Recommendations for the use of active personal dosemeters (APDs) in interventional workplaces in hospitals.

Occupational radiation doses from interventional procedures have the potential to be relatively high. The requirement to optimise these doses encourages the use of electronic or active personal dosimeters (APDs) which are now increasingly used in hospitals. They are typically used in tandem with a routine passive dosimetry monitoring programme, with APDs used for real-time readings, for training purposes and when new imaging technology is introduced. However, there are limitations when using APDs. A survey in hospitals to identify issues related to the use of APDs was recently completed, along with an extensive series of APD tests by the EURADOS Working Group 12 on Dosimetry for Medical Imaging. The aim of this review paper is to summarise the state of the art regarding the use of APDs. We also used the results of our survey and our tests to develop a set of recommendations for the use of APDs in the clinical interventional radiology/cardiology settings, and draw attention to some of the current challenges.

PATIENT-SPECIFIC DOSE ESTIMATES IN DYNAMIC COMPUTED TOMOGRAPHY MYOCARDIAL PERFUSION EXAMINATION.

The study aimed to implement realistic source models of a computed tomography (CT) scanner and Monte Carlo simulations to actual patient data and to calculate patient-specific organ and effective dose estimates for patients undergoing dynamic CT myocardial perfusion examinations. Source models including bowtie filter, tube output and x-ray spectra were determined for a dual-source Siemens Somatom Definition Flash scanner. Twenty CT angiography patient datasets were merged with a scaled International Commission on Radiological Protection (ICRP) 110 voxel phantom. Dose simulations were conducted with ImpactMC software. Effective dose estimates varied from 5.0 to 14.6 mSv for the 80 kV spectrum and from 8.9 to 24.7 mSv for the 100 kV spectrum. Significant differences in organ doses and effective doses between patients emphasise the need to use actual patient data merged with matched anthropomorphic anatomy in the dose simulations to achieve a reasonable level of accuracy in the dose estimation procedure.

ESTIMATION OF HP(3) AMONG STAFF MEMBERS IN TWO NUCLEAR MEDICINE UNITS IN FINLAND.

The eye lens exposure among 16 technicians in two nuclear medicine departments at university hospitals in Finland was investigated by measuring the operational quantity Hp(3) using EYE-D dosemeters. For all workers, the annual mean Hp(3) was estimated to be 1.1 mSv (max. 3.9 mSv). The relation between Hp(3) to routinely monitored personal dose equivalent Hp(10) was clearly correlated. Considering individual dose measurement periods (2-4 weeks), the Hp(3)/Hp(10) ratio was 0.7 (Pearson's coefficient r = 0.90, p < 0.001, variation of ratio 0.1-2.3). The variation decreased considerably with increasing Hp(10) (σ2 = 0.04 vs. 0.43 for Hp(10) > 0.1 mSv vs. < 0.1 mSv, respectively), i.e. higher Hp(10) predicts Hp(3) more reliably. Moreover, annual Hp(10) data from national dose register during 2009-2018 were used to derive the annual Hp(3) applying the Hp(3)/Hp(10) ratio. The data from Finnish nuclear medicine departments imply that routine measurements of Hp(3) among nuclear medicine technicians are not justified.

Calculated beam quality correction factors for ionization chambers in MV photon beams.

The beam quality correction factor, [Formula: see text], which corrects for the difference in the ionization chamber response between the reference and clinical beam quality, is an integral part of radiation therapy dosimetry. The uncertainty of [Formula: see text] is one of the most significant sources of uncertainty in the dose determination. To improve the accuracy of available [Formula: see text] data, four partners calculated [Formula: see text] factors for 10 ionization chamber models in linear accelerator beams with accelerator voltages ranging from 6 MV to 25 MV, including flattening-filter-free (FFF) beams. The software used in the calculations were EGSnrc and PENELOPE, and the ICRU report 90 cross section data for water and graphite were included in the simulations. Volume averaging correction factors were calculated to correct for the dose averaging in the chamber cavities. A comparison calculation between partners showed a good agreement, as did comparison with literature. The [Formula: see text] values from TRS-398 were higher than our values for each chamber where data was available. The [Formula: see text] values for the FFF beams did not follow the same [Formula: see text], [Formula: see text] relation as beams with flattening filter (values for 10 MV FFF beams were below fits made to other data on average by 0.3%), although our FFF sources were only for Varian linacs.

