs, in accordance with international recommendations and the technological evolution of equipment. Dose optimization is an ongoing process that involves the evaluation of image quality, the appropriate selection of technical parameters, and the implementation of specific dose protocols. The continuous training of radiology professionals is essential to ensure the correct application of imaging techniques and the minimization of patient exposure to ionizing radiation. Conclusion: This study shows the importance of evaluating radiation dose in diagnostic imaging and the need for a multidisciplinary approach to dose optimization. Implementing quality assurance programs, updating DRLs, and providing ongoing training for professionals are essential to ensure patient safety and high-quality diagnostic imaging. The methodology adopted in this study can contribute to the ongoing education of radiology professionals, promoting the correct application of imaging techniques and reducing patient exposure to ionizing radiation.

BSP – Computer code for evaluating protection against bremsstrahlung radiation from extended beta radiation sources

For a long time, radiation safety specialists have been aware of computer codes designed to calculate human dose exposure from beta or gamma radiation. However, these products have a major drawback: they do not consider the radiation fields generated by extended beta radiation sources due to bremsstrahlung. Existing solutions are either not widely available or use outdated nuclear-physical constants and methods for calculating dosimetric characteristics. A computer code was developed specifically for calculating shielding against bremsstrahlung. It allows to estimate effective, equivalent, exposure dose rate, ambient dose equivalent, and air kerma rate from bremsstrahlung. It utilizes the ANS/ANSI 6.4.3 materials data and the last dose conversion factors from ICRP 116.

Establishment of a 241Am gamma calibration field based on international standards and its conversion coefficients.

A 241Am gamma (γ)-ray calibration field that meets the requirements for a γ-ray reference field as specified in the ISO 4037 standard series was established in the Facility of Radiation Standards of the Japan Atomic Energy Agency. The reference air kerma rates were measured using a reference ionization chamber calibrated by the N-80 quality X-ray calibration field of the national metrology standard in Japan and with a correction to account for differences in photon energy due to the calibration field. Conversion coefficients for the 241Am γ-ray calibration field, including those not listed in the ISO 4037 standard series, were calculated based on the measured γ-ray fluence rate spectra.

Evaluation of radiation leakage in X-ray security inspection machine using a CZT spectrometer

Leakage radiation from X-ray security inspection machines is important, and measurement based on ionization chamber or scintillator detector is widely used. The leakage radiation is closely related to the size and the passing time of the luggage, the lead equivalent, the opening angle of the lead curtain, and the response time of the measuring instrument. To characterize the distribution of leakage radiation from the X-ray security inspection machine accurately, a small-volume CZT(CdZnTe) spectrometer was used to measure the energy spectra at a distance of 5 cm from the surface of the inspection machine. By designing and controlling the opening angle of the lead curtain according to the size of the luggage passing through the entrance and exit, the radiation dose was determined based on the measured energy spectra combined with the G(E)-function method. The results show that the maximum relative deviation between the air kerma rate and the ambient dose equivalent rate calculated by the G(E) function method with the standard dose rate does not exceed ±5%. The maximum relative deviation of the dose rate linear verification in the 137Cs radiation field is less than 2.5%. A calibrated CZT detector was utilized to measure the radiation leakage on the surface of the X-ray security inspection machine. It was discovered that the presence of the luggage items and the opening angle of the lead curtain will increase the leakage radiation dose on the surface of the security inspection machine system. This study provides a new approach for measuring scattered radiation of X-ray security inspection machines.

Parameters of ISO 4037 wide spectrum X-ray reference field

The parameters of the ISO-4037 wide spectrum (W-series) X-ray reference fields were simulated using the SpekPy web-based simulation software. One of the most important physical quantities (air Kerma rate) and other radiation quantities (X-ray fluence spectrum and its averaged energy, the first and the second half value layers, as well as the beam homogeneity coefficient) were also deduced. The comparison in radiation quantities between the simulated (obtained from this work) and the ISO-published data was performed to confirm the reliability of SpekPy simulations (the maximum discrepancy between them was less than 4.0%). The air Kerma rate trend as a function of the W-series X-ray reference field was investigated and presented in this work. The values of air Kerma rates can be applied in calibrations of wide-spectrum X-ray measuring devices.

