Low-Dose Chest CT Protocols for Imaging COVID-19 Pneumonia: Technique Parameters and Radiation Dose.

Chest computed tomography (CT) plays a vital role in the early diagnosis, treatment, and follow-up of COVID-19 pneumonia during the pandemic. However, this raises concerns about excessive exposure to ionizing radiation. This study aimed to survey radiation doses in low-dose chest CT (LDCT) and ultra-low-dose chest CT (ULD) protocols used for imaging COVID-19 pneumonia relative to standard CT (STD) protocols so that the best possible practice and dose reduction techniques could be recommended. A total of 564 articles were identified by searching major scientific databases, including ISI Web of Science, Scopus, and PubMed. After evaluating the content and applying the inclusion criteria to technical factors and radiation dose metrics relevant to the LDCT protocols used for imaging COVID-19 patients, data from ten articles were extracted and analyzed. Technique factors that affect the application of LDCT and ULD are discussed, including tube current (mA), peak tube voltage (kVp), pitch factor, and iterative reconstruction (IR) algorithms. The CTDIvol values for the STD, LDCT, and ULD chest CT protocols ranged from 2.79-13.2 mGy, 0.90-4.40 mGy, and 0.20-0.28 mGy, respectively. The effective dose (ED) values for STD, LDCT, and ULD chest CT protocols ranged from 1.66-6.60 mSv, 0.50-0.80 mGy, and 0.39-0.64 mSv, respectively. Compared with the standard (STD), LDCT reduced the dose reduction by a factor of 2-4, whereas ULD reduced the dose reduction by a factor of 8-13. These dose reductions were achieved by applying scan parameters and techniques such as iterative reconstructions, ultra-long pitches, and fast spectral shaping with a tin filter. Using LDCT, the cumulative radiation dose of serial CT examinations during the acute period of COVID-19 may have been inferior or equivalent to that of conventional CT.

Typical effective dose values from diagnostic and interventional radiology.

Effective dose (E) in medical procedures is of practical value for comparing doses from different types of procedures which is not possible with the different measurable dose quantities. In this survey we estimated and compared the values of E in 12 medical imaging procedures. The mean E for conventional X-ray in mSv were ranged between 0.01 for skull lateral to 0.5 for abdominal while the mean E for cardiac interventional radiology in mSv was up to 16 for percutaneous transluminal coronary angioplasty (PTCA). For dental radiology the mean E in µSv was 1.2 for intraoral and 10 for panoramic. In mammography the mean E was 0.5 mSv. Compared with the literature, chest postero-anterior (PA), lumbar spine AP, PTCA and mammography procedures had shown larger E values. The obtained results can help in justification of techniques.

NATIONAL DIAGNOSTIC REFERENCE LEVELS AND ACHIEVABLE DOSES FOR STANDARD CT EXAMINATIONS IN SUDAN.

Radiation doses were determined to propose national diagnostic reference levels (NDRLs) and achievable doses (ADs) for computed tomography (CT) examinations in Sudan. Doses were estimated from retrospectively collected scan parameters for 1336 CT examinations of adult patients from 14 Sudanese hospitals using CT Expo 2.5 software. ADs and NDRLs were set at the 50th and 75th percentile of the hospital median dose distribution, respectively. The proposed CTDIvol (mGy) ADs ranged from: 10 (chest) to 64 (head), and that of the dose-length product (DLP; mGy.cm) ranged from 366 (chest) to 1225 (head). The proposed CTDIvol (mGy) NDRLs ranged from 15 kidney-ureter-bladder (KUB) to 79 (head), whereas that of the DLP (mGy.cm) ranged from 690 (chest) to 1490 (head). Current doses fell within the upper range of the doses presented in the literature emphasizing the need for implementation of the current ADs and NDRLs for CT to enhance patient protection and dose optimization in Sudan.

PROPOSED NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR STANDARD RADIOGRAPHIC X-RAY PROCEDURES IN SUDAN.

This study aimed to calculate patient radiation doses for adults during the seven most commonly performed conventional X-ray procedures, and to propose national diagnostic reference levels (DRLs). A representative sample of patients from 29 hospitals was included. The entrance surface air kerma (ESAK) was calculated by measuring X-ray tube output and the corresponding technical and exposure factors for each patient. Third-quartile values of the mean ESAK distributions were proposed as DRL values. The DRLs in mGy were as follows: 0.6 for chest postero-anterior (PA), 3.5 for skull AP, 1.7 for skull lateral (LAT), 2.7 for abdominal, 2.6 for pelvic AP, 3.7 for lumbar spine AP and 8 for lumbar spine LAT. Compared with literature, the maximum percentages increase were in chest PA (329%) and skull AP (187%). Since the suggested DRL for chest PA was higher than literature values, dose optimization and a review of its value is recommended.

PEDIATRIC RADIATION DOSE DURING CARDIAC CATHETERIZATION PROCEDURES IN SUDAN.