CT beam dosimetric characterization procedure for personalized dosimetry.

Personalized dosimetry in computed tomography (CT) can be realized by a full Monte Carlo (MC) simulation of the scan procedure. Essential input data needed for the simulation are appropriate CT x-ray source models and a model of the patient's body which is based on the CT image. The purpose of this work is to develop comprehensive procedures for the determination of CT x-ray source models and their verification by comparison of calculated and measured dose distributions in physical phantoms. Mobile equipment together with customized software was developed and used for non-invasive determination of equivalent source models of CT scanners under clinical conditions. Standard and physical anthropomorphic CT dose phantoms equipped with real-time CT dose probes at five representative positions were scanned. The accumulated dose was measured during the scan at the five positions. ImpactMC, an MC-based CT dose software program, was used to simulate the scan. The necessary inputs were obtained from the scan parameters, from the equivalent source models and from the material-segmented CT images of the phantoms. 3D dose distributions in the phantoms were simulated and the dose values calculated at the five positions inside the phantom were compared to measured dose values. Initial results were obtained by means of a General Electric Optima CT 660 and a Toshiba (Canon) Aquilion ONE. In general, the measured and calculated dose values were within relative uncertainties that had been estimated to be less than 10%. The procedures developed were found to be viable and rapid. The procedures are applicable to any scanner type under clinical conditions without making use of the service mode with stationary x-ray tube position. Results show that the procedures are well suited for determining and verifying the equivalent source models needed for personalized CT dosimetry based on post-scan MC calculations.

Establishing the European diagnostic reference levels for interventional cardiology.

Interventional cardiac procedures may be associated with high patient doses and therefore require special attention to protect the patients from radiation injuries such as skin erythema, cardiovascular tissue reactions or radiation-induced cancer. In this study, patient exposure data is collected from 13 countries (37 clinics and nearly 50 interventional rooms) and for 10 different procedures. Dose data was collected from a total of 14,922 interventional cardiology procedures. Based on these data European diagnostic reference levels (DRL) for air kerma-area product are suggested for coronary angiography (CA, DRL = 35 Gy cm2), percutaneous coronary intervention (PCI, 85 Gy cm2), transcatheter aortic valve implantation (TAVI, 130 Gy cm2), electrophysiological procedures (12 Gy cm2) and pacemaker implantations. Pacemaker implantations were further divided into single-chamber (2.5 Gy cm2) and dual chamber (3.5 Gy cm2) procedures and implantations of cardiac resynchronization therapy pacemaker (18 Gy cm2). Results show that relatively new techniques such as TAVI and treatment of chronic total occlusion (CTO) often produce relatively high doses, and thus emphasises the need for use of an optimization tool such as DRL to assist in reducing patient exposure. The generic DRL presented here facilitate comparison of patient exposure in interventional cardiology.

CALIBRATION AND USE OF A PENCIL-TYPE CT CHAMBER: EFFECT OF THE PMMA BODY PHANTOM.

A pencil-type ionization chamber commonly used in computed tomography (CT) dosimetry is usually calibrated free in air, but used inside a PMMA CT phantom. Measurements and Monte Carlo simulations are used to investigate the validity of chamber calibration in this situation where the body phantom modifies the x-ray spectrum impinging on the chamber. The results for the PTW 30009 chamber indicate that the additional uncertainty in CT dose index (CTDIw) measurement introduced by the phantom is ~1% or less. The pencil chamber used in CTDIw measurements should have a flat energy response down to at least 30 keV photon energy to avoid excessive increase in measurement uncertainty.

Characterisation of grids of point detectors in maximum skin dose measurement in fluoroscopically-guided interventional procedures.

