First Latin American and Caribbean interlaboratory comparison exercise for SSDLs on reference irradiation capabilities in personal dose equivalent.

A comparison exercise of Latin American and Caribbean Secondary Standards Dosimetry Laboratories (SSDLs) was jointly organized by the International Atomic Energy Agency (IAEA) and the Ionizing Radiation Metrology Laboratory at the Federal University of Pernambuco (LMRI-DEN/UFPE). This exercise was organized during an IAEA regional meeting on the review and update of calibration capabilities in Latin America, held in Recife, during the period from 23 to 27 April 2018 under the technical cooperation project ME-RLA 9085-170572. Fifteen participating SSDLs were required to irradiate optically stimulated personal dosimeters in terms of the personal dose equivalent Hp(10) in137Cs radiation quality. In addition, the IAEA Dosimetry Laboratory in Seibersdorf, Austria, and the National Physical Laboratory in Teddington, Middlesex, UK participated in this exercise as reference institutes. Each participant received 10 dosimeters that were hand-carried directly to the SSDL. Two nominal dose values of 2 mSv and 4 mSv were selected for this exercise. The participants irradiated the dosimeters using the setup and the procedures which are normally used in their standard laboratory for Hp(10) dosimeter irradiations. The dosimeters were evaluated as they were received by the coordinating laboratory, using a single BeOSL Reader. The results show that, except for one laboratory, the differences between the dosimeter reading and the assigned values were within 10%; this is consistent with the expanded uncertainty. The results indicate that most of the participant laboratories have a good capability to irradiate personal dosimeters in the quantity Hp(10).

Implementation of a 23-h surgery model in a tertiary care hospital: a safe and feasible model with high patient satisfaction.

BACKGROUND: The 23-h surgery model consists of elective operative care with an overnight hospital stay for patients unsuitable for day case surgery. The aim of this study was to assess the success of the 23-h surgery model. METHODS: This was a prospective follow-up study of patients undergoing surgery with the planned 23-h model in a tertiary-care university hospital during a 12-month period 2 years after the model was implemented. Patients were interviewed 2 weeks after surgery, and the hospital operative database and patient records were searched. The primary outcome was the success of the process, defined as discharge before 10.00 hours on the first morning after surgery. Secondary outcomes were 30-day readmission and reoperation rates, adverse events, and patient satisfaction with the process. RESULTS: Between May 2017 and May 2018, 993 adult patients underwent surgery with the 23-h model, of whom 937 adhered to the model as planned (success rate 94·4 per cent). Gynaecological, gastrointestinal and orthopaedic surgery were the three most common surgical specialties. The surgical process was changed to an in-hospital model for 45 patients (4·5 per cent), and 11 (1·1 per cent) were discharged on the day of surgery. The readmission rate was 1·9 per cent (19 of 993), and five patients (0·5 per cent) had a reoperation within 30 days of surgery. Fifty-nine adverse events were noted in 53 patients (5·3 per cent), most commonly infection. Patient satisfaction was a median of 6-7 (maximum 7) points for various aspects of the model. CONCLUSION: The success rate and patient satisfaction for the 23-h surgery model was high.

ANTECEDENTES: El modelo de cirugía de 23 horas consiste en un procedimiento quirúrgico electivo con estancia en el hospital durante una noche en aquellos pacientes que no son adecuados para cirugía ambulatoria. MÉTODOS: Se puso en marcha un estudio prospectivo de seguimiento de pacientes sometidos a cirugía con un modelo planificado de 23 horas en un hospital universitario de tercer nivel durante un periodo de 12 meses a los dos años de la implementación del modelo. Los pacientes fueron entrevistados a las dos semanas tras la cirugía, y se realizaron búsquedas en las bases de datos operativas y en los informes de los pacientes. El resultado primario fue el éxito del proceso definido como el alta antes de las 10 horas en la primera mañana postoperatoria. Los resultados secundarios fueron el reingreso a los 30 días y la tasa de reoperaciones, eventos adversos, y satisfacción del paciente con el proceso. RESULTADOS: Entre mayo de 2017 y mayo de 2018, 993 pacientes adultos fueron sometidos a cirugía con un modelo planificado de 23 horas, de los cuales 937 pacientes siguieron el modelo tal como se planificó (tasa de éxito 94,4%). Las tres especialidades quirúrgicas más frecuentes fueron ginecología, aparato digestivo y ortopedia. El proceso quirúrgico se cambió a un modelo de hospitalización en 45 (4,5%) pacientes, y 11 (1,1%) pacientes fueron dados de alta en el día de la cirugía. La tasa de reingreso fue del 1,9% (n = 19) y 5 pacientes (0,5%) precisaron de una reoperación en los primeros 30 días tras la cirugía. Se observaron eventos adversos en 53 pacientes (5,3%), siendo una infección el más frecuente. La satisfacción del paciente tuvo una mediana de 6-7 (de un total de 7) puntos para varios aspectos del modelo. CONCLUSIÓN: La tasa de éxito y la satisfacción del paciente del modelo de cirugía de 23 horas son elevadas.

