Practical guidance on the assessment of radiation risks for diagnostic radiological examinations.

Patient doses cannot be limited; instead, radiological examinations should be justified and optimised to ensure the necessary diagnostic or therapeutic effect with the lowest patient dose achievable. Assessment of the radiation risks from patient exposure is important part of the justification process. Hence, medical staff within the framework of their professional activities should possess necessary information on the data on radiation risk from different types of radiological procedures. An approach has been developed that allows considering age and gender dependences of the risk coefficients of radiogenic cancer and the age and gender distribution of patients for various radiological examinations to assess the individual radiation risk for patient and collective risk for population from medical exposure. The approach is based on a new expanded use of the effective dose concept proposed in ICRP Publication 147 and demonstrated using the medical exposure in the Russian Federation as the example. For 30 radiological examinations that compose about 80% of the collective dose from medical exposure of the public in the Russian Federation radiation risk was assessed based on calculated age and gender specific risk coefficients per unit effective dose. For the rest of the examinations a simplified approach was used to assess the risk, which was based on using an age and gender specific risk coefficient determined for one of 4 anatomical regions (head, neck, chest and abdomen) or for uniform irradiation of the whole body. The proposed approach allows significantly improving the assessment of the radiation risk while continuing to use the effective dose as a dosimetric quantity within the framework of the state program in the Russian Federation. As a result the collective risk from medical examinations in the Russian Federation in 2022 was lower by the factor of 3 compared to the previous assessment based on the effective dose with the nominal risk coefficient.

Evaluation of the Accuracy of Standardized Uptake Values of 18F-fluorodeoxyglucose in Lung Lesions Based on Phantom Studies.

The aim of the study was to estimate the accuracy of standardized uptake values of 18F-fluorodeoxyglucose (18F-FDG) in lung lesions during positron emission tomography combined with computed tomography (PET/CT) imaging, based on phantom studies performed for different PET/CT scanners. MATERIALS AND METHODS: The analysis of the PET/CT with 18F-FDG data was performed for 86 patients newly diagnosed with the lung lesions: malignant tumors (n=37), benign tumors and inflammatory diseases (n=49). The criteria for inclusion in the study were developed considering the recommendations of the Fleischner Society (2017). The characteristics of the lesions on CT met the following requirements: a round shape or close to it; total size of 8 to 30 mm; solid or subsolid structure (with the exception of lesion with ground-glass opacity); a solid part size of ≥8 mm. All the patients had no signs of pleurisy, lymphadenopathy, or cancer history. PET/CT imaging with 18F-FDG was performed with three scanners: Discovery 690 (General Electric, USA), Biograph mCT 128 (Siemens, Germany), and Biograph mCT 40 (Siemens); the preparation of patients prior to the scan was standardized. To determine the reference accumulation of a radiopharmaceutical in the pathological lesion, four scans of a specialized NEMA IEC PET Body Phantom Set (USA) were performed for each scanner. For each unit, the recovery coefficients (RCs) of radioactivity, maximum and recovered (corrected) standardized uptake values (SUVs) were determined. Statistical relationship between the size of lesions, SUVmax and SUVcorrect was evaluated. Data processing was performed using MedCalc v. 19.2.0 software. RESULTS: During the phantom study, the underestimation of the radioactivity was determined in the spheres with the diameters of 10 and 13 mm, overestimation was observed in the sphere with the diameter of 28 mm. Both underestimation and overestimation of radioactivity were determined for the spheres with a diameter of 17 and 22 mm.SUVmax differed from the reference values for 85 patients (98.8%). The underestimation of these values was found for 63 patients (73.2%) due to the partial volume effect. The greatest underestimation was observed for the patients with 8 mm diameter lesions. Depending on the scanner, the underestimation of the SUVmax in these patients reached up to 54-73%. For 9 patients (25%) with malignant tumors of 9-12 mm, the utility of RC made it possible to avoid false negative results. For the lesions with a diameter of 30 mm, an overestimation of SUVmax up to 22% was determined due to the negative influence of the reconstruction algorithms. CONCLUSION: The use of RC eliminates the influence of the partial volume effect and reconstruction methods on the accuracy of estimating the SUVmax in lung lesions, which ensures reproducibility, increase in the information content of the method, as well as the comparability of the results of PET/CT with 18F-FDG obtained on the different models of PET/CT units with different technological characteristics.

Optimisation of environmental remediation: how to select and use the reference levels.