PURPOSE: Point detectors are frequently used to measure patient's maximum skin dose (MSD) in fluoroscopically-guided interventional procedures (IP). However, their performance and ability to detect the actual MSD are rarely evaluated. The present study investigates the sampling uncertainty associated with the use of grids of point detectors to measure MSD in IP. METHOD: Chemoembolisation of the liver (CE), percutaneous coronary intervention (PCI) and neuroembolisation (NE) procedures were studied. Spatial dose distributions were measured with XR-RV3 Gafchromic(®) films for 176 procedures. These distributions were used to simulate measurements performed using grids of detectors such as thermoluminescence detectors, with detector spacing from 1.4 up to 10 cm. RESULTS: The sampling uncertainty was the highest in PCI and NE procedures. With 40 detectors covering the film area (36 cm × 44 cm), the maximum dose would be on average 86% and 63% of the MSD measured with Gafchromic(®) films in CE and PCI procedures, respectively. In NE procedures, with 27 detectors covering the film area (14 cm × 35 cm), the maximum dose measured would be on average 82% of the MSD obtained with the Gafchromic(®) films. CONCLUSION: Thermoluminescence detectors show good energy and dose response in clinical beam qualities. However the poor spatial resolution of such point-like dosimeters may far outweigh their good dosimetric properties. The uncertainty from the sampling procedure should be estimated when point detectors are used in IP because it may lead to strong underestimation of the MSD.

Characterization of XR-RV3 GafChromic(®) films in standard laboratory and in clinical conditions and means to evaluate uncertainties and reduce errors.

PURPOSE: To investigate the optimal use of XR-RV3 GafChromic(®) films to assess patient skin dose in interventional radiology while addressing the means to reduce uncertainties in dose assessment. METHODS: XR-Type R GafChromic films have been shown to represent the most efficient and suitable solution to determine patient skin dose in interventional procedures. As film dosimetry can be associated with high uncertainty, this paper presents the EURADOS WG 12 initiative to carry out a comprehensive study of film characteristics with a multisite approach. The considered sources of uncertainties include scanner, film, and fitting-related errors. The work focused on studying film behavior with clinical high-dose-rate pulsed beams (previously unavailable in the literature) together with reference standard laboratory beams. RESULTS: First, the performance analysis of six different scanner models has shown that scan uniformity perpendicular to the lamp motion axis and that long term stability are the main sources of scanner-related uncertainties. These could induce errors of up to 7% on the film readings unless regularly checked and corrected. Typically, scan uniformity correction matrices and reading normalization to the scanner-specific and daily background reading should be done. In addition, the analysis on multiple film batches has shown that XR-RV3 films have generally good uniformity within one batch (<1.5%), require 24 h to stabilize after the irradiation and their response is roughly independent of dose rate (<5%). However, XR-RV3 films showed large variations (up to 15%) with radiation quality both in standard laboratory and in clinical conditions. As such, and prior to conducting patient skin dose measurements, it is mandatory to choose the appropriate calibration beam quality depending on the characteristics of the x-ray systems that will be used clinically. In addition, yellow side film irradiations should be preferentially used since they showed a lower dependence on beam parameters compared to white side film irradiations. Finally, among the six different fit equations tested in this work, typically used third order polynomials and more rational and simplistic equations, of the form dose inversely proportional to pixel value, were both found to provide satisfactory results. Fitting-related uncertainty was clearly identified as a major contributor to the overall film dosimetry uncertainty with up to 40% error on the dose estimate. CONCLUSIONS: The overall uncertainty associated with the use of XR-RV3 films to determine skin dose in the interventional environment can realistically be estimated to be around 20% (k = 1). This uncertainty can be reduced to within 5% if carefully monitoring scanner, film, and fitting-related errors or it can easily increase to over 40% if minimal care is not taken. This work demonstrates the importance of appropriate calibration, reading, fitting, and other film-related and scan-related processes, which will help improve the accuracy of skin dose measurements in interventional procedures.

Measurement of maximum skin dose in interventional radiology and cardiology and challenges in the set-up of European alert thresholds.