Calibration system correction factor for measuring the reference air kerma rate (RAKR) applied to high dose rate 192Ir sources (HDR)

The aim of this study was to use computer simulation to analyze the impact of the aluminum fixing support on the Reference Air Kerma (RAK), a physical quantity obtained in a calibration system that was experimentally developed in the Laboratory of Radiological Sciences of the University of the State of Rio de Janeiro (LCR-UERJ). Correction factors due to scattered radiation and the geometry of the 192Ir sources were also sought to be determined. The computational simulation was validated by comparing some parameters of the experimental results with the computational results. These parameters were: verification of the inverse square law of distance, determination of (RAKR), analysis of the source spectrum with and without encapsulation, and the sensitivity curve of the Sourcecheck 4PI ionization chamber response, as a function of the distance from the source along the axial axis, using the microSelectron-v2 (mSv2) and GammaMedplus (GMp) sources. Kerma was determined by activity in the Reference air, with calculated values of 1.725 × 10−3 U. Bq−1 and 1.710 × 10−3 U. Bq−1 for the ionization chamber NE 2571 and TN 30001, respectively. The expanded uncertainty for these values was 0.932% and 0.919%, respectively, for a coverage factor (k = 2). The correction factor due to the influence of the aluminum fixing support for measurements at 1 cm and 10 cm from the source was 0.978 and 0.969, respectively. The geometric correction factor of the sources was ksg = 1.005 with an expanded uncertainty of 0.7% for a coverage factor (k = 2). This value has a difference of approximately 0.2% compared to the experimental values.

ISO 4037 narrow spectrum X-ray reference field: Simulation and measurement

The paper presents the characteristics of the ISO-4037 narrow spectrum X-ray reference fields in 02 different manners: simulation using the SpekPy and measurement using a calibrated ionization chamber. The physical (air Kerma rate) and radiation (X-ray fluence-spectrum-averaged energy, the first and the second half value layers, as well as the beam homogeneity coefficient) quantities were simulated using the SpekPy web-based simulation toolkit. In addition, air Kerma rates were measured by the ionization chamber. The characteristics of the ISO-4037 narrow spectrum X-ray reference fields were determined for various X-ray beam qualities (i.e., N-40, 60, 80, 100, 120, and 150) at 250 cm from the X-ray focal spot. The air Kerma rate tendency was deduced by comparing simulation and measurement data. The combined standard uncertainty of measured air Kerma rate was investigated and presented.

Application of unmanned aerial vehicles in emergency radiation monitoring

The paper is based on experiments within a project to prepare tutorial tasks on a training centre for testing radiation detectors fixed on unmanned aerial vehicles (UAVs) and in unmanned ground vehicles. The paper reports on a small UAV with NaI(Tl) 2“ x 2” detector for radiation monitoring in an emergency event and for radioactive source chasing and detection. The paper is focused on some special cases with the possibility to determine local air kerma rates and the activities of point sources. The detector was calibrated for air kerma rates from 5 nGy h−1 to 20 μGy h−1. The verified model of the NaI(Tl) 2″ x 2″ detector including the electronic module assembled on a UAV was designed in a Monte Carlo simulation. The model was used for calculating the air kerma rates at various altitudes above the ground both for a natural background and for selected point sources. The response functions for 137Cs, 131I, 192Ir, 60Co and 99Mo point sources were calculated by the Monte Carlo simulation to estimate their activities. Experiments were carried out with an NaI(Tl) 2“ x 2” detector fixed on a Robodrone UAV and flying over 60Co and 137Cs point sources over the airfield area and the local air kerma rates and the activities of the point sources were calculated with the AGAMA post-processing program. In addition, the response functions for 137Cs distributed uniformly on the surface were calculated by Monte Carlo simulation for future emergency purposes. The detection limits of selected man-made nuclides (point sources) were calculated.