A number of past industrial activities and accidents have resulted in the radioactive contamination of large areas at many sites around the world, giving rise to a need for remediation. According to the International Commission on Radiological Protection (ICRP) and International Atomic Energy Agency (IAEA), such situations should be managed as existing exposure situations (ExESs). Control of exposure to the public in ExESs is based on the application of appropriate reference levels (RLs) for residual doses. The implementation of this potentially fruitful concept for the optimisation of remediation in various regions is hampered by a lack of practical experience and relevant guidance. This paper suggests a generic methodology for the selection of numeric values of relevant RLs both in terms of residual annual effective dose and derived RLs (DRLs) based on an appropriate dose assessment. The value for an RL should be selected in the range of the annual residual effective dose of 1-20 mSv, depending on the prevailing circumstances for the exposure under consideration. Within this range, RL values should be chosen by the following assessment steps: (a) assessment of the projected dose, i.e. the dose to a representative person without remedial actions by means of a realistic model as opposed to a conservative model; (b) modelling of the residual dose to a representative person following application of feasible remedial actions; and (c) selection of an RL value between the projected and residual doses, taking account of the prevailing social and economic conditions. This paper also contains some recommendations for practical implementation of the selected RLs for the optimisation of public protection. The suggested methodology used for the selection of RLs (in terms of dose) and the calculation of DRLs (in terms of activity concentration in food, ambient dose rate, etc) has been illustrated by a retrospective analysis of post-Chernobyl monitoring and modelling data from the Bryansk region, Russia, 2001. From this example, it follows that analysis of real data leads to the selection of an RL from a relatively narrow annual dose range (in this case, about 2-3 mSv), from which relevant DRLs can be calculated and directly used for optimisation of the remediation programme.

Patient doses from medical examinations in Russia: 2009-2015.

The aim of this study was to evaluate adult patient doses in Russia in the context of patient protection. Effective doses from x-ray and nuclear medicine examinations were assessed using two approaches. The first was based on data collection performed by the authors in hospitals in St. Petersburg and other 17 Russian regions. The second approach was to assess mean doses through the collective dose estimated annually within the federal data bank ESKID. In 2015, 203 million examinations were conducted in Russia, i.e. 1.4 examinations per capita. The number of examinations has increased by 35% over the last 10 years. Patient doses from x-ray examinations are strongly dependent on the imaging modality. Mean dose increases by an order of magnitude with each x-ray modality from dental examinations (0.01-0.1 mSv) to radiography (0.1-1 mSv), fluoroscopy and CT (1-10 mSv) and to interventional examinations (more than 10 mSv). Mean doses for x-ray examinations are comparable with that of foreign countries. Scintigraphy examinations with 99mTc are associated with mean doses of 1-5 mSv. Mean doses from PET/CT whole body examinations are 15-25 mSv with similar contributions from CT and radiopharmaceuticals. In nuclear medicine, patient doses are lower compared to other countries. According to ESKID data the collective dose from medical exposure in Russia has decreased from 140 000 man-Sv in 2000 to 77 000 man-Sv in 2015. Medical exposure contributes about 13% into a total collective dose. The maximum contribution was from CT examinations, i.e. 45% in 2015. A range of mean doses between different hospitals was up to two orders of magnitude for radiography and one order of magnitude for CT. In interventional studies, the scatter of individual doses was significant. Significant variations in doses between hospitals and some regions indicate the potential for optimization with the focus on interventional examinations, CT and nuclear medicine examinations combined with CT.

PROPOSALS FOR THE ESTABLISHMENT OF NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR RADIOGRAPHY FOR ADULT PATIENTS BASED ON REGIONAL DOSE SURVEYS IN RUSSIAN FEDERATION.

In 2009-2014, dose surveys aimed to collect adult patient data and parameters of most common radiographic examinations were performed in six Russian regions. Typical patient doses were estimated for the selected examinations both in entrance surface dose and in effective dose. 75%-percentiles of typical patient effective dose distributions were proposed as preliminary regional diagnostic reference levels (DRLs) for radiography. Differences between the 75%-percentiles of regional typical patient dose distributions did not exceed 30-50% for the examinations with standardized clinical protocols (skull, chest and thoracic spine) and a factor of 1.5 for other examinations. Two different approaches for establishing national DRLs were evaluated: as a 75%-percentile of a pooled regional sample of patient typical doses (pooled method) and as a median of 75%-percentiles of regional typical patient dose distributions (median method). Differences between pooled and median methods for effective dose did not exceed 20%. It was proposed to establish Russian national DRLs in effective dose using a pooled method. In addition, the local authorities were granted an opportunity to establish regional DRLs if the local radiological practice and typical patient dose distributions are significantly different.