To help operators acknowledge patient dose during interventional procedures, EURADOS WG-12 focused on measuring patient skin dose using XR-RV3 gafchromic films, thermoluminescent detector (TLD) pellets or 2D TL foils and on investigating possible correlation to the on-line dose indicators such as fluoroscopy time, Kerma-area product (KAP) and cumulative air Kerma at reference point (CK). The study aims at defining non-centre-specific European alert thresholds for skin dose in three interventional procedures: chemoembolization of the liver (CE), neuroembolization (NE) and percutaneous coronary interventions (PCI). Skin dose values of >3 Gy (ICRP threshold for skin injuries) were indeed measured in these procedures confirming the need for dose indicators that correlate with maximum skin dose (MSD). However, although MSD showed fairly good correlation with KAP and CK, several limitations were identified challenging the set-up of non-centre-specific European alert thresholds. This paper presents preliminary results of this wide European measurement campaign and focuses on the main challenges in the definition of European alert thresholds.

Detection of fast neutrons from shielded nuclear materials using a semiconductor alpha detector.

The response of a semiconductor alpha detector to fast (>1 MeV) neutrons was investigated by using measurements and simulations. A polyethylene converter was placed in front of the detector to register recoil protons generated by elastic collisions between neutrons and hydrogen nuclei of the converter. The developed prototype equipment was tested with shielded radiation sources. The low background of the detector and insensitivity to high-energy gamma rays above 1 MeV are advantages when the detection of neutron-emitting nuclear materials is of importance. In the case of a (252)Cf neutron spectrum, the intrinsic efficiency of fast neutron detection was determined to be 2.5×10(-4), whereas three-fold greater efficiency was obtained for a (241)AmBe neutron spectrum.

Determination of 239Pu/240Pu isotopic ratio by high-resolution alpha-particle spectrometry using the ADAM program.

A novel analysis program to unfold alpha-particle energy spectra was introduced, demonstrated and validated using radiochemically processed test sources, which contained different amounts of (239)Pu and (240)Pu. A high-resolution alpha spectrometer was used for data acquisition. The software known as ADAM unfolds the spectra using nuclide-specific decay data as a constraint. The peaks can have different shapes and the software can also cope with the coincidences between alpha particles and electrons/photons. In the present paper, the (239)Pu/(240)Pu activity ratios from alpha spectrometry agreed, within the stated uncertainties, with the reference values. Number of counts in the (239,240)Pu peak group must be larger than 100 to obtain reliable values when using semiconductor detector of energy resolution FWHM=10.6 keV.

Energy loss measurement of protons in liquid water.

The proton stopping power of liquid water was, for the first time, measured in the energy range 4.7-15.2 MeV. The proton energies were determined by the time-of-flight transmission technique with the microchannel plate detectors, which were especially developed for timing applications. The results are compared to the literature values (from ICRU Report 49 (1993) and Janni's tabulation (1982 At. Data Nucl. Data Tables 27 147-339)) which are based on Bethe's formula and an agreement is found within the experimental uncertainty of 4.6%. Thus, earlier reported discrepancy between the experimental and literature stopping power values at lower energies was not observed at the energies considered in this experiment.

Weighting of secondary radiations in organ dose calculations.

The current system of dose quantities in radiological protection is based, in addition to the absorbed dose, on the concepts of equivalent dose and effective dose. This system has been developed mainly with uniform whole-body exposures in mind. Conceptual and practical problems arise when the system is applied to more general exposure situations where the radiation quality is altered within the human body. In this article these problems are discussed, using proton beam radiotherapy as a specific example, and a proposition is made that dose equivalent quantities should be used instead of equivalent doses when organ doses are of interest. The calculations of out-of-field organ doses in proton therapy show that the International Commission on Radiological Protection-prescribed use of the proton weighting factor generally leads to an underestimation of the stochastic risks, while the use of neutron weighting factors in the way as practised in the literature leads to a significant overestimation of these risks.

Characterization of radioactive particles using non-destructive alpha spectrometry.