Physician scatter dose in interventional CT fluoroscopy

AbstractPurposeTo quantify operator dose in interventional CT fluoroscopy (CTF) procedures and compare to catheterization laboratory and interventional radiology procedures.MethodsFifteen studies quantifying operator scatter dose for c‐arm fluoroscopy and CTF were reviewed from a literature survey. The dose provided in each study was normalized to skin entrance air kerma and air kerma rate including backscatter. The average air kerma rate and exposure duration were calculated and compared between c‐arm fluoroscopy and CTF. To enable operator scatter dose calculations in CTF procedures, a model was created which scaled the dose from a reference condition.ResultsOur literature survey indicated that for CTF relative to c‐arm fluoroscopy: (1) the mean air kerma rate is 3.5 times higher, while (2) the mean exposure duration is 31.6 times lower. On average, a physician would have to perform 9.1 times (i.e., 31.6/3.5) more CTF procedures relative to c‐arm fluoroscopy procedure to receive equal operator scatter doses. Our own experimental measurements provided scaling factors allowing physician scatter dose to be obtained at any rotation time, tube current, beam collimation, or beam energy.ConclusionOur results shed light onto a currently mis‐understood issue in radiology. Namely, that physicians receive more dose from CT relative to c‐arm fluoroscopy motivating them to retreat from the room during interventional exposures. Our literature review and experimental measurements indicate the opposite it true; interventional CT produces on average nine times less physician dose relative to c‐arm procedures. Our method allows for prospective/retrospective determination of an individual's dose.

Image Quality and Radiation Exposure in Abdominal Angiography: A Head-to-Head Comparison of Conventional Detector-Dose-Driven Versus Contrast-to-Noise Ratio-Driven Exposure Control at Various Source-to-Image Receptor Distances and Collimations in a Pilot Phantom and Animal Study.

This phantom and animal pilot study aimed to compare image quality and radiation exposure between detector-dose-driven exposure control (DEC) and contrast-to-noise ratio (CNR)-driven exposure control (CEC) as functions of source-to-image receptor distance (SID) and collimation. First, an iron foil simulated a guide wire in a stack of polymethyl methacrylate and aluminum plates representing patient thicknesses of 15, 25, and 35 cm. Fluoroscopic images were acquired using 5 SIDs ranging from 100 to 130 cm and 2 collimations (full field of view, collimated field of view: 6 × 6 cm). The iron foil CNRs were calculated, and radiation doses in terms of air kerma rate were obtained and assessed using a multivariate regression. Second, 5 angiographic scenarios were created in 2 anesthetized pigs. Fluoroscopic images were acquired at 2 SIDs (110 and 130 cm) and both collimations. Two blinded experienced readers compared image quality to the reference image using full field of view at an SID of 110 cm. Air kerma rate was obtained and compared using t tests. Using DEC, both CNR and air kerma rate increased significantly at longer SID and collimation below the air kerma rate limit. When using CEC, CNR was significantly less dependent of SID, collimation, and patient thickness. Air kerma rate decreased at longer SID and tighter collimation. After reaching the air kerma rate limit, CEC behaved similarly to DEC. In the animal study using DEC, image quality and air kerma rate increased with longer SID and collimation ( P < 0.005). Using CEC, image quality was not significantly different than using longer SID or tighter collimation. Air kerma rate was not significantly different at longer SID but lower using collimation ( P = 0.012). CEC maintains the image quality with varying SID and collimation stricter than DEC, does not increase the air kerma rate at longer SID and reduces it with tighter collimation. After reaching the air kerma rate limit, CEC and DEC perform similarly.

Monte Carlo simulation of air kerma rate constants for different radionuclides

The air kerma rate constant values for different radionuclides are often used in radiation shielding calculations, calibration of instruments, estimating the absorbed dose from brachytherapy sources, etc. Usually, air kerma rate constant values are calculated in a deterministic way. This work evaluates the possibility of air kerma rate constant estimation through Monte Carlo simulations. Ten different radionuclides were considered in this preliminary study, covering low and high-energy gamma spectra. Mean percentage differences of less than 10% relative to the results of reference works were found. Most of our results present less than a 5% relative percentage difference considering the literature results. The air kerma rate constants calculated in this work agree with reference results, thus validating the methodology, the photon spectra database used, and the Monte Carlo simulations with EGSnrc. Future work can extend the calculation of air kerma rate constants for other radionuclides and study the influence of different sources of uncertainty in its results.

Characteristics of the reference X-ray narrow-spectrum series at SSDL of Institute for Nuclear Science and Technology

This paper presents the characteristics of the reference X-ray narrow-spectrum series used in the Secondary Standard Dosimetry Laboratory (SSDL) at Institute for Nuclear Science and Technology (INST) with X-ray beam irradiator. In order to perform calibration works, it is highly important to verify the characteristics and qualities of reference X-ray beam recommended by the International Standardization Organization (ISO) 4037:2019. The characteristics of the X-ray beams in terms of the half-value layer, homogeneity coefficient and the air kerma rate are determined for the narrow-spectrum series in the 40 and 150 keV range. The related dosimetric quantities such as the ambient dose equivalent and personal dose equivalent also determined. The experimental values are well consistent with the recommended values of the ISO 4037 criteria. It implies that the reference X-ray narrow-spectrum series (N-series) can be applied in calibration works of X-ray measuring devices used in radiation safety assessment.