Moving beyond quality control in diagnostic radiology and the role of the clinically qualified medical physicist.

Quality control (QC), according to ISO definitions, represents the most basic level of quality. It is considered to be the snapshot of the performance or the characteristics of a product or service, in order to verify that it complies with the requirements. Although it is usually believed that "the role of medical physicists in Diagnostic Radiology is QC", this, not only limits the contribution of medical physicists, but is also no longer adequate to meet the needs of Diagnostic Radiology in terms of Quality. In order to assure quality practices more organized activities and efforts are required in the modern era of diagnostic radiology. The complete system of QC is just one element of a comprehensive quality assurance (QA) program that aims at ensuring that the requirements of quality of a product or service will consistently be fulfilled. A comprehensive Quality system, starts even before the procurement of any equipment, as the need analysis and the development of specifications are important components under the QA framework. Further expanding this framework of QA, a comprehensive Quality Management System can provide additional benefits to a Diagnostic Radiology service. Harmonized policies and procedures and elements such as mission statement or job descriptions can provide clarity and consistency in the services provided, enhancing the outcome and representing a solid platform for quality improvement. The International Atomic Energy Agency (IAEA) promotes this comprehensive quality approach in diagnostic imaging and especially supports the field of comprehensive clinical audits as a tool for quality improvement.

Incident air kerma to absorbed organ dose conversion factors for breast and lung in PA thorax radiography: The effect of patient thickness and radiation quality.

PURPOSE: Converting the measurable quantities to patient organ doses in projection radiography is usually based on a standard-sized patient model and a specific radiation quality, which are likely to differ from the real situation. Large inaccuracies can therefore be obtained in organ doses, because organ doses are dependent on the exposure parameters, exposure geometry and patient anatomy. In this study, the effect of radiation quality and patient thickness on the organ dose conversion factors were determined. METHODS: In this study, the posterior-anterior projection radiograph of the thorax was selected in order to determine the effect of radiation quality (tube voltages of 70-130kV and total filtrations of 3mmAl to 4mmAl+0.2 mmCu) and patient thickness (anterior-posterior thicknesses of 19.4-30.8cm) on the breast and lung dose conversion factors. For this purpose, Monte Carlo simulation programs ImpactMC and PCXMC were used with computed tomography examination data of adult male and female patients and mathematical hermaphrodite phantoms, respectively. RESULTS: Compared to the reference beam quality and patient thickness, the relative variation range in organ dose conversion factors was up to 74% for different radiation qualities and 122% for different patient thicknesses. CONCLUSIONS: Conversion factors should only be used with comprehensive understanding of the exposure conditions, considering the exposure parameters, exposure geometry and patient anatomy they are valid for. This study demonstrates that patient thickness-specific and radiation quality-specific conversion factors are needed in projection radiography.

Image quality in CT: From physical measurements to model observers.

Evaluation of image quality (IQ) in Computed Tomography (CT) is important to ensure that diagnostic questions are correctly answered, whilst keeping radiation dose to the patient as low as is reasonably possible. The assessment of individual aspects of IQ is already a key component of routine quality control of medical x-ray devices. These values together with standard dose indicators can be used to give rise to 'figures of merit' (FOM) to characterise the dose efficiency of the CT scanners operating in certain modes. The demand for clinically relevant IQ characterisation has naturally increased with the development of CT technology (detectors efficiency, image reconstruction and processing), resulting in the adaptation and evolution of assessment methods. The purpose of this review is to present the spectrum of various methods that have been used to characterise image quality in CT: from objective measurements of physical parameters to clinically task-based approaches (i.e. model observer (MO) approach) including pure human observer approach. When combined together with a dose indicator, a generalised dose efficiency index can be explored in a framework of system and patient dose optimisation. We will focus on the IQ methodologies that are required for dealing with standard reconstruction, but also for iterative reconstruction algorithms. With this concept the previously used FOM will be presented with a proposal to update them in order to make them relevant and up to date with technological progress. The MO that objectively assesses IQ for clinically relevant tasks represents the most promising method in terms of radiologist sensitivity performance and therefore of most relevance in the clinical environment.

Conformance of mean glandular dose from phantom and patient data in mammography.

In mammography dosimetry, phantoms are often used to represent breast tissue. The conformance of phantom- and patient-based mean glandular dose (MGD) estimates was evaluated mainly from the aspect of diagnostic reference levels. Patient and phantom exposure data were collected for eight diagnostic and three screening mammography devices. More extensive assessments were performed for two devices. The average breast thickness was close to the nationally used reference of 50 mm in diagnostic (50 mm, SD = 13 mm, n = 5342) and screening (47 mm, SD = 13 mm, n = 395) examinations. The average MGD for all breasts differed by 2% from the MGD determined for breasts in the limited compressed thickness range of 40-60 mm. The difference between phantom- and patient-based MGD estimations was up to 30%. Therefore, phantom measurements cannot replace patient dose data in MGD determination.