Children are more radio sensitive than adult. This study aims to assess radiation doses and the associated hazards to pediatric during cardiac catheterization procedures. Radiation dose for 112 patients was estimated in the biggest cardiac center in Sudan. The median KAP in Gy cm2, CK in mGy, number of frames and fluoroscopy time in minutes were (4.6, 29.0, 340.4, 13.5) and (6.0, 35.0, 318, 9.8) for the diagnostic and therapeutic cardiac procedures, respectively. The median (KAP in Gy cm2, effective dose in mSv) for different age groups in the intervals of less than 1 year, 1-<5 years, 5-<10 years and 10-15 years old were (2.2, 4.4), (2.5, 5.0), (4.2, 5.1) and (8.5, 4.1) respectively. Including all the procedures using the multiplicative model of ICRP 60, the mean attributable lifetime risk for stochastic effect was 0.08 and 0.05% for girls and boys, respectively. Training is needed to raise staff awareness about radiation protection.

Examination frequency and population dose from medical X-ray examinations in Sudan in 2010.

This study was performed to estimate examination frequency and collective and per caput effective doses arising from medical X-ray procedures in Sudan, 2010. Information was collected from 30 hospitals performing radiography, computed tomography (CT), fluoroscopy and interventional radiology (IR) procedures. The estimated annual number of examinations was 33 million radiographic X-ray procedures (99 %), 0.34 million CT exams per year (14 % paediatrics CT), 0.02 million fluoroscopy and IR procedures. The estimated annual number of examinations was 326 per 1000 people. The estimated annual collective and per caput effective doses from medical X-ray procedures mount 7197 man Sv and 0.18 mSv, respectively. The study offered the first projection of frequency and population dose from medical X-ray examinations in Sudan and provides estimates of the impact of the medical X-ray procedures at the national level.

IAEA survey of paediatric computed tomography practice in 40 countries in Asia, Europe, Latin America and Africa: procedures and protocols.

OBJECTIVE: To survey procedures and protocols in paediatric computed tomography (CT) in 40 less resourced countries. METHODS: Under a project of the International Atomic Energy Agency, 146 CT facilities in 40 countries of Africa, Asia, Europe and Latin America responded to an electronic survey of CT technology, exposure parameters, CT protocols and doses. RESULTS: Modern MDCT systems are available in 77 % of the facilities surveyed with dedicated paediatric CT protocols available in 94 %. However, protocols for some age groups were unavailable in around 50 % of the facilities surveyed. Indication-based protocols were used in 57 % of facilities. Estimates of radiation dose using CTDI or DLP from standard CT protocols demonstrated wide variation up to a factor of 100. CTDI(vol) values for the head and chest were between two and five times those for an adult at some sites. Sedation and use of shielding were frequently reported; immobilisation was not. Records of exposure factors were kept at 49 % of sites. CONCLUSION: There is significant potential for improvement in CT practice and protocol use for children in less resourced countries. Dose estimates for young children varied widely. This survey provides critical baseline data for ongoing quality improvement efforts by the IAEA.

Patient doses in interventional cardiology procedures in Sudan.

Radiation doses delivered to 461 patients were measured during the period of 12 months in a hospital in Khartoum, Sudan. Kerma Area Product, Cumulative Kerma and fluoroscopy time were registered during four selected procedures, namely coronary angiography (CA), percutaneous transluminal coronary angioplasty (PTCA), percutaneous transvenous mitral commissurotomy (PTMC) and pacemaker. For CA, PTCA, PTMC and pacemaker the mean and median kerma area product values in gray centimeter square were found to be (20, 17.9), (56.5, 50.3), (21.6, 19.6) and (15.3, 9.6), respectively. The obtained results for mean and median cumulative kerma in milli gray were (143.7, 120.5), (418.4, 371.4), (119.8, 102) and (88.7, 59.8) as measured for CA, PTCA, PTMC and pacemaker, respectively. The mean and median total fluoroscopy time in minutes were (5.2, 3.39), (17.6, 14.8), (18, 15) and (10.2, 7.16) as registered for CA, PTCA, PTMA and pacemaker, respectively. Maximum skin dose was estimated for 13 patients during PTCA and CA procedures. Dose exceeded 2 Gy in PTCA for one patient. In comparison with the guidelines for coronary examinations suggested by SENTINEL Consortium, a higher fluoroscopy time for PTCA procedure is reported in this study. It is realised that proper selection of irradiation area, technique modes, fluoroscopy time and conducting special training on radiation protection to the operators are the main factors for potential optimisation.

Equipment performance and radiation protection status in X-ray fluoroscopy units in Sudan.