Evaluating delivered radiation dose in intraoperative radiotherapy for breast cancer using TLD

The extra radiation that it delivers has been questioned by patients, physicians, and the public for early breast cancer patients of intraoperative radiotherapy (IORT). This investigation concerns a left breast Rando phantom with a lumpectomy cavity of 30 cm3 of left breast of Rando phantom made of polymethylmethacrylate (PMMA). Thermoluminescent dosimetry (TLD) was used to evaluate the extra radiation dose or air kerma (kair) rate under IORT from 20 Gy, 50 kV of an Xoft Axxent system. TLDs were first calibrated using 50 kV photons, and then inserted at phantom positions that were close to the positions of the represented organs and tissues. Equivalent doses (DT) delivered to the organ at risks (OAR) were evaluated according to ICRP 103. Entrance surface doses (ESD) or skin doses (Dskin) varied markedly among positions close to the lumpectomy cavity. The dose was 20 Gy at the surface of a balloon applicator and kair varied from 6.40 ± 0.92 Gy down to 1.20 ± 0.30 mGy along the left-right axis of the 17th slice of Rando. These experimental results are compared with those in the literature. The shielding effect of the tungsten-impregnated rubber was also evaluated. This study supports recommendations to patients, relatives, physicians and radiologists concerning IORT.

Air kerma reference field with high energy photons using a 15 MeV electron beam from a clinical linear accelerator.

In the medical and nuclear fields, there are environments where exposure to photons with energies above several MeV can result in problems. The National Metrology Institute of Japan has developed a high-energy photon field using a 15 MeV electron beam of a clinical linear accelerator with a copper target and an aluminium filter unit to facilitate dosimeter calibration in terms of air kerma. To determine the air kerma rate, the energy fluence distribution at a reference point was calculated, and both calculations and experiments evaluated the effective energy and spatial dose distribution. Moreover, to validate the air kerma measurement, two commercial cavity chambers were calibrated in a developed photon field. The results obtained exhibited a 4% difference compared with those in a Co-60γ-ray reference field.

Key comparison BIPM.RI(I)-K8 of high dose-rate 192Ir brachytherapy standards for reference air kerma rate of the LNE-LNHB and the BIPM

Main textAn indirect comparison of the standards for reference air kerma rate for 192Ir high dose rate (HDR) brachytherapy sources of the Laboratoire National Henri Becquerel (LNE-LNHB), France, and of the Bureau International des Poids et Mesures (BIPM) was carried out at the LNE-LNHB in May 2024. The comparison result, based on the calibration coefficients for a transfer standard and expressed as a ratio of the LNE-LNHB and the BIPM standards for reference air kerma rate, is 0.9990 with a combined standard uncertainty of 0.0071.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K8 of high dose-rate 192Ir brachytherapy standards for reference air kerma rate of the PTB and the BIPM

Main textAn indirect comparison of the standards for reference air kerma rate for 192Ir high dose rate (HDR) brachytherapy sources of the Physikalisch-Technische Bundesanstalt (PTB), Germany, and of the Bureau International des Poids et Mesures (BIPM) was carried out at the PTB in May 2023. The comparison result, based on the calibration coefficients for a transfer standard and expressed as a ratio of the PTB and the BIPM standards for reference air kerma rate, is 1.0022 with a combined standard uncertainty of 0.0101.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K8 of high dose-rate 192Ir brachytherapy standards for reference air kerma rate of the VSL and the BIPM

Main textA new key comparison of the standards for reference air kerma rate for 192Ir high dose rate (HDR) brachytherapy sources of the Dutch Metrology Institute (VSL), The Netherlands, and the Bureau International des Poids et Mesures (BIPM) was carried out at the VSL in May 2019. The comparison result, based on the calibration coefficients for a transfer standard and expressed as a ratio of the VSL and the BIPM standards for reference air kerma rate, is 0.9926 with a combined standard uncertainty of 0.0055.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Establishment of Hp(3) calibration system for eye dose monitoring in Taiwan.