Patient exposure levels in radiotherapy CT simulations in Finland.

Computed tomography (CT)-based simulation is an essential part of the radiotherapy treatment process. Patient exposure levels in CT simulations were collected from 15 CT systems from all 13 Finnish radiation therapy centres. A large standard deviation up to 56 % in dose levels between CT systems was noticed. Average volumetric CT dose indexes (in body phantom) were 24, 18 and 29 mGy for prostate, resection breast and head and neck treatment targets, respectively, and 70 mGy (in head phantom) for whole brain. These average dose indexes were much higher than those in corresponding diagnostic imaging in Finland. Dose levels in simulations with some devices were even over 3-fold higher than the diagnostic reference level for the same area of interest. Moreover, large variations in other exposure parameters, such as pitch and slice thickness, were seen. The results were discussed nationally, and general guidance to optimise dose levels was shared.

Calibration and features of air-kerma length product meters.

Pencil-type air-kerma length product meters are generally used for quality control and radiation exposure measurements in computed tomography. To ensure reliable results, these meters should be calibrated so that measurements are traceable to international standards. Suitable calibration procedures, together with the properties of these meters, were examined and compared with the international standards and recommendations. The calibration procedure and setup used in this study were slightly modified compared with international recommendations. The special collimator system was found to cause less scatter than similar setups in earlier studies. The energy dependence of the meter response was investigated for several types of meters with standard radiation qualities. With most tested meter types, the total variation due to energy dependence was <4 %, but some had strong energy dependence and the variation was up to 15 % or higher. This highlights the importance of a proper calibration. The response of one semiconductor meter type varied up to 8 % when rotating the meter around its axis; this should be taken into account when making calibrations with a static setup.

Determining air kerma from pixel values in digital mammography.

The pixels in digital detectors used in x-ray imaging can be considered as small dose meters. In mammography, the image detector area is commonly only partly covered by tissue and the incident air kerma could be monitored by using pixel values from the detector elements in the unattenuated primary beam area. The measured air kerma could be used for patient dose estimation. The air kerma and radiation quality dependence of the response of pixel values within a large exposure range for two direct digital detector types was experimentally investigated for this purpose. Using these calibration results, air kerma was measured from clinical images and compared with tube output calculation. The differences between the two methods were typically below 2% and measurements based on pixel values can therefore be recommended.

The energy dependence of the response of a patient dose calibrator.

Kerma-area product (KAP) meters used for patient exposure monitoring in diagnostic x-ray imaging can be calibrated in situ with a reference KAP meter. The drawback of this tandem calibration method is the large energy dependence of the response of the reference KAP meter when typical KAP ionization chambers are used for this purpose. The energy dependence of a novel, large-area KAP meter (patient dose calibrator, PDC, Radcal) was therefore experimentally investigated. Its response was examined by measuring the calibration coefficients for standard calibration radiation qualities and several radiation qualities in the range generally used in diagnostic x-ray imaging. The PDC type of KAP meter has a smaller energy dependence than conventional KAP meters, and the half-value layer can be used as a radiation quality specifier for PDC-type chambers with an uncertainty of less than 2%. The accuracy of the tandem calibration method can be improved by using this type of KAP meter as a reference meter.

Effects of radiation quality on the calibration of kerma-area product meters in x-ray beams.

The calibration coefficients of kerma-area product meters significantly depend on the energy spectrum of the x-ray beam. This effect was examined by measuring the calibration coefficients for several radiation qualities in the range generally used in diagnostic x-ray imaging. The intention was to determine the calibration coefficients for other radiation qualities by interpolation between the measured values, relative to one or more suitable parameters. The x-ray tube voltage, total filtration and half-value thickness were examined as possible specifiers of the energy distribution. No single parameter provided an interpolation of calibration coefficients with the accuracy recommended by the ICRU and IAEA, except for a narrow range of radiation qualities. At least two of the parameters are needed to reliably specify the radiation quality for the interpolation of calibration coefficients.

A tandem calibration method for kerma-area product meters.

For measurements of the kerma-area product (KAP) in diagnostic x-ray imaging, a method for calibrating field KAP meters with a reference KAP meter is presented. In this tandem calibration method, the field KAP chamber is positioned similarly as in measurements with patients. The reference KAP chamber is placed at a specified distance and used in the x-ray beam simultaneously with the field KAP chamber. The tandem method provides a feasible and practical way for calibrating field KAP meters of any type in their clinical position. Accurate measurements of the irradiation geometry are not required, but comprehensive calibration for the reference KAP meter is needed.