The number of fluoroscopy and fluoroscopically guided procedures has been substantially growing in developing countries at the same time advanced and sophisticated equipment are used in some hospitals. However, radiation protection requirements are not necessarily well adopted. In this study nine fluoroscopy X-ray units in Sudan were examined for compliance with international standards. The tests included: beam quality, entrance surface air kerma, image quality and radiation field measurements. Staff radiation protection tools such as lead aprons and eye glasses were also visually examined to find out whether international recommendations were fulfilled and to determine the level of staff awareness. The measured peak tube voltage deviation exceeded the recommended tolerance level in 30 % of the measurements. The results of patient doses measurements exceeded the recommended reference dose levels in 43 % of the measurements; however image quality and radiation field generally fulfilled the requirements for most units. The study revealed that a considerable number of fluoroscopy units were not performing according to the international standards and highlights the need of optimisation of radiation protection.

Survey of computed tomography technique and radiation dose in Sudanese hospitals.

The purpose of this study was to survey technique and radiation absorbed dose in CT examinations of adult in Sudan and to compare the results with the reference dose levels. Questionnaire forms were completed in nine hospitals and a sample of 445 CT examinations in patients. Information on patient, procedure, scanner, and technique for common CT examinations were collected. For each facility, the radiation absorbed dose was measured on CT dose phantom measuring 16 cm (head) and 32 cm (body) in diameter and was used to calculate the normalized CT air kerma index. Volume CT air kerma index (CVOL), CT air kerma-length product (PKL,CT) values were calculated using the measured normalized CT air kerma index and questionnaire information. The effective dose, E estimates was determined by using PKL,CT measurements and appropriate normalized coefficients. Assuming the sample to offer a fair representative picture of CT practice patterns in Sudan, the mean CVOL and PKL,CT values were comparable or below the reference doses: 65 mGy and 758 mGy cm, respectively at head CT; 11.5 mGy and 327 mGy cm, respectively at chest CT; 11.6 mGy and 437 mGy cm, respectively at abdominal CT; and 11.0 mGy and 264 mGy cm, respectively at pelvis CT. Estimated effective doses were 1.6, 4.6, 6.6 and 4.0 mSv, respectively. The study offered a first national dose survey and provided a mean for quality control and optimization of CT practice within the country.

Radiation exposure to patients during interventional procedures in 20 countries: initial IAEA project results.

OBJECTIVE: The purpose of our study was to investigate the level of radiation protection of patients and staff during interventional procedures in 20 countries of Africa, Asia, and Europe. SUBJECTS AND METHODS: In a multinational prospective study, information on radiation protection tools, peak skin dose (PSD), and kerma-area product (KAP) was provided by 55 hospitals in 20 mainly developing countries (nine mostly in Eastern Europe, five in Africa, and six in Asia). RESULTS: Nearly 40% of the interventional rooms had an annual workload of more than 2,000 patients. It is remarkable that the workload of pediatric interventional procedures can reach the levels of adult procedures even in developing countries. About 30% of participating countries have shown a 100% increase in workload in 3 years. Lead aprons are used in all participating rooms. Even though KAP was available in almost half of the facilities, none had experience in its use. One hundred of 505 patients monitored for PSD (20%) were above the 2-Gy threshold for deterministic effects. CONCLUSION: Interventional procedures are increasing in developing countries, not only for adults but also for pediatric patients. The situation with respect to staff protection is considered generally acceptable, but this is not the case for patient protection. Many patients exceeded the dose threshold for erythema. A substantial number (62%) of percutaneous transluminal coronary angioplasty procedures performed in developing countries in this study are above the currently known dose reference level and thus could be optimized. Therefore, this study has significance in introducing the concept of patient dose estimation and dose management.

Patient doses in radiographic examinations in 12 countries in Asia, Africa, and Eastern Europe: initial results from IAEA projects.

OBJECTIVE: The purpose of this study was to survey image quality and the entrance surface air kerma for patients in radiographic examinations and to perform comparisons with diagnostic reference levels. SUBJECTS AND METHODS: In this multinational prospective study, image quality and patient radiation doses were surveyed in 12 countries in Africa, Asia, and Eastern Europe, covering 45 hospitals. The rate of unsatisfactory images and image quality grade were noted, and causes for poor image quality were investigated. The entrance surface doses for adult patients were determined in terms of the entrance surface air kerma on the basis of X-ray tube output measurements and X-ray exposure parameters. Comparison of dose levels with diagnostic reference levels was performed. RESULTS: The fraction of images rated as poor was as high as 53%. The image quality improved up to 16 percentage points in Africa, 13 in Asia, and 22 in Eastern Europe after implementation of a quality control (QC) program. Patient doses varied by a factor of up to 88, although the majority of doses were below diagnostic reference levels. The mean entrance surface air kerma values in mGy were 0.33 (chest, posteroanterior), 4.07 (lumbar spine, anteroposterior), 8.53 (lumbar spine, lateral), 3.64 (abdomen, anteroposterior), 3.68 (pelvis, anteroposterior), and 2.41 (skull, anteroposterior). Patient doses were found to be similar to doses in developed countries and patient dose reductions ranging from 1.4% to 85% were achieved. CONCLUSION: Poor image quality constitutes a major source of unnecessary radiation to patients in developing countries. Comparison with other surveys indicates that patient dose levels in these countries are not higher than those in developed countries.