In response to the ICRP's amending the occupational exposure limit for the eye lens, the Institute of Nuclear Energy Research (INER) established the Hp(3) calibration system for eye dose monitoring in Taiwan to accurately assess the dose received in the eye lens. INER employed the narrow-spectrum series radiation according to the ISO 4037 as the X-ray radiation qualities, and the measured half-value layer consistent with a 5% difference. The air kerma rate standard was determined by the self-made free air chamber, and through dose conversion coefficient referring to ISO 4037 to obtain the Hp(3) on an ISO cylinder phantom. Furthermore, the calibration system was provided as the characteristics tests for DOSIRIS headset dosemeters. Finally, the Hp(3) calibration system has been established in Taiwan, and it can be used to provide calibration services for eye lens dosemeters and be applied to the proficiency testing that will be held in 2023.

Effect of shape of automatic dose rate control and wedge compensation filter on radiation dose in an angiography system with a flat-panel detector.

The purpose was to investigate air-kerma area product (PKA) and entrance surface air-kerma rate ([Formula: see text]a,e) on the effect of the shape of automatic dose rate control (ADRC) in the presence of a wedge compensation filter. We compared and evaluated the variability of the X-ray output using a combination of wedge compensation filters and the ADRC. Two ADRC shapes (round and square) and three poly-methyl-methacrylate thicknesses (15, 20, and 25cm) were used. A wedge compensation filter was inserted 2cm at a time, up to 6cm. When the wedge compensation filter was inserted to 6 cm for 20cm of poly-methyl-methacrylate, the X-ray output fluctuated significantly. The PKA was reduced by 39% when the wedge compensation filter was inserted to 6 cm and by 59% when it was inserted to 4cm under round-type for 20cm poly-methyl-methacrylate. The shape of the ADRC affects [Formula: see text]a,e and PKA.

Limiting Exposure to Scattered Radiation From a CT System Installed ina Two-Sided Deployable ISO-Shelter.

Diagnostic radiology in the deployed military environment (in-theater diagnostic radiology) was greatly improved in the early 1990s with the addition of CT systems installed in military-grade one-sided expandable ISO-shelters. These shelters were provided with limited radiation shielding by several flexible lead curtains covering only a small portion of the shelter walls, necessitating placement of deployed CT systems at substantial distances from the field medical facility to limit exposures to personnel from secondary radiation. The newest generation deployable CT system is housed in a two-sided ISO-shelter with radiation shielding applied to the shelter walls. To ensure compliance with military and national standards for protection against ionizing radiation, we developed a simple method to calculate safe distances based on workload, frequencies of the various CT exams performed, and occupancy of controlled and uncontrolled areas. Calculation of radiation air kerma rates outside a two-sided CT ISO-shelter was developed using guidance from the National Council on Radiation Protection and Measurements Report No. 147. The simplified formula included measured radiation transmission factors for the ISO-shelter wall and installed shielding, occupancy factors, fraction of all CT exams that covered the chest, abdomen, and/or pelvis, total number of CT exams per week, and shielding design goals for controlled and uncontrolled areas. The formula was modified subsequently to account for whole-body CT exams expected during armed conflict. Calculated safe distances revealed that the shielded two-sided CT ISO-shelter can be positioned much closer to the surgical shelters of the field medical unit than the previously unshielded one-sided CT ISO-shelter. Tables of safe distances for controlled and uncontrolled areas for the two medical support environments of disaster relief/peacekeeping and combat are provided. For example, for a controlled area at 100% occupancy when 300 CT exams per week are performed and 50% of those exams are of the chest, abdomen, and/or pelvis, the safe distance between the nearest surgical shelter and the shielded CT ISO-shelter is 2.1m. By comparison, the safe distance for an unshielded CT ISO-shelter is 8.5 m under the same conditions. For lower occupancy factors and lower weekly workload, safe distances from the nearest surgical shelter are often negligible. The shielding in the new deployable CT ISO-shelter substantially reduces the distance between it and the surgical shelters of the field medical unit necessary to ensure radiation safety. Safe distances depend on several factors including workload, types and frequencies of CT exams, occupancy factors, and classification of the area around the ISO-shelter, i.e., controlled and uncontrolled.