INVESTIGATION OF PARTIAL VOLUME EFFECT IN DIFFERENT PET/CT SYSTEMS: A COMPARISON OF RESULTS USING THE MADEIRA PHANTOM AND THE NEMA NU-2 2001 PHANTOM.

Positron emission tomography combined with computed tomography (PET/CT) is a quantitative technique used for diagnosing various diseases and for monitoring treatment response for different types of tumours. However, the accuracy of the data is limited by the spatial resolution of the system. In addition, the so-called partial volume effect (PVE) causes a blurring of image structures, which in turn may cause an underestimation of activity of a structure with high-activity content. In this study, a new phantom, MADEIRA (Minimising Activity and Dose with Enhanced Image quality by Radiopharmaceutical Administrations) for activity quantification in PET and single photon emission computed tomography (SPECT) was used to investigate the influence on the PVE by lesion size and tumour-to-background activity concentration ratio (TBR) in four different PET/CT systems. These measurements were compared with data from measurements with the NEMA NU-2 2001 phantom. The results with the MADEIRA phantom showed that the activity concentration (AC) values were closest to the true values at low ratios of TBR (<10) and reduced to 50 % of the actual AC values at high TBR (30-35). For all scanners, recovery of true values became closer to 1 with an increasing diameter of the lesion. The MADEIRA phantom showed good agreement with the results obtained from measurements with the NEMA NU-2 2001 phantom but allows for a wider range of possibilities in measuring image quality parameters.

PATIENT DOSES IN COMPUTED TOMOGRAPHY EXAMINATIONS IN TWO REGIONS OF THE RUSSIAN FEDERATION.

Computed tomography (CT) is often a justified diagnostic tool, but is also associated with high exposure of the patients. Due to the rapid increase in the number of CT units and thus the availability of CT examinations in Russia, there is a growing need for optimisation within this field. In order to develop proper optimisation procedures for CT, the two regions St. Petersburg and Belgorod of Russia were chosen, representing an urban and a rural region, respectively. In 2014, a survey was conducted of the parameters applied in CT examinations in these regions, and the results show that the highest effective doses were observed for investigations of abdomen, reaching up to 137 mSv, and pelvic CT examinations, reaching up to 58 mSv, both with contrast agents. The dose distributions were approximately log-normal, and for the majority of the examinations, the 75th percentiles of the CT dose distributions in the Belgorod region were higher than observed in St. Petersburg. The aim of the current project is primarily to define and implement diagnostic reference levels as a part of the process of optimisation of CT examinations in Russia.

Russian practical guidance on radiological support for justification of X-ray and nuclear medicine examinations.

An important part of the justification process is assessment of the radiation risks caused by exposure of a patient during examination. The authors developed official national methodology both for medical doctors and sanitary inspectors called 'assessment of radiation risks of patients undergoing diagnostic examinations with the use of ionizing radiation'. The document addresses patients of various age groups and a wide spectrum of modern X-ray and nuclear medicine examinations. International scale of risk categorisation was implemented by the use of effective dose with account for age dependence of radiation risk. The survey of effective doses in radiology, including CT, mammography, and intervention radiology, and nuclear medicine, including single-photon emission tomography and positron emission tomography, for patients of various age groups from several regions of Russia was used for the risk assessment. The output of the methodology is a series of tables for each diagnostic technology with lists of examinations for three age groups (children/adolescents, adults and seniors) corresponding to various radiation risk categories.

Nuclear medicine examinations of children in Russia.

The number and specification of radionuclide examinations, administrated activity and effective doses were collected during 2011-13 for 4944 paediatric patients from 10 nuclear medicine (NM) departments of some Russian regions. The kidney examinations account for about 70 % of paediatric NM examinations in general hospitals. Diagnostics of all other organs contribute from 2 to 8 % each in the total number of paediatric examinations. Administrated activities of radiopharmaceuticals are approximately proportional to the child's age, and variations between different hospitals usually are within the factor of 3-4 and for some types of examination up to 10. The range of the effective dose due to paediatric NM examinations is roughly estimated as 2-6 mSv per examination, approximately the same as in adults. Some examinations (heart, thyroid, whole body) result in doses of younger children that are 2-3 times higher than the doses of adults. Effective doses in paediatric positron emission tomography (PET) diagnostics are in the range of 4-10 mSv per examination and are higher compared with the dose of adult patients. The application of combined radiodiagnostic technologies (single photon emission computer tomography with roentghen computer tomography [SPECT/CT] or PET with roetghen computer tomography [PET/CT]) increases the effective dose of patients by the factor of 1.5-2 for the skeleton or whole body examinations.