Spherical particles with known properties were used to demonstrate and test a novel software package known as AASIFIT, which is able to unfold complex alpha spectra. A unique feature of the program is that it uses simulated peak shapes in the fitting process. The experimental reference particles in the testing were artificially produced U particles of diameter 1.4microm and a nuclear bomb particle with a twenty-fold greater diameter, mainly composed of U and Pu dioxides. AASIFIT was used to determine the density of the U particles. In addition, the activities of (239+240)Pu and (241)Am were determined for the nuclear bomb particle and compared to earlier determinations in the literature. The results of this investigation demonstrated that the software can be used to estimate the properties of particles emitting alpha radiation. However, the composition and geometry of the investigated particles need to be known with good accuracy for reliable estimates. Furthermore, uncertainties in the stopping power data, especially for U and Pu, may have an influence on the results obtained from the software.

Excitation functions of proton-induced reactions in (nat)Cu in the energy range 7-17 MeV.

Elemental production cross sections were measured for (p,x) reactions on natural Cu targets, leading to the formation of (62,63,65)Zn. These reactions are generally used for monitoring the proton beam intensity and energy e.g. in isotope production facilities. Cross sections were obtained by activation of stacked foils and subsequent gamma spectroscopy. The production data for (62,63,65)Zn between 7 and 16.5 MeV proton energy are presented as well as comparisons with literature values. Good agreement with the evaluated values was found for most of the cross-section values.

The decay of 133mXe.

The decay of (133m)Xe has been re-measured using an electron-transporter spectrometer and a planar HPGe detector. The sample of (133m)Xe was produced by means of proton-induced fission using an ion-guide based on-line mass separator. The deduced K and L+M+... shell conversion coefficients, alpha(Kappa)=6.5(9) and alpha(L+M+...)=2.9(4), agree within the uncertainty limits with the theoretical values and remove the inconsistencies between the previous experimental studies of (133m)Xe.

Occupational radiation doses in interventional radiology: simulations.

In interventional radiology, occupational radiation doses can be high. Therefore, many authors have established conversion coefficients from the dose-area product data or from the personal dosemeter reading to the effective dose of the radiologist. These conversion coefficients are studied also in this work, with an emphasis on sensitivity of the results to changes in exposure conditions. Comparison to earlier works indicates that, for the exposure conditions examined in this work, all previous models discussed in this work overestimate the effective dose of the radiologist when a lead apron and a thyroid shield are used. Without the thyroid shield, underestimation may occur with some models.

Dose from slow negative muons.

Conversion coefficients from fluence to ambient dose equivalent, from fluence to maximum dose equivalent and quality factors for slow negative muons are examined in detail. Negative muons, when stopped, produce energetic photons, electrons and a variety of high-LET particles. Contribution from each particle type to the dose equivalent is calculated. The results show that for the high-LET particles the details of energy spectra and decay yields are important for accurate dose estimates. For slow negative muons the ambient dose equivalent does not always yield a conservative estimate for the protection quantities. Especially, the skin equivalent dose is strongly underestimated if the radiation-weighting factor of unity for slow muons is used. Comparisons to earlier studies are presented.

Direct high-resolution alpha spectrometry from nuclear fuel particles in an outdoor air sample.

The potential use of direct high-resolution alpha spectrometry to identify the presence of transactinium elements in air samples is illustrated in the case when alpha-particle-emitting radionuclides are incorporated in nuclear fuel particles. Alpha particle energy spectra are generated through Monte Carlo simulations assuming a nuclide composition similar to RBMK (Chernobyl) nuclear fuel. The major alpha-particle-emitting radionuclides, in terms of activity, are 242Cm, 239Pu and 240Pu. The characteristics of the alpha peaks are determined by fuel particle properties as well as the type of the air filter. It is shown that direct alpha spectrometry can be readily applied to membrane filter samples containing nuclear fuel particles when rapid nuclide identification is of relevance. However, the development of a novel spectrum analysis code is a prerequisite for unfolding complex alpha spectra.